Papers & publications

2017

Auer, S., Zeiringer, B., Fuhrer, S., Tonolla, D., Schmutz, S. (2017). Effects of river bank heterogeneity and time of day on drift and stranding of juvenile European grayling (Thymallus thymallus L.) caused by hydropeaking. Science of the Total Environment 575, 1515-1521, http://dx.doi.org/10.1016/j.scitotenv.2016.10.029

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Effects of river bank heterogeneity and time of day on drift and stranding of juvenile European grayling (Thymallus thymallus L.) caused by hydropeaking

High-head storage hydropower is deemed to be the ideal renewable energy source in Alpine regions to meet the increasing demand for daily peak electrical energy. However, this mode of operation - called hydropeaking - can imply severe hydrological and hydromorphological consequences for river ecosystems, affecting fish populations by e.g. drift and stranding of young life stages. Several fish-stranding experiments using physical models have been performed in the past, but until now very little is known about influences of time of day or gravel bank heterogeneity.


Baattrup-Pedersen, A., Göthe, E., Riis, T., Andersen, D. K., Larsen, S. E. (2017). A new paradigm for bio-monitoring - An example building on the Danish Stream Plant Index. Methods in Ecology and Evolution 8, 297-307, http://dx.doi.org/10.1111/2041-210X.12676

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A new paradigm for biomonitoring: an example building on the Danish Stream Plant Index

1. Despite intensive efforts for more than a decade to develop Water Framework-compliant assessment systems, shortcomings continue to appear. In particular, the lack of reference conditions has hindered the development of assessment systems capturing the heart of the Water Framework Directive (WFD) – that ecological status should be set as the deviation from the natural, undisturbed condition. Recently, the Danish Stream Plant Index (DSPI) was developed. This system contrasts existing systems in that it builds on an expert interpretation of the normative definitions of ecological status classes in the WFD without taking pressure–impact relationships into account.

2. Here, we substantiate the approach taken in the development of DSPI and examine whether the DSPI class decreases with increasing level of anthropogenic stress and, additionally, whether the deviation from the natural undisturbed condition increases with decreasing DSPI class sensu WFD using trait composition of plant assemblages from Danish streams around year 1900 as a reference. We furthermore examine the trait composition of the vegetation in sites classified into different DSPI status classes to explore whether predictable patterns exist that can be used to identify the ultimate cause(s) of failure to meet ecological goals and help guide the selection of appropriate mitigation measures.

3. We observed that DSPI declined with several parameters indicative of environmental stress in Danish streams and, furthermore, that the deviation from the natural undisturbed condition regarding the trait composition of plant communities declined with increasing DSPI, implying that the trait composition of plant communities in the high DSPI status class was most similar to those occurring in Danish streams around year 1900. We also found that trait characteristics capable of disentangling important stressors in Danish streams varied consistently among sites classified into different DSPI classes.

4. Based on our findings, we call for new thinking. We suggest that more effort should be directed at describing reference conditions and interpreting the normative definitions of good, moderate, poor and bad instead of focusing solely on developing assessment systems using pressure–impact frameworks. We find this particularly important with respect to streams as these are seldom impacted by only a single stressor.


Beklioğlu, M., Bucak, T., Coppens, J., Bezirci, G., Tavşanoğlu, Ü. N., Çakıroğlu, A. İ., Levi, E. E., Erdoğan, Ş., Filiz, N., Özkan, K., Özen, A. (2017). Restoration of eutrophic lakes with fluctuating water levels: A 20 year monitoring study of 2 inter-connected lakes. Water 9, 127, http://dx.doi.org/10.3390/w9020127

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Restoration of eutrophic lakes with fluctuating water levels: A 20 year monitoring study of 2 inter-connected lakes

Eutrophication continues to be the most important problem preventing a favorable environmental state and detrimentally impacting the ecosystem services of lakes. The current study describes the results of analyses of 20 year monitoring data from two interconnected Anatolian lakes, Lakes Mogan and Eymir, receiving sewage effluents and undergoing restoration. The first step of restoration in both lakes was sewage effluent diversion. Additionally, in hypertrophic Lake Eymir, biomanipulation was conducted, involving removal of benthi-planktivorous fish and prohibition of pike fishing. The monitoring period included high (H) and low (L) water levels (WL) enabling elucidation of the effects of hydrological changes on lake restoration. In shallower Lake Mogan, macrophyte abundance increased after the sewage effluent diversion in periods with low water levels even at turbid water. In comparatively deeper Lake Eymir, the first biomanipulation led to a clear water state with abundant macrophyte coverage. However, shortly after biomanipulation, the water clarity declined, coinciding with low water level (LWL) periods during which nutrient concentrations increased. A second biomanipulation was conducted, mostly during high water level (HWL) period, resulting in a major decrease in nutrient concentrations and clearer water, but without an expansion of macrophytes. We conclude that repetitive fish removal may induce recovery but its success may be confounded by high availability of nutrients and adverse hydrological conditions.


Bucak, T., Trolle, D., Andersen, H. E., Thodsen, H., Erdogan, S., Levi, E. E., Filiz, N., Jeppesen, E., Beklioglu, M. (2017). Future water availability in the largest freshwater Mediterranean lake is at great risk as evidenced from simulations with the SWAT model. Science of the Total Environment 581-582, 413-425, http://dx.doi.org/10.1016/j.scitotenv.2016.12.149

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Future water availability in the largest freshwater Mediterranean lake is at great risk as evidenced from simulations with the SWAT model

Inter- and intra-annual water level fluctuations and changes in water flow regime are intrinsic characteristics of Mediterranean lakes. Additionally, considering climate change projections for the water-limited Mediterranean region, increased air temperatures and decreased precipitation are anticipated, leading to dramatic declines in lake water levels as well as severe water scarcity problems. The study site, Lake Beyşehir, the largest freshwater lake in the Mediterranean basin, is – like other Mediterranean lakes – threatened by climatic changes and over-abstraction of water for irrigated crop farming. Therefore, implementation of strict water level management policies is required. In this study, an integrated modeling approach was used to predict the future water levels of Lake Beyşehir in response to potential future changes in climate and land use. Water level estimation was performed by linking the catchment model Soil and Water Assessment Tool (SWAT) with a Support Vector Regression model (ε-SVR). The projected increase in temperature and decrease in precipitation based on the climate change models led to an enhanced potential evapotranspiration and reduced total runoff. On the other hand, the effects of various land use scenarios within the catchment appeared to be comparatively insignificant. According to the ε-SVR model results, changes in hydrological processes caused a water level reduction for all scenarios. Moreover, the MPI-ESM-MR General Circulation Model outputs produced the most dramatic results by predicting that Lake Beyşehir may dry out by the 2040s with the current outflow regime. The results indicate that shallow Mediterranean lakes may face a severe risk of drying out and losing their ecosystem values in the near future if the current intensity of water abstraction is not reduced. In addition, the results also demonstrate that outflow management and sustainable use of water sources are vital to sustain lake ecosystems in water-limited regions.


Cao Y., Olsen, S., Gutierrez, M. F., Brucet, S., Davidson, T. A., Li, W., Lauridsen, T. L., Søndergaard, M., Jeppesen, E. (2017). Temperature effects on periphyton, epiphyton and epipelon under a nitrogen pulse in low-nutrient experimental freshwater lakes. Hydrobiologia 787(1), online, http://dx.doi.org/10.1007/s10750-017-3140-4

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Temperature effects on periphyton, epiphyton and epipelon under a nitrogen pulse in low-nutrient experimental freshwater lakes

The ongoing global climate change involves not only increased temperatures but may also produce more frequent extreme events, such as severe rainfall that could trigger a pulse of nutrients to lakes. In shallow lakes, this may affect primary producers through a number of direct and indirect mechanisms. We conducted a six-month mesocosm experiment to elucidate how periphyton (on inert substrata), epiphyton and epipelon biomass responded to a nitrogen (N) pulse, an approximately tenfold enrichment of the NO3-pool, under three contrasting warming scenarios: ambient temperature and ca. +3°C and ca. +4.5°C elevated temperatures (hereafter T1, T2 and T3). After the N pulse, we found a higher periphyton biomass at elevated than at ambient temperatures but no change in epiphyton biomass. Epipelon biomass was lower in T3 than in T1. Both periphyton and epiphyton biomasses correlated negatively with snail biomass, while epiphyton biomass correlated positively with light. Different responses to higher temperatures under short-term extreme nutrient loading conditions may be attributed to differences in the access to nutrient sources and light. Our data suggest that the biomass of periphyton in oligotrophic clear-water lakes will increase significantly under conditions exhibiting short-term extreme nutrient loading in a warmer climate.


Cremona, F., Vilbaste, S., Couture, R.M., Nõges, P., Nõges, T. (2017). Is the future of large shallow lakes blue-green? Comparing the response of a catchment-lake model chain to climate predictions. Climatic Change 141(2), 347-361, http://dx.doi.org/10.1007/s10584-016-1894-8

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Is the future of large shallow lakes blue-green? Comparing the response of a catchment-lake model chain to climate predictions

We constructed a model chain into which regional climate-related variables (air temperature, precipitation) and a lake’s main tributary hydrological indicators (river flow, dissolved inorganic carbon) were employed for predicting the evolution of planktonic blue-green algae (cyanobacteria) and zooplankton (rotifer) biomass in that lake for the mid-21st century. Simulations were based on the future climate predicted under both the Representative Concentration Pathways 4.5 and 8.5 scenarios which, combined with three realistic policy-making and basin land-use evolution lead to six scenarios for future water quality. Model outputs revealed that mean annual river flow is expected to decline between 3 to 20%, depending of the scenario. Concentration of river dissolved inorganic carbon is predicted to follow the opposite trend and might soar up to twice the 2005-2014 average concentration. Lake planktonic primary producers will display quantitative changes in the future decades whereas zooplankters will not. A 2 to 10% increase in mean cyanobacteria biomass is accompanied by a stagnation (-3 to +2%) of rotifer biomass. Changes in cyanobacteria and rotifer phenology are expected: a surge of cyanobacteria biomass in winter and a shortening of the rotifer biomass spring peak. The expected quantitative changes on the biota were magnified in those scenarios where forested area conversion to cropland and water abstraction were the greatest.


Ding, N., Yang, W., Zhou Y., Gonzalez-Bergonzoni, I., Zhang, J., Chen, K., Jeppesen, E. & Wang, B. (2017) Different response of species traits and functional diversity indices of stream macroinvertebrates to environmental and spatial factors in the Xishuangbanna watershed, upper Mekong River Basin, China, Science of the Total Environment 574, 288-299, http://dx.doi.org/10.1016/j.scitotenv.2016.09.053

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Different responses of functional traits and diversity of stream macroinvertebrates to environmental and spatial factors in the Xishuangbanna watershed of the upper Mekong River Basin, China

Functional traits and diversity indices have provided new insights into community responses to stressors. Most traits of aquatic organisms have frequently been tested for predictability and geographical stability in response to environmental variables, but such tests of functional diversity indices are rare. We sampled macroinvertebrates at 18 reference sites (RS) and 35 disturbed sites (DS) from headwater streams in the upper Mekong River Basin, Xishuangbanna (XSBN), China. We selected 29 qualitative categories of eight traits and then calculated five functional diversity indices, namely functional richness (FRic), functional evenness (FEve), functional dispersion (FDis), functional divergence (FDiv) and Rao's Quadratic Entropy (RaoQ), and two trait diversity indices, namely trait richness (TR) and trait diversity (TD). We used combination of RLQ and fourth-corner to examine the response of traits and functional diversity to the disturbance and environmental variables. We used variance partitioning to explore the relative role of environmental variables and spatial factors in constraining trait composition and functional diversity. We found that the relative frequency of ten trait categories, and the values of TD, TR, FRic and FDis in RS were significantly different (p<0.05) from DS. In addition, the seven traits (except for "habit") demonstrated a predictable response of trait patterns along the integrative environmental gradients. Environmental variables significantly contributed to most of the traits, functional diversity and trait diversity. However, spatial variables were mainly significant in shaping ecological traits, FRic and FEve. Our results confirm the dominant role of environmental variables in the determination of community trait composition and functional diversity, and substantiate the contribution of spatial vectors in explaining the variance of functional traits and diversity. We conclude that the traits "Refuge", "External protection", "Respiration" and "Body shape", and diversity indices FDis, TD, and TR are promising indicators of stream conditions at XSBN.


Gao J., Zhong, P., Ning, J., Liu, Z., Jeppesen, E. (2017). Herbivory of omnivorous fish shapes the food web structure of a Chinese tropical eutrophic lake: Evidence from stable isotope and fish gut content analyses. Water 9(1), 69, http://dx.doi.org/10.3390/w9010069

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Herbivory of omnivorous fish shapes the food web structure of a Chinese tropical eutrophic lake: Evidence from stable isotope and fish gut content analyses

Studies suggest that, unlike the situation in temperate lakes, high biomasses of omnivorous fish are maintained in subtropical and tropical lakes when they shift from a turbid phytoplankton-dominated state to a clear water macrophyte-dominated state, and the predation pressure on large-bodied zooplankton therefore remains high. Whether this reflects a higher degree of herbivory in warm lakes than in temperate lakes is debatable. We combined food web studies using stable isotopes with gut content analyses of the most dominant fish species to elucidate similarities and differences in food web structure between a clear water macrophyte-dominated basin (MDB) and a turbid phytoplankton-dominated basin (PDB) of Huizhou West Lake, a shallow tropical Chinese lake. The δ 13 C–δ 15 N biplot of fish and invertebrates revealed community-wide differences in isotope-based metrics of the food webs between MDB and PDB. The range of consumer δ 15 N (NR) was lower in MDB than in PDB, indicating shorter food web length in MDB. The mean nearest neighbor distance (MNND) and standard deviation around MNND (SDNND) were higher in MDB than in PDB, showing a markedly low fish trophic overlap and a more uneven packing of species in niches in MDB than in PDB. The range of fish δ 13 C (CR) of consumers was more extensive in MDB than in PDB, indicating a wider feeding range for fish in MDB. Mixing model results showed that macrophytes and associated periphyton constituted a large fraction of basal production sources for the fish in MDB, while particulate organic matter (POM) contributed a large fraction in PDB. In MDB, the diet of the dominant fish species, crucian carp (Carassius carassius), consisted mainly of vegetal matter (macrophytes and periphyton) and zooplankton, while detritus was the most important food item in PDB. Our results suggest that carbon from macrophytes with associated periphyton may constitute an important food resource for omnivorous fish, and this may strongly affect the feeding niche and the strength of the top-down trophic cascade between fish and zooplankton in the restored, macrophyte-dominated basin of the lake. This dual effect (consumption of macrophytes and zooplankton) may reduce the chances of maintaining the clear water state at the prevailing nutrient levels in the lake, and regular removal of large crucian carp may therefore be needed to maintain a healthy ecosystem state.


Gonzalez-Bergonzoni, I., Johansen, K. L., Mosbech, A., Landkildehus, F., Jeppesen, E., Davidson, T. A. (2017). Small birds, big effects: The little auk (Alle alle) transforms high Arctic ecosystems. Proceedings of the Royal Society B: Biological Sciences 284(1849), 20162572, http://dx.doi.org/10.1098/rspb.2016.2572

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Small birds, big effects: The little auk (Alle alle) transforms high Arctic ecosystems

In some arctic areas, marine-derived nutrients (MDN) resulting from fish migrations fuel freshwater and terrestrial ecosystems, increasing primary production and biodiversity. Less is known, however, about the role of seabird-MDN in shaping ecosystems. Here, we examine how the most abundant seabird in the North Atlantic, the little auk (Alle alle), alters freshwater and terrestrial ecosystems around the North Water Polynya (NOW) in Greenland. We compare stable isotope ratios (δ15N and δ13C) of freshwater and terrestrial biota, terrestrial vegetation indices and physical–chemical properties, productivity and community structure of fresh waters in catchments with and without little auk colonies. The presence of colonies profoundly alters freshwater and terrestrial ecosystems by providing nutrients and massively enhancing primary production. Based on elevated δ15N in MDN, we estimate that MDN fuels more than 85% of terrestrial and aquatic biomass in bird influenced systems. Furthermore, by using different proxies of bird impact (colony distance, algal δ15N) it is possible to identify a gradient in ecosystem response to increasing bird impact. Little auk impact acidifies the freshwater systems, reducing taxonomic richness of macroinvertebrates and truncating food webs. These results demonstrate that the little auk acts as an ecosystem engineer, transforming ecosystems across a vast region of Northwest Greenland.


Göthe, E., Baattrup-Pedersen, A., Wiberg-Larsen, P., Graeber, D., Kristensen, E. A., Friberg, N. (2017). Environmental versus spatial control of taxonomic and trait composition of stream biota in a European lowland region. Freshwater Biology 62(2), 397-413, http://dx.doi.org/10.1111/fwb.12875

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Environmental versus spatial control of taxonomic and trait composition of stream biota in a European lowland region

The spatial organisation of biotic communities derives from factors operating at a wide range of spatial and temporal scales. Despite strong scientific evidence of prevalent spatial control of community composition in freshwater ecosystems, local environmental factors are often considered as the main drivers of community change. Furthermore, taxonomic approaches are most frequently used, and few studies have compared the relative importance of local and regional control of trait versus the taxonomic composition in stream ecosystems. Using a spatially dense data set covering all stream sizes in a lowland European region of c. 42 000 km2 and three organism groups (macrophytes, macroinvertebrates and fishes), we compared the relative importance of spatial and environmental determinants of species and trait composition in the study streams, classified into headwaters (stream order 1–2) and downstream sites (stream order >2). We hypothesised that (i) there is a higher correspondence between environmental conditions and trait composition than with species composition, (ii) dispersal limitation (pure spatial structuring) is greater in headwaters than in downstream sites and (iii) dispersal limitation (pure spatial structuring) is weakest for macroinvertebrates, intermediate for macrophytes and strongest for fishes. The most consistent pattern across organisms and stream order groups was a higher correspondence between environmental variation and trait composition as well as a higher number of environmental variables significantly related to trait composition than with species composition (hypothesis 1). Spatial structuring peaked in headwater macrophyte communities and downstream fish communities (hypotheses 2 & 3) – a pattern that was amplified when separate analyses of traits describing species dispersal potential were undertaken. Our study highlights the potential of traits to capture multiple environmental changes in stream ecosystems and illustrates how organism-specific and highly context-dependent patterns in community organisation can emerge as a consequence of interactions between habitat connectivity (i.e. top versus lower parts of the stream network) and organism dispersal potential.


Grizzetti, B., Pistocchi, A., Liquete, C., Udias, A., Bouraoui, F., van de Bund, W. (2017). Human pressures and ecological status of European rivers. Scientific Reports 7(1), 205, http://dx.doi.org/10.1038/s41598-017-00324-3

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Human pressures and ecological status of European rivers

Humans have increased the discharge of pollution, altered water flow regime and modified the morphology of rivers. All these actions have resulted in multiple pressures on freshwater ecosystems, undermining their biodiversity and ecological functioning. The European Union has adopted an ambitious water policy to reduce pressures and achieve a good ecological status for all water bodies. However, assessing multiple pressures on aquatic ecosystems and understanding their combined impact on the ecological status is challenging, especially at the large scale, though crucial to the planning of effective policies. Here, for the first time, we quantify multiple human pressures and their relationship with the ecological status for all European rivers. We considered ecological data collected across Europe and pressures assessed by pan-European models, including pollution, hydrological and hydromorphological alterations. We estimated that in one third of EU’s territory rivers are in good ecological status. We found that better ecological status is associated with the presence of natural areas in floodplains, while urbanisation and nutrient pollution are important predictors of ecological degradation. We explored scenarios of improvement of rivers ecological status for Europe. Our results strengthen the need to halt urban land take, curb nitrogen pollution and maintain and restore nature along rivers.


He, H., Hu, E., Yu, J., Luo, X., Li, K., Liu, Z., Jeppesen, E. (2017). Does turbidity induced by crucian carp (Carassius auratus) limit phytoplankton growth? A mesocosm study. Environmental Science and Pollution Research 24(5), 5012-5018, http://dx.doi.org/10.1007/s11356-016-8247-z

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Does turbidity induced by crucian carp (Carassius auratus) limit phytoplankton growth? A mesocosm study

It is well established that benthivorous fish in shallow lakes can create turbid conditions that influence phytoplankton growth both positively, as a result of elevated nutrient concentration in the water column, and negatively, due to increased attenuation of light. The net effect depends upon the degree of turbidity induced by the benthivores. Stocked Carassius carassius dominate the benthivorous fish fauna in many nutrient-rich Chinese subtropical and tropical shallow lakes, but the role of the species as a potential limiting factor in phytoplankton growth is ambiguous. Clarification of this relationship will help determine the management strategy and cost of restoring eutrophic lakes in China and elsewhere. Our outdoor mesocosm experiment simulating the effect of high density of crucian carp on phytoplankton growth and community structure in eutrophic shallow lakes suggests that stocking with this species causes resuspension of sediment, thereby increasing light attenuation and elevating nutrient concentrations. However, the effect of light attenuation was insufficient to offset the impact of nutrient enhancement on phytoplankton growth, and significant increases in both phytoplankton biomass and chlorophyll a concentrations were recorded. Crucian carp stocking favored the dominance of diatoms and led to lower percentages (but not biomass) of buoyant cyanobacteria. The dominance of diatoms may be attributed to a competitive advantage of algal cells with high sedimentation velocity in an environment subjected to frequent crucian carp-induced resuspension and entrainment of benthic algae caused by the fish foraging activities. Our study demonstrates that turbidity induced by stocked crucian carp does not limit phytoplankton growth in eutrophic waters. Thus, removal of this species (and presumably other similar taxa) from subtropical or tropical shallow lakes, or suspension of aquaculture, is unlikely to boost phytoplankton growth, despite the resulting improvements in light availability.


He, H., Luo, X., Jin, H., Gu, J., Jeppesen, E., Liu, Z., Li, K. (2017). Effects of exposed artificial substrata on the competition between phytoplankton and benthic algae: Implications for shallow lake restoration. Water 9, 24, http://dx.doi.org/10.3390/w9010024

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Effects of exposed artificial substrata on the competition between phytoplankton and benthic algae: Implications for shallow lake restoration

Phytoplankton and benthic algae coexist in shallow lakes and the outcome of the competition between these two photoautotrophs can markedly influence water clarity. It is well established that exposed artificial substrate in eutrophic waters can remove nutrients and fine particles from the water column via the attached periphyton canopy. However, the effects of the introduction of artificial substrate on the competition between planktonic and benthic primary producers remain to be elucidated. We conducted a short-term outdoor mesocosm experiment to test the hypothesis that the nutrient and light changes induced by exposed artificial substrate (polythene nets) would benefit the benthic algae. Artificial substrate significantly reduced total nitrogen and phosphorus concentrations and water clarity improved, the latter due to the substrate-induced reduction of both organic and inorganic suspended solids. Consequently, as judged from changes in chlorophyll a (Chl-a) concentrations in water and sediment, respectively, exposed artificial substrate significantly reduced the phytoplankton biomass, while benthic algae biomass increased. Our results thus indicate that exposed artificial substrate may be used as a tool to re-establish benthic primary production in eutrophic shallow lakes after an external nutrient loading reduction, paving the way for a benthic-or a macrophyte-dominated system. Longer term and larger scale experiments are, however, needed before any firm conclusions can be drawn on this.


Iglesias, C., Meerhoff, M., Johanson, L. S., Gonzalez-Bergonzoni, I., Mazzeo, N., Pacheco, J. P., Teixeira de Mello, F., Goyenola, G., Lauridsen, T., Sondergard, M., Davidson, T., Jeppesen, E. (2017). Stable isotopes analysis confirms substantial differences between subtropical and temperate shallow lakes food webs. Hydrobiologia 784, 111-123, http://dx.doi.org/10.1007/s10750-016-2861-0

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Stable isotopes analysis confirms substantial differences between subtropical and temperate shallow lakes food webs

Differences in trophic web structure in otherwise similar ecosystems as a consequence of direct or indirect effects of ambient temperature differences can lead to changes in ecosystem functioning. Based on nitrogen and carbon stable isotope analysis, we compared the food-web structure in a series of subtropical (Uruguay, 30–35°S) and temperate (Denmark, 55–57°N) shallow lakes. The food-web length was on average one trophic position shorter in the subtropical shallow lakes compared with their temperate counterparts. This may reflect the fact that the large majority of subtropical fish species are omnivores (i.e., feed on more than one trophic level) and have a strong degree of feeding niche overlap. The shapes of the food webs of the subtropical lakes (truncated and trapezoidal) suggest that they are fuelled by a combination of different energy pathways. In contrast, temperate lake food webs tended to be more triangular, likely as a result of more simple pathways with a top predator integrating different carbon sources. The effects of such differences on ecosystem functioning and stability, and the connection with ambient temperature as a major underlying factor, are, however, still incipiently known.


Jeppesen E., Søndergaard, M. (2017). Lake Restoration and Management in a Climate Change Perspective: An introduction. Water 9, 122, http://dx.doi.org/10.3390/w9020122

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Lake Restoration and Management in a Climate Change Perspective: An introduction

Lakes all around the globe are under severe pressure due to an increasing anthropogenic impact from a growing population in a more developed world. Accordingly, today, many lakes are highly eutrophic and suffer from severe blooms of often toxic cyanobacteria and may become even more eutrophic in the future unless strong lake management actions are taken. Recent research has further shown that global warming and subsequent changes in water use will further exacerbate the eutrophication process in lakes. There is therefore a growing demand for lake restoration and insight into sustainable lake management. The measures to be taken, however, depend on the climate and other local conditions. This special issue addresses lake restoration and management with special emphasis on the restoration of eutrophicated lakes within a climate change perspective. The papers included collectively highlight that the ongoing climate change affects lake water quality by (1) changes in external and internal nutrient loading; (2) higher frequency of extreme events (such as hurricanes); (3) temperature‐induced changes in biota, biotic interactions; and (4) water level. Lower nutrient loading is therefore needed in a future warmer world to achieve the same ecological state as today. Several papers discuss lake restoration methods within a climate change perspective and show practical results, notably of various attempts of biomanipulation. Finally, some papers discuss the effects of other anthropogenic stressors and their interaction with climate.


Ren, L., He, D., Chen, Z., Jeppesen, E., Lauridsen, T. L., Søndergaard, M., Liu, Z., Wu, Q. L. (2017) Warming and nutrient enrichment in combination increase stochasticity and beta diversity of bacterioplanltopn assemblages across freshwater mesocosms, The ISME Journal 11(3), 613-625, http://dx.doi.org/10.1038/ismej.2016.159

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Warming and nutrient enrichment in combination increase stochasticity and beta diversity of bacterioplankton assemblages across freshwater mesocosms

The current climate warming and eutrophication are known to interactively threaten freshwater biodiversity; however, the interactive effects on lacustrine bacterioplankton diversity remain to be determined. Here, we analyzed the spring bacterioplankton community composition (BCC) in 24 outdoor, flow-through mesocosms (mimicking shallow lake environments) under 3 temperature scenarios and 2 nutrient regimes. Our results revealed that neither long-term warming (8.5 years) nor nutrient enrichment had significant effects on bacterioplankton alpha diversity, whereas long-term enhanced warming (elevated 50% above the IPCC A2 climate scenario) and nutrient enrichment in combination increased bacterioplankton beta diversity. We also found that BCC shifted significantly under enhanced warming and nutrient-enriched conditions towards decreased relative abundances of Actinobacteria, Bacteroidetes and Betaproteobacteria, whereas the percentages of Cyanobacteria, total rare phyla and unclassified phyla significantly increased. Null-model tests indicated that deterministic processes played a more important role than stochastic processes in determining BCC. However, the relative importance of stochasticity, primarily ecological drift, was enhanced and contributed to the increased beta diversity of BCC under enhanced warming and nutrient-enriched conditions. Overall, our study suggests that the synergetic effects of warming and nutrient enrichment may result in high variability in the composition of bacterioplankton communities in lacustrine water bodies.


Søndergaard, M., Lauridsen, T. L., Johansson, L. S., Jeppesen, E. (2017). Nitrogen or phosphorus limitation in lakes and its impact on phytoplankton biomass and submerged macrophyte covers. Hydrobiologia 9, online, http://dx.doi.org/10.1007/s10750-017-3110-x

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Nitrogen or phosphorus limitation in lakes and its impact on phytoplankton biomass and submerged macrophyte covers

We used data on nutrients, chlorophyll a (Chla) and submerged macrophyte cover from up to 817 Danish lakes to elucidate seasonal variations in nitrogen (N) and phosphorus (P) concentrations and to study the impact of N or its role in combination with P. In both deep and shallow lakes, we found marked seasonality in the ratio between total N and total P (TN:TP) and in the inorganic concentrations of nitrogen (DIN), indicating that N more easily becomes a limiting nutrient as summer proceeds. TN:TP reached its lowest values of <7 (by mass) in August in 25% of the shallow lakes. Chla generally related more strongly to TP than to TN, but at high TP concentrations TN explained more of the variability in Chla than TP. Macrophyte cover tended to decrease at increasing TN when TP was between 0.1 and 0.4 mg/l. At macrophyte cover above 20%, Chla was considerably lower compared with lakes with low macrophyte cover. We conclude that P is of key importance for the ecological quality of Danish lakes but that increased N concentrations, particularly in shallow lakes with moderate to high TP, may have significantly adverse effects on lake water quality and ecological status in summer.


Søndergaard, M., Lauridsen, T. L., Johansson, L. S., Jeppesen, E. (2017). Repeated fish removal to restore lakes: Case study Lake Væng, Denmark - Two biomanipulations during 30 years of monitoring. Water 9(1), online http://dx.doi.org/10.3390/w9010043

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Repeated fish removal to restore lakes: Case study Lake Væng, Denmark - Two biomanipulations during 30 years of monitoring

Biomanipulation by fish removal has been used in many shallow lakes as a method to improve lake water quality. Here, we present and analyse 30 years of chemical and biological data from the shallow and 16 ha large Lake Vaeng, Denmark, which has been biomanipulated twice with a 20-year interval by removing roach (Rutilus rutilus) and bream (Abramis brama). After both biomanipulations, Lake Vaeng shifted from a turbid, phytoplankton-dominated state to a clear, water macrophyte-dominated state. Chlorophyll a was reduced from 60–80 µg·L −1 to 10–30 µg·L −1 and the coverage of submerged macrophytes, dominated by Elodea canadensis, increased from <0.1% to 70%–80%. Mean summer total phosphorus was reduced from about 0.12 to 0.07 mg·L −1 and total nitrogen decreased from 1.0 to 0.4 mg·L −1. On a seasonal scale, phosphorus and chlorophyll concentrations changed from a summer maximum during turbid conditions to a winter maximum under clear conditions. The future of Lake Vaeng is uncertain and a relatively high phosphorus loading via the groundwater, and the accumulation of a mobile P pool in the sediment make it likely that the lake eventually will return to turbid conditions. Repeated fish removals might be a relevant management strategy to apply in shallow lakes with a relatively high external nutrient loading.


Tavşanoğlu, U.N, Šorf, M., Stefanidis, K., Brucet, S., Agasild, H., Boho, D., Scharfenberger, U., Beklioğlu, M., Hejzlar, J., Papastergiadou, E., Adrian, R., Angeler, D., Nõges, T., Çakıroğlu, A. I., Özen, A., Drakare, S., Søndergaard, M., Jeppesen, E. (2017). Effects of nutrient and water level changes on the composition and size structure of zooplankton communities under different climatic conditions: A Pan-European mesocosm experiment. Aquatic Ecology, online, http://dx.doi.org/10.1007/s10452-017-9615-6

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Effects of nutrient and water level changes on the composition and size structure of zooplankton communities under different climatic conditions: A Pan-European mesocosm experiment

Lentic ecosystems act as sentinels of climate change, and evidence exists that their sensitivity to warming varies along a latitudinal gradient. We assessed the effects of nutrient and water level variability on zooplankton community composition, taxonomic diversity and size structure in different climate zones by running a standardised controlled 6-months (May to November) experiment in six countries along a European north–south latitudinal temperature gradient. The mesocosms were established with two different depths and nutrient levels. We took monthly zooplankton samples during the study period and pooled a subsample from each sampling to obtain one composite sample per mesocosm. We found a significant effect of temperature on the community composition and size structure of the zooplankton, whereas no effects of water depth or nutrient availability could be traced. The normalised size spectrum became flatter with increasing temperature reflecting higher zooplankton size diversity due to higher abundance of calanoid copepods, but did not differ among depths or nutrient levels. Large-bodied cladocerans such as Daphnia decreased with temperature. Taxonomic diversity was positively related to size diversity, but neither of the two diversity measures demonstrated a clear pattern along the temperature gradient nor with nutrient and water levels. However, genus richness decreased at the warm side of the temperature gradient. Our experiment generally supports recent empirically based findings that a continuing temperature increase may result in lower genus richness and lower abundance of large-sized zooplankton grazers, the latter likely resulting in reduced control of phytoplankton.


Teichert, N., Pasquaud, S., Borja, A., Chust, G., Uriarte, A., Lepage, M. (2017). Living under stressful conditions: Fish life history strategies across environmental gradients in estuaries. Estuarine, Coastal and Shelf Science 188, 18-26, http://dx.doi.org/10.1016/j.ecss.2017.02.006

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Living under stressful conditions: Fish life history strategies across environmental gradients in estuaries

The life history strategies of fishes can be defined by specific combinations of demographic traits that influence species performances depending on environmental features. Hence, the constraints imposed by the local conditions restrict the range of successful strategies by excluding species poorly adapted. In the present study, we compared the demographic strategies of fish caught in 47 estuaries of the North East Atlantic coast, aiming to determine the specific attributes of resident species and test for changes in trait associations along the environmental gradients. Eight demographic traits were considered to project our findings within a conceptual triangular model, composed on three endpoint strategies: (i) periodic (large size, long generation time, high fecundity); (ii) opportunistic (small size, short generation time, high reproductive effort); and (iii) equilibrium (low fecundity, large egg size, parental care). We demonstrated that various life history strategies co-exist in estuaries, but equilibrium species were scarce and restricted to euhaline open-water. Resident species form a specialised assemblage adapted to high spatiotemporal variability of estuarine conditions, i.e. opportunistic attributes associated with parental care. Even with these singular attributes, our findings revealed changes in distribution of resident species across the estuarine gradients linked to their life history traits. Among other patterns, the diversity of life history strategies significantly decreased from euhaline to oligohaline areas and along gradient of human disturbances. These trends were associated with a convergence of species traits toward short generation times, suggesting that long-lived species with late maturation are more severely impacted by disturbance and environmental stress.


Woolway, R. I., Meinson, P., Nõges, P., Jones, I. D., Laas, A. (2017). Atmospheric stilling leads to prolonged thermal stratification in a large shallow polymictic lake. Climatic Change 141(4), 759-773, http://dx.doi.org/10.1007/s10584-017-1909-0

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Atmospheric stilling leads to prolonged thermal stratification in a large shallow polymictic lake

To quantify the effects of recent and potential future decreases in surface wind speeds on lake thermal stratification, we apply the one-dimensional process-based model MyLake to a large, shallow, polymictic lake, Võrtsjärv. The model is validated for a 3-year period and run separately for 28 years using long-term daily atmospheric forcing data from a nearby meteorological station. Model simulations show exceptionally good agreement with observed surface and bottom water temperatures during the 3-year period. Similarly, simulated surface water temperatures for 28 years show remarkably good agreement with long-term in situ water temperatures. Sensitivity analysis demonstrates that decreasing wind speeds has resulted in substantial changes in stratification dynamics since 1982, while increasing air temperatures during the same period had a negligible effect. Atmospheric stilling is a phenomenon observed globally, and in addition to recent increases in surface air temperature, needs to be considered when evaluating the influence of climate change on lake ecosystems.


Zhang, W., Jeppesen, E., Wang, M., Xu, X., Wang, L. (2017). Allelopathic effect boosts Chrysosporum ovalisporum dominance in summer at the expense of Microcystis panniformis in a shallow coastal water body. Environmental Science and Pollution Research 24(5), 4666-4675, http://dx.doi.org/10.1007/s11356-016-8149-0

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Allelopathic effect boosts Chrysosporum ovalisporum dominance in summer at the expense of Microcystis panniformis in a shallow coastal water body.

The increased occurrence of harmful cyanobacterial species and, with this, higher frequency of cyanobacteria blooms, closely associated with eutrophication and climate change, have attracted increasing attention worldwide. However, competition mechanisms between the different bloom-forming cyanobacteria species remain to be elucidated. In this paper, for the first time, the allelopathic effect of the cyanobacterium Chrysosporum ovalisporum on the cyanobacterium Microcystis panniformis is reported. The results of our study conducted in a Chinese shallow coastal water body demonstrated that the biomass of M. panniformis was relatively low during the C. ovalisporum blooming period. Co-cultivation of a C. ovalisporum strain with a M. panniformis strain showed strong inhibition of the growth of M. panniformis but stimulation of C. ovalisporum. Thus, filtrate of C. ovalisporum culture had a strong inhibitory effect on the performance of M. panniformis by decreasing the maximum optical quantum yield (Fv/Fm), the electron transport rate (ETR) of PS II and the onset of light saturation (Ik) and by increasing the alkaline phosphatase (ALP) activity and superoxide dismutase (SOD) activity of M. panniformis. Our results suggest that the interspecific allelopathic effect plays an important role in the competition between different cyanobacteria species. We foresee the importance of C. ovalisporum to intensify in a future warmer world, not least in small- to medium-sized, warm and high conductivity coastal water bodies.


Zhang X., Tang, Y., Jeppesen E., Liu, Z. (2017). Biomanipulation-induced reduction of sediment phosphorus release in a tropical shallow lake. Hydrobiologia, online, http://dx.doi.org/10.1007/s10750-016-3079-x

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Biomanipulation-induced reduction of sediment phosphorus release in a tropical shallow lake

Biomanipulation via fish regulation combined with submerged plant introduction is an effective measure to restore eutrophic shallow lakes. Improved water quality and clarity promote growth of benthic algae, which with submerged plants may limit sediment phosphorus (P) release, thereby reinforce lake recovery. Our study sought to evaluate the effect of such a biomanipulation on water quality, benthic algal development and sediment P release in a shallow, tropical lake by (1) comparing porewater and lake water quality, light intensity and benthic algal development in restored and unrestored sections; (2) conducting a 32P radiotracer experiment to track P release from sediment cores sampled from both sections. The biomanipulation led to lower total P, total dissolved P, and soluble reactive P concentrations in lake water, lower phytoplankton biomass, and increased light intensity at sediment surface, stimulating benthic algal development. Moreover, sediment 32P release was lower in the restored than unrestored section. Concurrently, dissolved oxygen levels in upper layers of the sediment cores were higher in the restored section. Our study indicates that the biomanipulation improved water quality and enhanced growth of benthic algae, thereby reducing sediment P release, which may be one of the main mechanisms to create successful restoration.


Zhou, Y., Shi, K., Liu, X., Jeppesen, E., Zhang, Y., Zhou, Q., Wu, H., Tang, X. Zhu, G. (2017) Fluorescence peak integration ratio IC:IT as a new potential real-time tracer differentiating dissolved organic matter of allochthonous and autochthonous origin in waters, Science of the Total Environment (online), http://dx.doi.org/10.1016/j.scitotenv.2016.08.196

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Fluorescence peak integration ratio IC:IT as a new potential indicator tracing the compositional changes in chromophoric dissolved organic matter

The present study demonstrates that the ratio of fluorescence integration of peak C to peak T (IC:IT) can be used as an indicator tracing the compositional dynamics of chromophoric dissolved organic matter (CDOM). CDOM absorption and fluorescence spectroscopy and stable isotope δ13C were determined on a seasonal basis in seventeen Chinese inland waters as well as in a series of mixing and photodegradation experiments in the lab. A strong positive linear correlation was recorded between IC:IT and the ratio of terrestrial humic-like C1 to tryptophan-like C4 (C1:C4) derived by parallel factor analysis. The r2 for the linear fitting between IC:IT and C1:C4 (r2 = 0.80) was notably higher than between C1:C4 and other indices tested, including the ratio of CDOM absorption at 250 nm to 365 nm, i.e. a(250):a(365) (r2 = 0.09), spectral slope (S275–295) (r2 = 0.26), spectral slope ratio (SR) (r2 = 0.31), the humification index (HIX) (r2 = 0.47), the recent autochthonous biological contribution index (BIX) (r2 = 0.27), and a fluorescence index (FI370) (r2 = 0.07). IC:IT exhibited larger variability than the remaining six indices and a closer correlation with stable isotope δ13C than that observed for a(250):a(365), S275–295, SR, FI370, and BIX during field campaigns. Confirming our field observations, significant correlations were recorded between IC:IT and the remaining six indices, and IC:IT also demonstrated notably larger variability than the six other indices during our wastewater addition experiment. Compared with HIX, eutrophic water addition and photobleaching substantially decreased IC:IT but had no pronounced effect on a(250):a(365), S275–297, SR, FI370, and BIX, further suggesting that IC:IT is the most efficient indicator of the CDOM compositional dynamics.


Zhou, Y., Yao, X., Zhang, Y., Shi, K., Zhang, Y., Jeppesen, E., Gao, G., Zhu, G., Qin, B. (2017). Potential rainfall-intensity and pH-driven shifts in the apparent fluorescent composition of dissolved organic matter in rainwater. Environmental Pollution 224, 638-648, http://dx.doi.org/10.1016/j.envpol.2017.02.048

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Potential rainfall-intensity and pH-driven shifts in the apparent fluorescent composition of dissolved organic matter in rainwater

Perturbations of rainwater chromophoric dissolved organic matter (CDOM) fluorescence induced by changes in rainfall intensity and pH were investigated by field observations and laboratory pH titrations. Microbial humic-like fluorophores dominated the rainwater CDOM pool, followed by tryptophan-like and tyrosine-like substances. Increased rainfall intensity had notable dilution effects on all six fluorescent components (C1-C6) identified using parallel factor (PARAFAC) analysis, the effect being especially pronounced for the microbial humic-like C1, tryptophan-like C3, and tyrosine-like C5. The results also indicated that increasing pH from 7 to 9 led to decreased fluorescence intensity (Fmax) of all the six components, while a pH increase from 5 to 7, resulted in increasing Fmax of terrestrial humic-like C2, tyrosine-like C5, and tryptophan-like C6 and decreasing microbial humic-like C1, tryptophan-like C3, and fulvic-like C4. Two-dimensional correlation spectroscopy (2D-COS) demonstrated that synchronous fluorescence responded first to pH modifications at fulvic-like wavelength (λEx/λEm = ∼316/416 nm), followed by tyrosine-like wavelength (λEx/λEm = ∼204/304 nm), tryptophan-like wavelength (λEx/λEm = ∼226/326 nm), microbial humic-like wavelength (∼295/395 nm), and finally terrestrial humic-like wavelength (∼360/460 nm). Our results suggest that a decrease in areas affected by acid rain in South China occurring at present may possibly result in apparent compositional changes of CDOM fluorescence. The decreased rainfall in South-West China and increased rainfall in North-West China during the past five decades may possibly accordingly result in increased and decreased Fmax of all the six components identified in South-West and North-West China, respectively.


2016

Alahuhta, J., Hellsten, S., Kuoppala, M., Riihimäki, J. (2016). Regional and local determinants of macrophyte community composition in high-latitude lakes in Finland. Hydrobiologia, online, http://dx.doi.org/10.1007/s10750-016-2843-2

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Regional and local determinants of macrophyte community compositions in high-latitude lakes of Finland

Species distributions are structured by regional and local determinants, which operate at multiple spatial and temporal scales. The purpose of our work was to distinguish the relative roles of local variables, climate, geographical location and post glaciation condition (i.e. delineation between supra- and subaquatic lakes during the post-glacial Anculys Lake) in explaining variation in macrophyte community composition of all taxa, helophytes and hydrophytes. In addition, we investigated how these four explanatory variable groups affected macrophyte strategy groups based on Grime’s classification. Using partial linear regression and variation partitioning, we found that macrophyte communities are primarily filtered by local determinants together with regional characteristics at the studied spatial scale. We further evidenced that post glaciation condition indirectly influenced on local water quality variables, which in turn directly contributed to the macrophyte communities. We thus suggest that regional determinants interact with local-scale abiotic factors in explaining macrophyte community patterns and examining only regional or local factors is not sufficient for understanding how aquatic macrophyte communities are structured locally and regionally.


Alahuhta, J., Aroviita, J. (2016) Quantifying the relative importance of natural variables, human disturbance and spatial processes in ecological status indicators of boreal lakes, Ecological Indicators 63, 240–248, http://dx.doi.org/10.1016/j.ecolind.2015.12.003

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Quantifying the relative importance of natural variables, human disturbance and spatial processes in ecological status indicators of boreal lakes

Spatial processes are increasingly associated with species distributions in freshwaters. However, these processes are usually neglected in bioassessment techniques, which may introduce uncontrolled variation in ecological indicators used to express human disturbance. We used partial linear regression to quantify the relative importance of natural variables, human disturbance and spatial variables in structuring variation in boreal lake status indicators based on six biological indicator groups (phytoplankton, macrophytes, diatoms, littoral and profundal macroinvertebrates and fish). We found that, of the pure fractions, human disturbance explained most variation (7-32%) of the Ecological Quality Ratios (EQRs) for all groups, with the exception of littoral macroinvertebrate metric, which was most controlled by natural and spatial variables (15% and 16%, respectively). In addition, pure fractions of natural and spatial variables and joint fractions of different explanatory variable groups structured all biological metrics to various degrees. Phytoplankton, diatom and profundal macroinvertebrate EQRs responded purest to human disturbance but only weakly to pure natural or spatial variation. Our work demonstrates that spatial processes and spatial structuring of the environment can bias bioassessment techniques and hinder the detection of human impact. Thus, it is important to acknowledge spatial autocorrelation, context of metacommunity dynamics, species dispersal traits and variable spatial extent when defining reference conditions and bioassessment techniques for different biological groups. More research is needed to better understand the relative role of spatial processes on ecological metrics originated from different freshwater ecosystems. To this end, our work provides an example of how sources of variation can be identified to increase accuracy in freshwater bioassessment.


Alnøe, A. B., Riis, T., Baattrup-Pedersen, A. (2016). Comparison of metabolic rates among macrophyte and nonmacrophyte habitats in streams. Freshwater Science 35, 909-921, http://dx.doi.org/10.1086/687842

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Comparison of metabolic rates among macrophyte and nonmacrophyte habitats in streams

Little is known about the relative contribution of different stream habitats to reach-scale metabolism. We measured in situ metabolism in sand, gravel, stone, and macrophyte habitats to compare metabolic rates among these habitat types and to compare habitat-weighted measurements with reach-scale measurements. We used open-bottom chambers in sand, gravel, and macrophyte habitats and closed-bottom chambers in stones, and we estimated reach-scale metabolism from 2-station O2 budgets. Macrophyte habitats had a significantly higher gross primary production (GPP) and community respiration (CR) than stone, gravel, and sand habitats. A large part of this difference was associated with epiphytic biofilm: 28% of net ecosystem production (NEP), 20% of CR, and 24% of GPP. Macrophyte habitats contributed proportionally more to reach-scale metabolism than did the other habitat types. Forty-one percent of reach-scale NEP, 60% of ecosystem respiration (ER), and 50% of GPP were associated with this habitat type even though only 14% of the reach was covered by macro-phytes. We found significant linear relationships between GPP and CR and the amount of autotrophic biomass in the streams. The rates reported in 11 literature studies fit into our observed relationships, showing the generality of our findings. The rates we obtained expand the range of reported metabolic values in relation to auto-trophic biomass for both low and high biomass. The importance of macrophyte habitat can be ascribed to the macrophytes themselves, the associated epiphytic biofilm, and the fine organic material trapped in the dense stands. We conclude that besides having an effect on the structural elements in streams, macrophytes contribute significantly to stream ecosystem functions.


Baattrup-Pedersen, A., Göthe, E., Riis, T., O'Hare, M. T. (2016) Functional trait composition of aquatic plants can serve to disentangle multiple interacting stressors in lowland streams, Sciene of The Total Environment 543, 230-238, http://dx.doi.org/10.1016/j.scitotenv.2015.11.027

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Functional trait composition of aquatic plants can serve to disentangle multiple interacting stressors in lowland streams

Historically, close attention has been paid to negative impacts associated with nutrient loads to streams and rivers, but today hydromorphological alterations are considered increasingly implicated when lowland streams do not achieve good ecological status. Here, we explore if trait-abundance patterns of aquatic plants change along gradients in hydromorphological degradation and eutrophication in lowland stream sites located in Denmark. Specifically, we hypothesised that: i) changes in trait-abundance patterns occur along gradients in hydromorphological degradation and ii) trait-abundance patterns can serve to disentangle effects of eutrophication and hydromorphological degradation in lowland streams reflecting that the mechanisms behind changes differ. We used monitoring data from a total of 147 stream reaches with combined data on aquatic plant species abundance, catchment land use, hydromorphological alterations (i.e. planform, cross section, weed cutting) and water chemistry parameters. Traits related to life form, dispersal, reproduction and survival together with ecological preference values for nutrients and light (Ellenberg N and L) were allocated to 41 species representing 79% of the total species pool. We found clear evidence that habitat degradation (hydromorphological alterations and eutrophication) mediated selective changes in the trait-abundance patterns of the plant community. Specific traits could distinguish hydromorphological degradation (free-floating, surface; anchored floating leaves; anchored heterophylly) from eutrophication (free-floating, submerged; leaf area). We provide a conceptual framework for interpretation of how eutrophication and hydromorphological degradation interact and how this is reflected in trait-abundance patterns in aquatic plant communities in lowland streams. Our findings support the merit of trait-based approaches in biomonitoring as they shed light on mechanisms controlling structural changes under environmental stress. The ability to disentangle several stressors is particularly important in lowland stream environments where several stressors act in concert since the impact of the most important stressor can be targeted first, which is essential to improve the ecological status.


Boll, T., Levi, E. E., Bezirci, G., Özuluğ, M., Tavsanoğlu, Ü. N., Çakıroğlu,  A. I., Özcan, S., Brucet, S., Jeppesen, E. & Beklioğlu, M.  (2016) Fish assemblage and diversity in lakes of western and central Turkey - role of geo-climatic and environmental gradients, Hydrobiologia 771, 31-44, http:/www.dx.doi.org/10.1007/s10750-015-2608-3"

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Fish assemblage and diversity in lakes of western and central Turkey: role of geo-climatic and other environmental variables

We conducted a fish survey in 40 lakes in western and central Turkey. Fifty species (one to eleven per lake) were recorded, including eighteen endemic and seven alien species. We investigated which local geo-climatic and other environmental variables shaped the fish assemblages. Altitude and temperature turned out to be the most important factors for total species richness as well as richness of omnivorous and zooplanktivorous species and the Shannon–Wiener diversity index, with more species and higher diversity occurring in the warmer lowland lakes. Altitude may affect the fish assemblage directly through dispersal limitation or indirectly by creating a gradient in temperature with which it was strongly correlated. Cyprinidae was the most species-rich and widespread family. Atherinidae, Gobiidae, and Mugilidae (families of marine origin) were mainly found in the lowland regions, while Salmonidae exclusively appeared in the high-altitude lakes. The presence of widely distributed translocated native and alien species revealed a large human impact on the fish assemblages, potentially threatening the rich endemic fish fauna in lakes in this region.


Bondar-Kunze, E., Maier, S., Schönauer, D., Bahl, N., Hein, T. (2016) Antagonistic and synergistic effects on a stream periphyton community under the influence of pulsed flow velocity increase and nutrient enrichment, Science of The Total Environment 573, 594-602, http://dx.doi.org/10.1016/j.scitotenv.2016.08.158

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Antagonistic and synergistic effects on a stream periphyton community under the influence of pulsed flow velocity increase and nutrient enrichment

Aquatic ecosystems are generally affected by multiple stressors, and therefore, analysing single stressor responses is not appropriate to evaluate the whole range of effects on these ecosystems. We assessed the interaction effects of two strong stressors (higher flow velocity due to e.g. daily hydropeaking) and nutrient enrichment for an oligotrophic stream periphyton community. As periphyton has a rapid reproduction rate and very short life cycles, it can therefore be expected to reflect short-term impacts and sudden changes/disturbances in the environment. We measured biomass development, algal group distribution and photosynthesis efficiency during a time period of 33 days in an experimental flume setting in Lunz am See (Austria). We conducted the experiment with two treatments (no hydropeaking and hydropeaking) and three nutrient enrichments (nitrate, phosphate and nitrate + phosphate enrichment) and control (no nutrient addition). The results showed a significant lower biomass development in the hydropeaking treatment (HP), compared to the no-hydropeaking treatment (NHP) in a later successional stage (day 33). Nutrient subsidy effects were not observed, because the biomass development (chlorophyll-a) of periphyton was highly diminished through the pulsed flow velocity increase. Also a negative synergistic interaction (more negative than predicted additively) was observed. Our study confirmed for periphyton communities that for different algal groups and functional guilds the same multiple stressor combination can be detrimental for one species group (e.g. chlorophyta) while beneficial for another (e.g. diatoms). We conclude for multiple stressor studies to consider the successional stage and community composition, when estimating the interaction effects of these stressors.


Borza, P., Huber, T., Leitner, P., Remund, N., Graf, W. (2016). Current velocity shapes co-existence patterns among invasive Dikerogammarus species. Freshwater Biology, online, http://dx.doi.org/10.1111/fwb.12869

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Current velocity shapes co-existence patterns among invasive Dikerogammarus species

RFacilitative interactions among co-evolved representatives of the endemic Ponto-Caspian fauna are regarded as a major factor of their invasion success. Nevertheless, the most renowned examples represent interactions between different trophic levels or functional groups, while ecologically similar species can be expected to show competition-based niche partitioning. Here, we test for differences in the realized niche of three invasive Dikerogammarus species (Crustacea: Gammaridae) in their co-occurring range. We sampled multiple habitats within sites distributed along the River Danube to test whether some environmental variables could reveal spatial niche differentiation among the three species of Dikerogammarus, and if so, to test a predictive model outside the zone of co-occurrence. Spatial niche differentiation was present among the species, primarily determined by current velocity (and associated substrate preference), likely reflecting a stress tolerance–competitive ability trade-off. Suspended matter concentration was also relevant, suggesting food resources (through filter feeding) might represent another important niche axis, somewhat loosening the terms of co-existence between D. haemobaphes and the other two species. Environmental variables could effectively explain the absence of D. bispinosus in the Lower Danube, implying that the co-existence of the three species is possible only along a sufficiently wide current velocity gradient, and the observed turnovers are the result of niche expansion in the absence of the stronger competitor. Hence, differences in invasion success may be attributed to a stress tolerance–competitive ability trade-off. Our results suggest the advantage of D. villosus is attributable to its competitive dominance, allowing it to monopolize lentic and/or structured habitats, which represents a fortunate pre-adaptation to anthropogenic alterations of aquatic ecosystems. The presence of D. villosus does not greatly affect the expansion of D. haemobaphes; however, the exclusion of D. bispinosus from lentic habitats by D. villosus probably strongly limits its potential to spread by active dispersal.


Bowes, M. J., Loewenthal, M., Read, D. S., Hutchins, M. G., Prudhomme, C., Armstrong, L. K., Harman, S. A., Wickham, H. D., Gozzard E., Carvalho, L. (2016). Identifying multiple stressor controls on phytoplankton dynamics in the River Thames (UK) using high-frequency water quality data. Science of the Total Environment 569-570, 1489-1499, http://dx.doi.org/10.1016/j.scitotenv.2016.06.239

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Identifying multiple stressor controls on phytoplankton dynamics in the River Thames (UK) using high-frequency water quality data

River phytoplankton blooms can pose a serious risk to water quality and the structure and function of aquatic ecosystems. Developing a greater understanding of the physical and chemical controls on the timing, magnitude and duration of blooms is essential for the effective management of phytoplankton development. Five years of weekly water quality monitoring data along the River Thames, southern England were combined with hourly chlorophyll concentration (a proxy for phytoplankton biomass), flow, temperature and daily sunlight data from the mid-Thames. Weekly chlorophyll data was of insufficient temporal resolution to identify the causes of short term variations in phytoplankton biomass. However, hourly chlorophyll data enabled identification of thresholds in water temperature (between 9 and 19°C) and flow (<30m(3)s(-1)) that explained the development of phytoplankton populations. Analysis showed that periods of high phytoplankton biomass and growth rate only occurred when these flow and temperature conditions were within these thresholds, and coincided with periods of long sunshine duration, indicating multiple stressor controls. Nutrient concentrations appeared to have no impact on the timing or magnitude of phytoplankton bloom development, but severe depletion of dissolved phosphorus and silicon during periods of high phytoplankton biomass may have contributed to some bloom collapses through nutrient limitation. This study indicates that for nutrient enriched rivers such as the Thames, manipulating residence time (through removing impoundments) and light/temperature (by increasing riparian tree shading) may offer more realistic solutions than reducing phosphorus concentrations for controlling excessive phytoplankton biomass.


Branco, P., Santos, J. M., Amaral, S., Romao, F., Pinheiro, A. N., Ferreira, M. T. (2016). Potamodromous fish movements under multiple stressors: Connectivity reduction and oxygen depletion. Science of the Total Environment 572, 520-525, http://dx.doi.org/10.1016/j.scitotenv.2016.08.070

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Potamodromous fish movements under multiple stressors: Connectivity reduction and oxygen depletion

Rivers are impacted by multiple stressors that can interact to create synergistic, additive or antagonistic effects, but experimental studies on fish encompassing more than one stressor are seldom found. Thus, there is the need to study stressors through multifactorial approaches that analyse the impact of fish exposure to multiple stressors and evaluate fish sensitivity to stressor combinations. Some of the most common impacts to Mediterranean rivers are of two natures: i) water abstraction and ii) diffuse pollution. Therefore, the present study aims at studying the responses of potamodromous fish facing combinations of: 1) a primary stressor (two levels of connectivity reduction due to water scarcity), and 2) a secondary stressor (three levels of oxygen depletion due to increase organic load - of anthropogenic nature). Schools of five wild fish from a cyprinid species (Luciobarbus bocagei) were placed in a flume, equipped with see-through sidewalls to allow for behavioural analysis, and subjected to different combinations of the stressors. Results show that at the unconnected level the primary stressor (lack of connectivity) overrode the effect of the secondary stressor (oxygen depletion), but when connectivity existed oxygen depletion caused a reduction of fish movements with decreasing oxygen concentrations. This multifactorial study contributes to improved prediction of fish responses upon actual or projected pressure scenarios.


Bruno, D., Gutiérrez-Cánovas, T., Sánchez-Fernández, D., Velasco, J., Nilsson, C. (2016) Impacts of environmental filters on funcational redundancy in riparian vegetation, Jurnal of Applied Ecology 53, 846-855, http://dx.doi.org/10.1111/1365-2664.12619

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Impacts of environmental filters on funcational redundancy in riparian vegetation

Understanding and predicting ecosystem responses to multiple environmental pressures is a long-standing interest in ecology and environmental management. However, few studies have examined how the functional features of freshwater biological communities vary along multiple gradients of environmental stress. Furthermore, modelling these functional features for a whole river network constitutes a strong potential basis to improve ecosystem management. 2.We explored how functional redundancy of biological communities (FR, a functional feature related to the stability, resistance and resilience of ecosystems) responds to single and multiple environmental filters. We compared these responses with those of functional richness, evenness and divergence. We used riparian vegetation of a Mediterranean basin, and three of the main environmental filters affecting freshwater communities in such regions, i.e. drought, flow regulation and agricultural intensity, thus considering the potential effect of natural environmental variability. We also assessed the predictability of FR and estimated it for the entire river network. 3.We found that all functional measures decreased with increasing environmental filter intensity. However, FR was more sensitive to single and multiple environmental filters compared to other functional measures. The best-fitting model explained 59% of the FR variability and included agriculture, drought and flow regulation and the pairwise interactions of agriculture with drought and flow regulation. The parameters of the FR models differed from null model expectations reflecting a non-random decline along stress gradients. 4.Synthesis and applications. We found non-random detrimental effects along environmental filters for riparian functional redundancy (FR, the most sensitive functional index), meaning that increased stress could jeopardize stability, resistance and resilience of these systems. In general, agriculture caused the greatest impact on FR and functional diversity measures, being the most important stressor for riparian functionality in the study area. Temporary streams flowing through an agricultural, regulated basin had reduced values of FR, whereas the free-flowing medium-sized, perennial water courses flowing through unaltered sub-basins displayed higher values of FR and potentially greater stability against human impacts. All these findings along with the predicted basin-wide variation of FR can assist environmental managers in improving monitoring and ecosystem management. This article is protected by copyright. All rights reserved.


Bruno, D., Gutiérrez-Cánovas, T., Velasco, J., Sánchez-Fernández, D.(2016) Functional redundancy as a tool for bioassessment: A test using riparian vegetation(in press), http://dx.doi.org/10.1016/j.scitotenv.2016.05.186

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Functional redundancy as a tool for bioassessment: A test using riparian vegetation

There is an urgent need to track how natural systems are responding to global change in order to better guide management efforts. Traditionally, taxonomically based metrics have been used as indicators of ecosystem integrity and conservation status. However, functional approaches offer promising advantages that can improve bioassessment performance. In this study, we aim to test the applicability of functional redundancy (FR), a functional feature related to the stability, resistance and resilience of ecosystems, as a tool for bioassessment, looking at woody riparian communities in particular. We used linear mixed-effect models to investigate the response of FR and other traditional biomonitoring indices to natural (drought duration) and anthropogenic stress gradients (flow regulation and agriculture) in a Mediterranean basin. Such indices include species richness, a taxonomic index, and the Riparian Quality Index, which is an index of ecological status. Then, we explored the ability of FR and the other indices to discriminate between different intensities of human alteration. FR showed higher explanatory capacity in response to multiple stressors, although we found significant negative relationships between all the biological indices (taxonomic, functional and ecological quality) and stress gradients. In addition, FR was the most accurate index to discriminate among different categories of human alteration in both perennial and intermittent river reaches, which allowed us to set threshold values to identify undisturbed (reference condition), moderately disturbed and highly disturbed reaches in the two types of river. Using these thresholds and the best-fitting model, we generated a map of human impact on the functional redundancy of riparian communities for all the stretches of the river network. Our results demonstrate that FR presents clear advantages over traditional methods, which suggests that it should be part of the biomonitoring toolbox used for environmental management so as to obtain better predictions of ecosystem response to environmental changes.


Bussi, G., Whitehead, P. G., Bowes, M. J., Read, D. S., Prudhomme, C., Dadson, S. J. (2016). Impacts of climate change, land-use change and phosphorus reduction on phytoplankton in the River Thames (UK). Science of the Total Environment 572, 1507-1519, http://dx.doi.org/10.1016/j.scitotenv.2016.02.109

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Impacts of climate change, land-use change and phosphorus reduction on phytoplankton in the River Thames (UK)

Potential increases of phytoplankton concentrations in river systems due to global warming and changing climate could pose a serious threat to the anthropogenic use of surface waters. Nevertheless, the extent of the effect of climatic alterations on phytoplankton concentrations in river systems has not yet been analysed in detail. In this study, we assess the impact of a change in precipitation and temperature on river phytoplankton concentration by means of a physically-based model. A scenario-neutral methodology has been employed to evaluate the effects of climate alterations on flow, phosphorus concentration and phytoplankton concentration of the River Thames (southern England). In particular, five groups of phytoplankton are considered, representing a range of size classes and pigment phenotypes, under three different land-use/land-management scenarios to assess their impact on phytoplankton population levels. The model results are evaluated within the framework of future climate projections, using the UK Climate Projections 09 (UKCP09) for the 2030s. The results of the model demonstrate that an increase in average phytoplankton concentration due to climate change is highly likely to occur, with the magnitude varying depending on the location along the River Thames. Cyanobacteria show significant increases under future climate change and land use change. An expansion of intensive agriculture accentuates the growth in phytoplankton, especially in the upper reaches of the River Thames. However, an optimal phosphorus removal mitigation strategy, which combines reduction of fertiliser application and phosphorus removal from wastewater, can help to reduce this increase in phytoplankton concentration, and in some cases, compensate for the effect of rising temperature.


Cavalli, G., Baattrup-Pedersen, A. & Riis, T. (2016) Nutrient availability and nutrient use efficiency in plants growing in the transition zone between land and water, Plant Biology 18, 301-306, http://dx.doi.org/10.1111/plb.12397

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Nutrient availability and nutrient use efficiency in plants growing in the transition zone between land and water

The transition zone between terrestrial and freshwater habitats is highly dynamic, with large variability in environmental characteristics. Here, we investigate how these characteristics influence the nutritional status and performance of plant life forms inhabiting this zone. Specifically, we hypothesised that: (i) tissue nutrient content differs among submerged, amphibious and terrestrial species, with higher content in submerged species; and (ii) PNUE gradually increases from submerged over amphibious to terrestrial species, reflecting differences in the availability of N and P relative to inorganic C across the land-water ecotone. We found that tissue nutrient content was generally higher in submerged species and C:N and C:P ratios indicated that content was limiting for growth for ca. 20% of plant individuals, particularly those belonging to amphibious and terrestrial species groups. As predicted, the PNUE increased from submerged over amphibious to terrestrial species. We suggest that this pattern reflects that amphibious and terrestrial species allocate proportionally more nutrients into processes of importance for photosynthesis at saturating CO2 availability, i.e. enzymes involved in substrate regeneration, compared to submerged species that are acclimated to lower availability of CO2 in the aquatic environment. Our results indicate that enhanced nutrient loading may affect relative abundance of the three species groups in the land-water ecotone of stream ecosystems. Thus, species of amphibious and terrestrial species groups are likely to benefit more from enhanced nutrient availability in terms of faster growth compared to aquatic species, and that this can be detrimental to aquatic species growing in the land-water ecotone, e.g. Ranunculus and Callitriche. © 2015 German Botanical Society and The Royal Botanical Society of the Netherlands.


Çakiroğlu, A.I., Levi, E. E., Tavşanoğlu, N., Bezirci,G., Erdoğan, Ş., Filiz, N., Andersen, T. J., Davidson, T. A., Jeppesen, E. & Beklioğlu, M. (2016) Inferring past environmental change of three Turkish shallow lakes from community changes of sub-fossil cladocera, Hydrobiologia 778, 295-312, http://dx.doi.org/10.1007/s10750-015-2581-x

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Inferring past environmental changes in three Turkish lakes from sub-fossil Cladocera

Cladocerans are increasingly used in palaeolimnological studies as their community composition is sensitive to both anthropogenic and natural forces in lakes. We present the results of a palaeolimnological investigation of three Turkish shallow lakes located in cold dry steppe and semi-dry Mediterranean climatic regions. The aim was to elucidate historical changes in environmental conditions by analysing sub-fossil cladocerans in 210Pb-dated sediment cores. Sub-fossil cladoceran remains from the surface sediment of 40 Turkish lakes were analysed to examine the environmental factors that most correlated with variation in the cladoceran assemblage. Redundancy analysis showed that salinity, macrophyte abundance, fish density, depth and total phosphorus were the most correlated with change in cladoceran assemblage composition with eigenvalues for the first and the second axes being λ 1 = 0.312 and λ 2 = 0.061, respectively. Sedimentary cladoceran assemblages from three cores were placed passively within the framework of the surface sediment ordination. The results reveal a prevalent impact of salinity, fish abundance and water level changes from the past to present. Thus, using cladoceran-based inferences, we traced key environmental changes related to variation in climate change, restoration and water level regulation over the last century.


Chen, J., Cao, T., Zhang, X., Xi, Y., Ni, L., Jeppesen, E. (2016). Differential photosynthetic and morphological adaptations to low light affect depth distribution of two submersed macrophytes in lakes, Scientific Reports 6 (E34028), 1-9, http://dx.doi.org/10.1038/srep34028

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Differential photosynthetic and morphological adaptations to low light affect depth distribution of two submersed macrophytes in lakes

To evaluate the relative importance of photosynthetic versus morphological adaptations of submersed macrophytes to low light intensity in lakes, rapid light curves (RLCs), morphological parameters, relative growth rate (RGR), clonal reproduction and abundance of two submersed macrophytes (Potamogeton maackianus and Vallisneria natans) were examined under 2.8%, 7.1%, 17.1% and 39.5% ambient light in a field and outdoor experimental study. The plants increased their initial slope of RLCs (α) and decreased their minimum saturating irradiance (Ek) and maximum relative electron transport rate (ETRm) of RLCs under low light stress, but V. natans was more sensitive in RLCs than P. maackianus. Accordingly, the RGR, plant height and abundance of P. maackianus were higher in the high light regimes (shallow water) but lower in the low light regimes than those of V. natans. At the 2.8% ambient light, V. natans produced ramets and thus fulfilled its population expansion, in contrast to P. maackianus. The results revealed that P. maackianus as a canopy-former mainly elongated its shoot length towards the water surface to compensate for the low light conditions, however, it became limited in severe low light stress conditions. V. natans as a rosette adapted to low light stress mainly through photosynthetic adjustments and superior to severely low light than shoot elongation.


Coppens J., Hejzlar, J., Šorf, M., Jeppesen, E., Papastergiadou, E., Stefanidis, K., Erdoğan, Ş., Scharfenberger, U., Mahdy, A., Nõges, P., Tuvikene, A., Baho, D. L., Trigalj, C., Olsen, S. & Beklioğlu, M. (2016) The influence of water level, nutrient loading and climate on nitrogen and phosphorus retention in lakes: a pan-European mesocosm experiment, Hydrobiologia 778, 10-32., http://dx.doi.org/10.1007/s10750-015-2505-9

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The influence of nutrient loading, climate and water depth on nitrogen and phosphorus loss in shallow lakes: a pan-European mesocosm experiment

Losses of phosphorus (P) and nitrogen (N) have important influences on in-lake concentrations and nutrient loading to downstream ecosystems. We performed a series of mesocosm experiments along a latitudinal gradient from Sweden to Greece to investigate the factors influencing N and P loss under different climatic conditions. In six countries, a standardised mesocosm experiment with two water depths and two nutrient levels was conducted concurrently between May and November 2011. Our results showed external nutrient loading to be of key importance for N and P loss in all countries. Almost all dissolved inorganic nitrogen (DIN) and soluble reactive phosphorus (SRP) were lost or taken up in biomass in all mesocosms. We found no consistent effect of temperature on DIN and SRP loss but a significant, though weak, negative effect of temperature on total nitrogen (TN) and total phosphorus (TP) loss in the deeper mesocosms, probably related to higher organic N and P accumulation in the water in the warmer countries. In shallow mesocosms, a positive trend in TN and TP loss with increasing temperature was observed, most likely related to macrophyte growth.


Coppens J., Özen, A., Çakıroğlu, I., Tavşanoğlu, Ü. N., Yozgatlıgil, C., Jeppesen, E. & Beklioğlu, M. (2016) Impact of alternating wet and dry periods on long-term seasonal phosphorus and nitrogen budgets of two shallow Mediterranean lakes, Science of the Total Environment 563–564, 456–467, http://dx.doi.org/10.1016/j.scitotenv.2016.04.028

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Impact of alternating wet and dry periods on long-term seasonal phosphorus and nitrogen budgets of two shallow Mediterranean lakes

The water balance, with large seasonal and annual water level fluctuations, has a critical influence on the nitrogen and phosphorus dynamics of shallow lakes in the semi-arid climate zone. We constructed seasonal water and nutrient budgets for two connected shallow lakes, Lakes Mogan and Eymir, located in Central Anatolia, Turkey. The study period covered 20 years with alternations between dry and wet years as well as restoration efforts including sewage effluent diversion and biomanipulations in Lake Eymir. Both lakes experienced a 1–2 m water level drop during a drought period and a subsequent increase during the wet period, with seasonal water level fluctuations of 0.60 to 0.70 m. During wet years with high water levels, small seasonal differences were observed with a nutrient peak in spring caused by external loading and nutrient loss via retention during summer. During years with low water levels, nutrient concentrations increased due to internal and external loading, exacerbated by evaporative water loss. In Lake Eymir, a shift to eutrophic conditions with turbid water occurred under low water level conditions and consequent internal loading of P from the sediment, causing high nutrient concentrations in summer. Our results indicate a threat of lakes drying out in the semi-arid climate zone if evaporation increases and precipitation decreases as anticipated from the global climate change predictions. In addition, our results show the influence of the water balance on the eutrophication of shallow lakes in the Mediterranean climate zone and highlight the ultimate consequences for lake management.


Cremona, F., Laas, A., Arvola, L., Pierson, D., Nõges, P., Nõges, T. (2016). Numerical exploration of the planktonic to benthic primary production ratios in lakes of the Baltic Sea catchment. Ecosystems 19(8), 1386-1400, http://dx.doi.org/10.1007/s10021-016-0006-y

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Numerical exploration of the planktonic to benthic primary production ratios in lakes of the Baltic Sea catchment

Autotrophic structure refers to the partitioning of whole-ecosystem primary production between benthic and planktonic primary producers. Autotrophic structure remains poorly understood especially because of the paucity of estimates regarding benthic primary production. We used a conceptual model for numerically exploring the autotrophic structure of 13 hemiboreal lakes situated in the Baltic Sea catchment. We also used diel variations in primary production profiles to graphically evaluate levels of light and/or nutrient limitation in lakes. The input morphometric data, light extinction coefficients and dissolved carbon parameters were mostly obtained from in situ measurements. Results revealed that cross- and within-lake autotrophic structure varied greatly: one lake was clearly dominated by benthic production, and three lakes by phytoplankton production. In the rest, phytoplankton production was generally dominant but switch to benthic dominance was possible. The modelled primary production profiles varied according to lake water clarity and bathymetry. Our results clearly indicate that the relative contribution of benthic primary production to whole-lake primary production should be taken into account in studies about hemiboreal and boreal lakes.


Feld, C.K., Segurado, P., Gutiérrez-Cánovas, C. (2016) Analysing the impact of multiple stressors in aquatic biomonitoring data: A 'cookbook' with applications in R, Science of The Total Environment (in press), http://dx.doi.org/10.1016/j.scitotenv.2016.06.243

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Analysing the impact of multiple stressors in aquatic biomonitoring data: A ‘cookbook’ with applications in R

Multiple stressors threaten biodiversity and ecosystem integrity, imposing new challenges to ecosystem management and restoration. Ecosystem managers are required to address and mitigate the impact of multiple stressors, yet the knowledge required to disentangle multiple-stressor effects is still incomplete. Experimental studies have advanced the understanding of single and combined stressor effects, but there is a lack of a robust analytical framework, to address the impact of multiple stressors based on monitoring data. Since 2000, the monitoring of Europe's waters has resulted in a vast amount of biological and environmental (stressor) data of about 120,000 water bodies. For many reasons, this data is rarely exploited in the multiple-stressor context, probably because of its rather heterogeneous nature: stressors vary and are mixed with broad-scale proxies of environmental stress (e.g. land cover), missing values and zero-inflated data limit the application of statistical methods and biological indicators are often aggregated (e.g. taxon richness) and do not respond stressor-specific. Here, we present a ‘cookbook’ to analyse the biological response to multiple stressors using data from biomonitoring schemes. Our ‘cookbook’ includes guidance for the analytical process and the interpretation of results. The ‘cookbook’ is accompanied by scripts, which allow the user to run a stepwise analysis based on his/her own data in R, an open-source language and environment for statistical computing and graphics. Using simulated and real data, we show that the recommended procedure is capable of identifying stressor hierarchy (importance) and interaction in large datasets. We recommend a minimum number of 150 independent observations and a minimum stressor gradient length of 75% (of the most relevant stressor's gradient in nature), to be able to reliably rank the stressor's importance, detect relevant interactions and estimate their standardised effect size. We conclude with a brief discussion of the advantages and limitations of this protocol.


González-Bergonzoni, I., Jeppesen, E., Vidal, N., Teixeira-de Mello, F., Goyenola, G., López-Rodríguez, A., Meerhoff, M. (2016) Potential drivers of seasonal shifts in fish omnivory in a subtropical stream, Hydrobiologia 768, 183-196, http://dx.doi.org/10.1007/s10750-015-2546-0

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Potential drivers of seasonal shifts in fish omnivory in a subtropical stream

The trophic structure of fish assemblages often varies seasonally, following the changes in food availability and supposedly water temperature. To unveil potential drivers of trophic shifts, we studied changes in fish trophic structure at both whole-assemblage and species levels at contrasting food availability and water temperatures in a subtropical stream. We analysed the diet of the most abundant omnivorous species (Bryconamericus iheringii) monthly along the year, searching for relationships with environmental variables changing seasonally (i.e. temperature and water level) and with fish reproductive stage. We ran a single-species food choice field experiment with fixed animal and vegetal food availability in contrasting seasons to test food availability as driver of diet shifts. At the assemblage level, we found a higher consumption of vegetal during summer, reflecting the increased proportion of vegetal in the diet of omnivores, which dominated the assemblage. At the species level, the enhanced vegetal consumption was related to increases in temperature and reduction in water level. Moreover, fish selected for vegetal during summer and for animal food in winter under experimental conditions. Our findings support the role of temperature driving food web dynamics by increasing fish herbivory towards warmer scenarios, with potential strong implications for whole-assemblage trophic structure.


Grizzetti, B., Lanzanova, D., Liquete, C., Reynaud, A. & A.C. Cardoso (2016) Assessing water ecosystem services for water resource management, Environmental Science & Policy, 61, 194-203, http://dx.doi.org/10.1016/j.envsci.2016.04.008

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Assessing water ecosystem services for water resource management

Ecosystem service concepts can offer a valuable approach for linking human and nature, and arguments for the conservation and restoration of natural ecosystems. Despite an increasing interest in the topic, the application of these concepts for water resource management has been hampered by the lack of practical definitions and methodologies. In this study we review and analyse the current literature and propose an approach for assessing and valuing ecosystem services in the context of water management. In particular, to study the link between multiple pressures, ecological status and delivery of ecosystem services in aquatic ecosystems under different scenarios of measures or future changes. This is of interest for the development of River Basin Management Plans under the EU Water Framework Directive. We provide a list of proxies/indicators of natural capacity, actual flow and social benefit for the biophysical assessment of the ecosystem services. We advocate the use of indicators of sustainability, combining information on capacity and flow of services. We also suggest methods for economic valuation of aquatic ecosystem for each service and spatial scale of application. We argue that biophysical assessment and economic valuation should be conducted jointly to account for the different values of ecosystem services (ecologic, social and economic) and to strengthen the recognition of human dependency on nature. The proposed approach can be used for assessing the benefits of conservation and restoration of aquatic ecosystems in the implementation of the EU water policy.


Gu, J., Jin, H, He, H., Ning, X., Yu, J., Tan, B., Jeppesen, E. & Li, K. (2016) Effects of small-sized crucian carp Carassius auratus on the growth of submerged macrophytes: implications for shallow lake restoration, Ecoligal Engineering 95, 567-573, http://dx.doi.org/10.1016/j.ecoleng.2016.06.118

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Effects of small-sized crucian carp (Carassius carassius) on the growth of submerged macrophytes: Implications for shallow lake restoration

Reestablishment of submerged macrophytes is considered important when restoring shallow eutrophic lakes. To improve water clarity and consequently the growth conditions of macrophytes, removal of plankti-benthivorous fish has been used. In subtropical shallow lakes, however, rapid recruitment of small fish, especially benthivores during restoration, may hamper early reestablishment of submerged macrophytes. Crucian carp (Carassius carassius) and Vallisneria natans are common species dominated in subtropical shallow lakes. To investigate the effect of small benthivorous fish on the growth of Vallisneria natans, a 28-day outdoor controlled experiment was undertaken in 12 mesocosms with three densities of Carassius carassius − low (10 g m −2), high (40 g m −2) and no fish (all in four replicates). The results showed that the fish significantly increased chlorophyll-a concentrations and periphyton biomass in both fish treatments, most significantly at high density for Chl a. This concurs with an increase in nutrient concentrations , likely mediated by fish sediment disturbance and excretion, and a reduction of zooplankton biomass (less algal grazing). Increased concentrations of inorganic suspended solids with increasing fish density further enhanced turbidity, causing shading of the macrophytes. Accordingly, the relative growth rate, ramet number and root/leaf ratio of V. natans decreased significantly at low and high fish density compared with the controls, but the effects did not depend on fish density. However, mean leaf length rose with increasing fish density, likely to allow the plants to obtain more light. Overall, our results show that not only large-bodied carp, as demonstrated frequently, but also small-sized crucian carp posed a constraint on submerged macrophyte reestablishment, and we conclude that crucian carp may hamper restoration efforts in subtropical shallow lakes. Restoration by biomanipulation should therefore target also small-sized crucian carp.


Gu, J., Xu, Z., Ning, X., Jin, H., He, H., Yu, J., Jeppesen E., Li, K. (2016). Response of eelgrass (Vallisneria natans) to increasing nitrogen loading is depending on sediment nutrient characteristics. Water 8, 563, http://dx.doi.org/10.3390/w8120563

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Response of eelgrass (Vallisneria natans) to increasing nitrogen loading is depending on sediment nutrient characteristics

High nitrogen (N) loading may contribute to recession of submerged macrophytes in shallow lakes; yet, its influences vary depending on environmental conditions. In August 2013, we conducted a 28-day factorial-designed field mesocosm experiment in Lake Taihu at the Taihu Laboratory for Lake Ecosystem Research (TLLER) to examine the effects of high N loading on the growth of Vallisneria natans in systems with contrasting sediment types. We ran the experiments with two levels of nutrient loading—present-day external nutrient loading (average P: 5 µg·L −1 ·day −1 , N: 130 µg·L −1 ·day −1) and P: 5 µg·L −1 ·day −1 , and with three times higher N loading (N: 390 µg·L −1 ·day −1) and used sediment with two contrasting nutrient levels. V. natans growth decreased significantly with increasing N loading, the effect being dependent, however, on the nutrient status of the sediment. In low nutrient sediment, relative growth rates, leaf biomass and root biomass decreased by 11.9%, 18.2% and 23.3%, respectively, at high rather than low N loading, while the decline was larger (44.0%, 32.7% and 41.8%, respectively) when using high nutrient sediment. The larger effect in the nutrient-rich sediment may reflect an observed higher shading of phytoplankton and excess nutrient accumulation in plant tissue, though potential toxic effects of the high-nutrient sediment may also have contributed. Our study confirms the occurrence of a negative effect of increasing N loading on submerged plant growth in shallow nutrient-enriched lakes and further shows that this effect is augmented when the plants grow in nutrient-rich sediment. External N control may, therefore, help to protect or restore submerged macrophytes, especially when the sediment is enriched with nutrients and organic matter.


Gutierrez, M.F., Devercelli, M., Brucet, S., Lauridsen, T. L., Søndergaard M. & Jeppesen, E. (2016) Is recovery of large-bodied zooplankton after nutrient loading reduction hampered by climate warming? A long-term study of shallow hypertrophic Lake Søbygaard, Denmark, Water 8 (online), http://dx.doi.org/10.3390/w8080341

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Nutrient Loading Reduction Hampered by Climate Warming? A Long-Term Study of Shallow Hypertrophic Lake Søbygaard, Denmark

Nutrient fluctuations and climate warming can synergistically affect trophic dynamics in lakes, resulting in enhanced symptoms of eutrophication, thereby potentially counteracting restoration measures. We performed a long-term study (23 years) of zooplankton in Danish Lake Søbygaard, which is in recovery after nutrient loading reduction, but now faces the effects of climate warming. We hypothesized that the recovery of large-bodied zooplankton after nutrient loading reduction would be hampered by climate warming through indirect effects on fish size structure. We found a shift in macrozooplankton from initial dominance of Daphnia spp. towards Bosmina spp. as well as a decline in the body size of copepods and an increase in the abundance of nauplii. These changes coincided with the increase in small sized fish as a result of rising water temperature. Despite a reduction in body size, the total biomass of cladocerans increased coinciding with a diminished fish catch per unit effort (CPUE), and likely then an overall reduction in the predation on zooplankton. A cascading effect to phytoplankton was evidenced by enhanced zooplankton:phytoplankton and cladoceran:phytoplankton ratios and a decrease in Chl-a:TP and Chl-a:TN ratios. Our results indicate that climate warming, through changes in the size structure of fish community, has major effects on zooplankton size structure. In Lake Søbygaard, the decline in zooplankton size did not prevent, but modulated, the positive cascading effect on phytoplankton through an expected diminished fish CPUE related to nutrient loading reduction.


Haande, S., Moe, S. J., Couture, R. M., (2016). Phytoplankton and other monitoring data from Lake Vansjø. Freshwater Metadata Journal 15, 1-8, http://dx.doi.org/10.15504/fmj.2016.15

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Phytoplankton and other monitoring data from Lake Vansjø

This report gives an overview of biological and other environmental monitoring data from Lake Vansjø in the Morsa river basin district, South-East Norway. The lake is impacted by eutrophication and has been subject to several nutrient abatement measures. The dataset comprises phytoplankon data at species level from 2005-2015, and water chemistry data from the period 1980-2015. The dataset is available online from NIVA's web portal AquaMonitor and will be updated regularly with new monitoring data.


Hu, F., Bolding, K., Bruggeman, J., Jeppesen, E., Flindt, M. R., Mooij, W, M., Janse, J., Janssen, A., van Gerven, L. & Trolle, D. (2016) FABM-PCLake – linking aquatic ecology with hydrodynamics, Geoscientific Model Development 9, 2271-2278, http://dx.doi.org/ 10.5194/gmd-9-2271-2016

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FABM-PCLake – linking aquatic ecology with hydrodynamics

This study presents FABM-PCLake, a complete redesign of the PCLake aquatic ecosystem model, which we implemented into the Framework for Aquatic Biogeochemical Models (FABM). In contrast to the original model, which was designed for temperate, fully mixed freshwater lakes, the new FABM-PCLake represents an integrated aquatic ecosystem model that enables simulations of hydrodynamics and biogeochemical processes for zero dimensional, one-dimensional as well as three-dimensional heterogeneous environments. FABM-PCLake describes interactions between multiple trophic levels, including piscivorous, zooplanktivorous and benthivorous fish, zooplankton, zoobenthos, three groups of phytoplankton and rooted macrophytes. The model also accounts for oxygen dynamics and nutrient cycling for nitrogen, phosphorus and silicon, both within the pelagic and benthic domains. FABM-PCLake includes a two-way communication between the biogeochemical processes and the physics, where some biogeochemical state variables (e.g., phytoplankton) influence light attenuation and thereby the spatial and temporal distributions of light and heat. At the same time, the physical environment, including water currents, light and temperature influence a wide range of biogeochemical processes. The model enables studies on ecosystem dynamics in physically heterogeneous environments (e.g., stratifying water bodies, and water bodies with horizontal gradient in physical and biogeochemical properties), and through FABM also enables data assimilation and multi-model ensemble simulations. Examples of relevant model applications include climate change impact studies and environmental impact assessment scenarios for lakes and reservoirs worldwide.


Hu, E., He, H., Su, Y., Jeppesen, E., Liu, Z. (2016). The uses of multi-carbon sources by zooplankton in an oligotrophic lake from Tibetan Plateau. Water 8, 565, http://dx.doi.org/10.3390/w8120565

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The uses of multi-carbon sources by zooplankton in an oligotrophic lake from Tibetan Plateau

We applied natural abundance stable isotope δ 13 C and radiocarbon ∆ 14 C analyses to investigate trophic linkages between zooplankton and their potential food sources (phytoplankton, submersed plants, and allochthonous organic carbon) in Lake Nam Co, one of the largest oligosaline and oligotrophic lakes in the Tibetan Plateau, in southwest China. The δ 13 C and ∆ 14 C levels of the calanoid copepod Arctodiaptomus altissimus pectinatus indicate that it uses different carbon sources. Thus, based on a two-isotope mixing model, our results suggested that recently synthesized but 14 C-depleted primary producers (phytoplankton and submersed plants) were the most important sources of carbon, together contributing 92.2% of the zooplankton biomass. Allochthonous organic carbon and dissolved organic carbon constituted 4.7% and 3.1% of the carbon in the diet of zooplankton, respectively. Our findings from Lake Nam Co suggest that the carbon in the food webs of lakes located in a glaciated environment originates from various sources of different ages.


Idrizaj, A., Laas, A., Anijalg, U., Nõges, P. (2016). Horizontal differences in ecosystem metabolism of a large shallow lake. Journal of Hydrology 535, 93–100, http://dx.doi.org/10.1016/j.jhydrol.2016.01.037

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Horizontal differences in ecosystem metabolism of a large shallow lake

The causes of horizontal differences in metabolic activities between lake zones are still poorly understood. We carried out a two-year study of lake metabolism in two contrasting parts of a large shallow lake using the open-water technique based on high-frequency measurements of dissolved oxygen concentrations. We expected that the more sheltered and macrophyte-rich southern part of the lake receiving a high hydraulic load from the main inflow will exhibit equal or higher rate of metabolic processes compared to the open pelagic zone, and higher temporal variability, including anomalous metabolic estimates such as negative gross primary production (GPP) or community respiration (CR) due to rapid water exchange. Our results showed that anomalous metabolic estimates occurred at both stations with a similar frequency and were related rather to certain wind directions, which likely contributed to stronger water exchange between the littoral and pelagic zones. Periods of auto- and heterotrophy (daily mean NEP> or <0) had a 50:50 distribution at the Central Station while the proportions were 30:70 at the Southern Station. High areal GPP estimated in our study exceeding nearly twice the long-term average 14C primary production, showed the advantages of the free-water technique in integrating the metabolism of all communities, a large part of which has remained undetected by the traditional bottle or chamber incubation techniques.


Iglesias, C., Meerhoff, M., Johanson, L. S., Gonzalez-Bergonzoni, I., Mazzeo, N., Pacheco, J. P., Teixeira de Mello, F., Goyenola, G., Lauridsen, T., Sondergard, M. Davidson, T. & Jeppesen, E. (2016) Stable isotopes analysis confirms substantial differences between subtropical and temperate shallow lakes food webs, Hydrobiologia (online), http://dx.doi.org/10.1007/s10750-016-2861-0

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Stable isotope analysis confirms substantial differences between subtropical and temperate shallow lake food webs

Differences in trophic web structure in otherwise similar ecosystems as a consequence of direct or indirect effects of ambient temperature differences can lead to changes in ecosystem functioning. Based on nitrogen and carbon stable isotope analysis, we compared the food-web structure in a series of subtropical (Uruguay, 30–35°S) and temperate (Denmark, 55–57°N) shallow lakes. The food-web length was on average one trophic position shorter in the subtropical shallow lakes compared with their temperate counterparts. This may reflect the fact that the large majority of subtropical fish species are omnivores (i.e., feed on more than one trophic level) and have a strong degree of feeding niche overlap. The shapes of the food webs of the subtropical lakes (truncated and trapezoidal) suggest that they are fuelled by a combination of different energy pathways. In contrast, temperate lake food webs tended to be more triangular, likely as a result of more simple pathways with a top predator integrating different carbon sources. The effects of such differences on ecosystem functioning and stability, and the connection with ambient temperature as a major underlying factor, are, however, still incipiently known.


Jeppesen, E., Trolle, D., Davidson, T. A., Bjerring, R., Søndergaard, M., Johansson, L. S.& Lauridsen, T. L. (2016) Major changes in CO2 efflux when shallow lakes shift from turbid to a clear water state, Hydrobiologia 778, 33-44, http://dx.doi.org/10.1007/s10750-015-2469-9

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Major changes in CO2 efflux when shallow lakes shift from a turbid to a clear water state

Lakes can be sources or sinks of carbon, depending on local conditions. Recent studies have shown that the CO2 efflux increases when lakes recover from eutrophication, mainly as a result of a reduction in phytoplankton biomass, leading to less uptake of CO2 by producers. We hypothesised that lake restoration by removal of coarse fish (biomanipulation) or invasion of mussels would have a similar effect. We studied 14–22 year time series of five temperate Danish lakes and found profound effects on the calculated CO2 efflux of major shifts in ecosystem structure. In two lakes, where limited colonisation of submerged macrophytes occurred after biomanipulation or invasion of zebra mussels (Dreissena polymorpha), the efflux increased significantly with decreasing phytoplankton chlorophyll a. In three lakes with major interannual variation in macrophyte abundance, the efflux declined with increasing macrophyte abundance in two of the lakes, while no relation to macrophytes or chlorophyll a was found in the third lake, likely due to high groundwater input to this lake. We conclude that clearing water through invasive mussels or lake restoration by biomanipulation may increase the CO2 efflux from lakes. However, if submerged macrophytes establish and form dense beds, the CO2 efflux may decline again.


Jo, H., Ventura, M., Vidal, N., Gim J.-S., Buchaca, T., Barmuta, L. A., Jeppesen, E. & Joo, G.-J. (2016) Discovering hidden biodiversity: the use of complementary monitoring of fish diet based on DNA barcoding in freshwater ecosystems, Ecology and Evolution 6, 219–232, http://dx.doi.org/10.1002/ece3.1825

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Discovering hidden biodiversity: The use of complementary monitoring of fish diet based on DNA barcoding in freshwater ecosystems

Ecological monitoring contributes to the understanding of complex ecosystem functions. The diets of fish reflect the surrounding environment and habitatsand may, therefore, act as useful integrating indicators of environmental status. It is, however, often difficult to visually identify items in gut contents to species level due to digestion of soft-bodied prey beyond visual recognition, but new tools rendering this possible are now becoming available. We used a molecular approach to determine the species identities of consumed diet items of an introduced generalist feeder, brown trout (Salmo trutta), in 10 Tasmanian lakes and compared the results with those obtained from visual quantification of stomach contents. We obtained 44 unique taxa (OTUs) belonging to five phyla, including seven classes, using the barcode of life approach from cytochrome oxidase I (COI). Compared with visual quantification, DNA analysis showed greater accuracy, yielding a 1.4-fold higher number of OTUs. Rarefaction curve analysis showed saturation of visually inspected taxa, while the curves from the DNA barcode did not saturate. The OTUs with the highest proportions of haplotypes were the families of terrestrial insects Formicidae, Chrysomelidae, and Torbidae and the freshwater Chironomidae. Haplotype occurrence per lake was negatively correlated with lake depth and transparency. Nearly all haplotypes were only found in one fish gut from a single lake. Our results indicate that DNA barcoding of fish diets is a useful and complementary method for discovering hidden biodiversity.


Jovanovic, B., Bezirci, G., Cagan, A. S., Coppens, J., Levi, E. E., Oluz, Z., Tuncel, E., Duran, H., Beklioglu, M. (2016). Food web effects of titanium dioxide nanoparticles in an outdoor freshwater mesocosm experiment. Nanotoxicology 10(7), 902-912, http://dx.doi.org/10.3109/17435390.2016.1140242

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Food web effects of titanium dioxide nanoparticles in an outdoor freshwater mesocosm experiment

Over the course of 78 days, 9 outdoor mesocosms, each with 1350 L capacity, were situated on a pontoon platform in the middle of a lake and exposed to 0 µg L−1 TiO2, 25 µg L−1 TiO2, or 250 µg L−1 TiO2 nanoparticles in the form of E171 TiO2 human food additive five times a week. Mesocosms were inoculated with sediment, phytoplankton, zooplankton, macroinvertebrates, macrophytes, and fish before exposure, ensuring a complete food web. Physicochemical parameters of the water, nutrient concentrations, and biomass of the taxa were monitored. Concentrations of 25 µg L−1 TiO2 and 250 µg L−1 TiO2 caused a reduction in available soluble reactive phosphorus in the mesocosms by 15% and 23%, respectively, but not in the amount of total phosphorous. The biomass of Rotifera was significantly reduced by 32% and 57% in the TiO2 25 µg L−1 and TiO2 250 µg L−1 treatments, respectively, when compared to the control; however, the biomass of the other monitored groups—Cladocera, Copepoda, phytoplankton, macrophytes, chironomids, and fish—remained unaffected. In conclusion, environmentally relevant concentrations of TiO2 nanoparticles may negatively affect certain parameters and taxa of the freshwater lentic aquatic ecosystem. However, these negative effects are not significant enough to affect the overall function of the ecosystem, as there were no cascade effects leading to a major change in its trophic state or primary production.


Kangur, K., Ginter, K., Kangur, P., Kangur, A., Nõges, P., Laas, A. (2016). Changes in water temperature and chemistry preceding a massive kill of bottom-dwelling fish: An analysis of high–frequency buoy data of shallow Lake Võrtsjärv (Estonia). Inland Waters 6(4), 535-542, http://dx.doi.org/10.5268/IW-6.4.869

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Changes in water temperature and chemistry preceding a massive kill of bottom-dwelling fish: An analysis of high–frequency buoy data of shallow Lake Võrtsjärv (Estonia)

Although massive fish kills are wide-spread and can be economically devastating, there is little information on exact causal mechanisms of fish kills in nature. In large shallow Lake Vortsjarv, sporadic fish kills have been registered mainly in cold winters, yet in 2013, an unexpected fish kill occurred beginning mid-June. At the time of the fish kill, an investigation was conducted to determine species composition, number, and sizes of dead fish along the lake shore. To determine possible causes of the fish kill, we analysed the dynamics of key physical and chemical parameters of lake water, including diurnal fluctuations of water temperature (WT), pH, dissolved oxygen (DO), ammonium ion concentrations (NH4-N), and the development of water stratification, during the growing season of 2013 using high-frequency water quality monitoring buoy and monthly manual monitoring data. Environmental data between 2010 and 2012 were used as a reference because no fish kill occurred. The results suggest that the fish kill was induced by a combination of successive and co-occurring extreme water parameters such as high WT (up to 24.5 °C), pH (up to 9.2), and NH4-N (up to 0.13 mg L⁻¹), short-term stratification, and low DO concentration in the bottom water (0.49 mg L-1, saturation 5.4%) induced by quick warming of this shallow lake after a long ice-covered period and leading to a likely ammonia poisoning and hypoxia. The main target species was the bottom-dwelling ruffe (Gymnocephalus cernuus), indicating that the summer kill started at the bottom of the lake. The event highlights the significance of short-term disturbances on fish populations, which can be detected only using high-frequency monitoring data.


Kristensen, P. B., Riis, T., Dylmer, H.E., Kristensen, E. A., Meerhoff, M., Olesen, B., Teixeira-de Mello, F., Baattrup-Pedersen, A., Cavalli, G. & Jeppesen, E. (2016) Baseline identification in stable isotope studies of temperate lotic systems and implications for calculated trophic positions, Freshwater Science 35, 909-921, http://dx.doi.org/10.1086/687284

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Baseline identification in stable-isotope studiesof temperate lotic systems and implications for calculated trophic positions

Stable-isotope analysis is widely used in aquatic ecosystem studies to evaluate trophic structure and resource dynamics. Because δ15N values vary in freshwater systems, e.g., reflecting variations in land use, suitable baseline indicators must be specified. Few investigators have identified specific baseline organisms based on thorough and methodical screening. We screened for baseline organisms in temperate lotic waters based on 4 criteria: 1) baseline organisms should be easy to collect, 2) within-site variation in δ15N levels should be low, 3) δ15N should reflect land use, and 4) trophic position (TP) of consumers calculated from the baseline should be independent of system-specific δ15N variability as long as no systematic change in food consumption occurred. We investigated individual taxa and bulked groups representing different feeding modes as baselines. We found that Simuliidae, a sestonic filter feeder, fulfilled all criteria. Furthermore, TP estimates of 2 common fishes that were based on the Simuliidae or grouped filterers as baselines were the only estimates in our study that were independent of landuse changes. In addition, the diet of these fishes did not change across land use as based on stable-isotope mixing-model analysis. Simuliidae also had the lowest within-site variation, i.e., the lowest trophic level range, probably a result of uniform feeding behavior. Therefore, Simuliidae and grouped filterers could be suitable baseline indicators in future studies. We recommend minimizing δ15N variability in and among systems because the precise, complex choice, timing, or proportions of food sources consumed cannot be mimicked. We also promote combining TP estimation and mixing-model analyses as a strong tool in studies of stream food webs.


Kuha, J., Arvola, L., Hanson, P.C., Huotari, J., Huttula, T., Juntunen, J., Järvinen, M., Kallio, K., Ketola, M., Kuoppamäki, K., Lepistö, A., Lohila, A., Paavola, R., Vuorenmaa, J., Winslow, L., Karjalainen, J. (2016). Response of boreal lakes to episodic weather events. Inland Waters 6, 523-534, http://dx.doi.org/10.5268/IW-6.4.886

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Response of boreal lakes to episodic weather events

Weather-induced episodic mixing events in lake ecosystems are often unpredictable, and their impacts are therefore poorly known. The impacts can be short-lived, including changes in water temperature and stratification, but long-lasting effects on the lake’s biology may also occur. In this study we used automated water quality monitoring (AWQM) data from 8 boreal lakes to examine how the episodic weather-induced mixing events influenced thermal structure, hypolimnetic dissolved oxygen (DO), fluorometric chlorophyll estimates (Chl-a), and lake metabolism and how these events varied in frequency and magnitude in lakes with different characteristics. Rise in wind speed alone had an effect on the lakes with the weakest thermal stability, but a decrease in air temperature together with strong wind induced mixing events in all lakes. The return period of these mixing events varied widely (from 20 to 92 d) and was dependent on the magnitude of change in weather. In lakes with strong stability, thermal structure and hypolimnetic DO concentration were only slightly affected. Weather-induced mixing in the upper water column diluted the surface water Chl-a repeatedly, whereas seasonal maximum occurred in late summer on each lake. Although Finnish lakes have been characterized with stable stratification during summer, we observed many substantial mixing events of relatively short return periods relevant to both chemical and biological properties of the lakes.


Laas, A., Cremona, F., Meinson, P., Rõõm, E.-I., Nõges, T., Nõges, P. (2016). Summer depth distribution profiles of dissolved CO2 and O2 in shallow temperate lakes reveal trophic state and lake type specific differences. Science of the Total Environment 566–567, 63–75, http://dx.doi.org/10.1016/j.scitotenv.2016.05.038

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Summer depth distribution profiles of dissolved CO2 and O2 in shallow temperate lakes reveal trophic state and lake type specific differences

Knowledge about dissolved oxygen (DO) and carbon dioxide (CO2) distribution in lakes has increased considerably over the last decades. However, studies about high resolution dynamics of dissolved CO2 in different types of lakes over daily or weekly time scales are still very scarce. We measured summertime vertical DO and CO2 profiles at sub-hourly intervals during one week in eight Estonian lakes representing different lake types according to European Water Framework Directive. The lakes showed considerable differences in thermal stratification and vertical distribution of dissolved oxygen and CO2 as well as different diurnal dynamics over the measurement period. We observed a continuous CO2 supersaturation in the upper mixed layer of the alkalitrophic (calcareous groundwater-fed) lake and the dark soft-water lake showing them as CO2 emitting "chimneys" although with different underlying mechanisms. In three lake types strong undersaturation with CO2 occurred in the surface layer characterising them as CO2 sinks for the measurement period while in another three types the surface layer CO2 was mostly in equilibrium with the atmosphere. Factor analysis showed that DO% in the surface layer and the strength of its relationship with CO2% were positively related to alkalinity and negatively to trophic state and DOC gradients, whereas deeper lakes were characterised by higher surface concentration but smaller spatial and temporal variability of CO2. Multiple regression analysis revealed lake area, maximum depth and the light attenuation coefficient as variables affecting the largest number of gas regime indicators. We conclude that the trophic status of lakes in combination with type specific features such as morphometry, alkalinity and colour (DOC) determines the distribution and dynamics of dissolved CO2 and DO, which therefore may indicate functional differences in carbon cycling among lakes.


Levi, E. E., Bezirci, G., Çakıroğlu, A. İ., Turner, S., Bennion, H., Kernan, M., Jeppesen, E. & Beklioğlu, M. (2016) Multi-proxy palaeoecological responses to water-level fluctuations in three shallow Turkish lakes, Palaeogeography, Palaeoclimatology, Palaeoecology 449, 553-566, http://dx.doi.org/10.1016/j.palaeo.2016.02.052

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Multi-proxy palaeoecological responses to water-level fluctuations in three shallow Turkish lakes

Natural or human-induced water-level fluctuations influence the structure and function of shallow lakes, especially in semi-arid to arid climate regions. In order to reliably interpret the effect of water-level changes from sedimentary remains in the absence of historical data, it is crucial to understand the variation in sedimentary proxies in relation to water level measurements. Here, we took advantage of existing water surface elevation data on three large shallow lakes in Turkey to elucidate the impact of lake-level changes on benthic-pelagic primary production over the last 50–100 years. Sub-fossil cladocerans, diatoms, plant remains and pigments were investigated as biological variables; X-ray fluorescence (XRF) and loss on ignition (LOI) analyses were conducted as geochemical-physical variables on a set of 210Pb and 137Cs dated cores. Dating of the cores were robust, with the exception of uncertainties in Lake Marmara littoral core due to low unsupported 210Pb activities and high counting errors. Results indicated that Lake Marmara was dominated by benthic species throughout the sediment record, while Lakes Beyşehir and Uluabat shifted from a littoral-dominated system to one with increased pelagic species abundance. In all cores there was a stronger response to longer-term (decadal) and pronounced water-level changes than to short-term (annual-biennial) and subtle changes. It was also noted that degree of alteration in proxies differed between lakes, through time and among pelagic-littoral areas, likely emphasising differences in depositional environments and/or resolution of sampling and effects of other stressors such as eutrophication. Our results highlight lake-specific changes associated with water-level fluctuations, difficulties of conducting studies at required resolution in lakes with rather mixed sediment records and complexity of palaeolimnological studies covering recent periods where multiple drivers are in force. They further emphasise the need to include instrumental records when interpreting effects of recent water-level changes from sediment core data in large shallow lakes.


Levi, P. S., Starnawski, P., Poulsen, B., Baattrup-Pedersen, A., Schramm, A., Riis, T. (2016). Microbial diversity varies with habitat complexity and biofilm function in macrophyte-rich streams. Oikos, Synthesising Ecology 126(3), 398-409, http://dx.doi.org/10.1111/oik.03400

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Microbial diversity varies with habitat complexity and biofilm function in macrophyte-rich streams

Biofilms in streams play an integral role in ecosystem processes and function yet few studies have investigated the broad diversity of these complex prokaryotic and eukaryotic microbial communities. Physical habitat characteristics can affect the composition and abundance of microorganisms in these biofilms by creating microhabitats. Here we describe the prokaryotic and eukaryotic microbial diversity of biofilms in sand and macrophyte habitats (i.e. epipsammon and epiphyton, respectively) in five macrophyte-rich streams in Jutland, Denmark. The macrophyte species varied in growth morphology, C:N stoichiometry, and preferred stream habitat, providing a range in environmental conditions for the epiphyton. Among all habitats and streams, the prokaryotic communities were dominated by common phyla, including Alphaproteobacteria, Bacteriodetes, and Gammaproteobacteria, while the eukaryotic communities were dominated by Stramenopiles (i.e. diatoms). For both the prokaryotes and eukaryotes, the epipsammon were consistently the most diverse communities and the epiphytic communities were generally similar among the four macrophyte species. However, the communities on the least complex macrophyte, Sparganium emersum, had the lowest richness and evenness and fewest unique OTUs, whereas the macrophyte with the most morphological complexity, Callitriche spp., had the highest number of unique OTUs. In general, the microbial taxa were ubiquitously distributed across the relatively homogeneous Danish landscape as determined by measuring the similarity among communities (i.e. Sørensen similarity index). Furthermore, we found significant correlations between microbial diversity (i.e. Chao1 rarefied richness and Pielou's evenness) and biofilm structure and function (i.e. C:N ratio and ammonium uptake efficiency, respectively); communities with higher richness and evenness had higher C:N ratios and lower uptake efficiency. In addition to describing the prokaryotic and eukaryotic community composition in stream biofilms, our study indicates that 1) physical habitat characteristics influence microbial diversity and 2) the variation in microbial diversity may dictate the structural and functional characteristics of stream biofilm communities.


Liquete, C., Cid, N., Lanzanova, D., Grizzetti, B., Reynaud, A. (2016). Perspectives on the link between ecosystem services and biodiversity: The assessment of the nursery function. Ecological Indicators 63, 249-257, http://dx.doi.org/10.1016/j.ecolind.2015.11.058

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Perspectives on the link between ecosystem services and biodiversity: The assessment of the nursery function

The relationship between biodiversity and each ecosystem service or bundle of ecosystem services (e.g. win−win, win−lose or win−neutral) is an active field of research that requires structured and consistent information. The application of that research for conservation and decision-making can be hampered by the ambiguity found in the definition of the nursery function under the ecosystem service perspective. In this paper, we review how the role of nursery habitats is included in the ecosystem services literature, covering conceptual, biophysical and economic reflections. The role of ecosystems as nurseries is mostly analyzed in coastal environments. The main observation is that there is no consensus on the consideration of the nursery function as a service (e.g. which species or habitats) or on how to assess it (e.g. which indicators or valuation methods). After that review, we analyze three different interpretations given to the nursery function, namely the ecological, conservationist and economic point of view; and we distinguish between different types of assessment that may consider the nursery function. We conclude that the nursery function can be considered an ecosystem service on its own right when it is linked to a concrete human benefit and not when it is represented with indicators of general biodiversity or ecosystem condition. Thus, the analysis of the delivery of ecosystem services should be differentiated from the analysis of ecological integrity. Only with this distinction science may be able to quantify the link between biodiversity and ecosystem services and policy may be effective in halting biodiversity loss. Similar considerations could apply for other biodiversity constituents that may be treated as ecosystem services.


Lorenz, S., Leszinski, M., Graeber, D. (2016). Meander reconnection method determines restoration success for macroinvertebrate communities in a German lowland river. International Review of Hydrobiology 101, 123-131, http://dx.doi.org/10.1002/iroh.201501823

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Meander reconnection method determines restoration success for macroinvertebrate communities in a German lowland river

Re-meandering of degraded rivers is a frequently implemented measure in river restoration. A simple solution is reconnection of old meanders; however, its success likely depends on the reconnection method. We conducted a field study to analyze the benefits of a fullyreconnected (fully opened meander, blocked main channel) and a partially reconnected meander (opened downstream, pipe bypass from main channel upstream, still open main channel) for macroinvertebrate communities in a German lowland river. Immediately upon reconnection of the two meanders, habitat diversity, and macroinvertebrates were recorded for three years with sampling in spring and in summer each year. The results of a principal response curve analysis show that the macroinvertebrate community in the fully reconnected meander reflected main channel reference conditions after 1.5 years. The macroinvertebrate community composition was not improved relative to in-stream reference conditions within the partially reconnected meander, which could be attributed to the almost complete lack of flow changes that resulted in missing improvements of substrate diversity. Our results show that the meander reconnection method must sufficiently affect the basic hydromorphological requirements to achieve reference macroinvertebrate community composition. Measures including hydromorphological conditions are therefore recommended for employment in environmental management.


Malve, O., Hjerppe, T., Tattari, S., Vaisanen, S., Huttunen, I., Kotamaki, N., Kallio, K., Taskinen, A., Kauppila, P. (2016). Participatory operations model for cost-efficient monitoring and modeling of river basins – A systematic approach. Science of the Total Environment 540, 79-89, http://dx.doi.org/10.1016/j.scitotenv.2015.06.105

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Participatory operations model for cost-efficient monitoring and modeling of river basins – A systematic approach

The worldwide economic downturn and the climate change in the beginning of 21st century have stressed the need for cost efficient and systematic operations model for the monitoring and management of surface waters. However, these processes are still all too fragmented and incapable to respond these challenges. For example in Finland, the estimation of the costs and benefits of planned management measures is insufficient. On this account, we present a new operations model to streamline these processes and to ensure the lucid decision making and the coherent implementation which facilitate the participation of public and all the involved stakeholders. The model was demonstrated in the real world management of a lake. The benefits, pitfalls and development needs were identified. After the demonstration, the operations model was put into operation and has been actively used in several other management projects throughout Finland.


Meinson, P., Idrizaj, A., Nõges, P., Nõges, T., Laas, A. (2016). Continuous and high-frequency measurements in limnology: History, applications and future challenges. Environmental Reviews 24(1), 52-62, http://dx.doi.org/10.1139/er-2015-0030

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Continuous and high-frequency measurements in limnology: History, applications and future challenges

Over the past 15 years, an increasing number of studies in limnology have been using data from high-frequency measurements (HFM).This new technology offers scientists a chance to investigate lakes at time scales that were not possible earlier and in places where regular sampling would be complicated or even dangerous. This has allowed capturing the effects of episodic or extreme events, such as typhoons on lakes. In the present paper we review the various fields of limnology such as monitoring, studying highly dynamic processes, lake metabolism studies, and budget calculations where HFM has been applied, and which have benefitted most from the application. Our meta-analysis showed that more than half of the high-frequency studies from lakes were made in North-America and Europe. The main field of application has been lake ecology (monitoring, lake metabolism) followed by physical limnology. Water temperature and dissolved oxygen have been the most universal and commonly measured parameters and we review the various study purposes for which these measurements have been used. Although a considerable challenge forthe future, our review highlights that broadening the spatial scale of HFM would substantially broaden the applicability of these data across a spectrum of different fields.


Moe, S. J., Haande, S., Couture, R. M. (2016). Climate change, cyanobacteria and ecological status of lakes: A Bayesian network approach. Ecological Modelling 337, 330-347, http://dx.doi.org/10.1016/j.ecolmodel.2016.07.004

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Climate change, cyanobacteria and ecological status of lakes: A Bayesian network approach

Eutrophication of lakes and the risk of harmful cyanobacterial blooms due is a major challenge for management of aquatic ecosystems, and climate change is expected to reinforce these problems. Modelling of aquatic ecosystems has been widely used to predict effects of altered land use and climate change on water quality, assessed by chemistry and phytoplankton biomass. However, the European Water Framework Directive requires more advanced biological indicators for the assessment of ecological status of water bodies, such as the amount of cyanobacteria. We applied a Bayesian network (BN) modelling approach to link future scenarios of climate change and land-use management to ecological status, incorporating cyanobacteria biomass as one of the indicators. The case study is Lake Vansjø in Norway, which has a history of eutrophication and cyanobacterial blooms. The objective was (i) to assess the combined effect of changes in land use and climate on the ecological status of a lake and (ii) to assess the suitability of the BN modelling approach for this purpose. The BN was able to model effects of climate change and management on ecological status of a lake, by combining scenarios, process-based model output, monitoring data and the national lake assessment system. The results showed that the benefits of better land-use management were partly counteracted by future warming under these scenarios. Most importantly, the BN demonstrated the importance of including more biological indicators in the modelling of lake status: namely, that inclusion of cyanobacteria biomass can lower the ecological status compared to assessment by phytoplankton biomass alone. Thus, the BN approach can be a useful supplement to process-based models for water resource management.


Noges, P., Argillier, C., Borja, A., Garmendia, J. M., Hanganu, J., Kodes, V., Pletterbauer, F., Sagouis, A., Birk, S. (2016). Quantified biotic and abiotic responses to multiple stress in freshwater, marine and ground waters. Science of the Total Environment 540, 43-52, http://dx.doi.org/10.1016/j.scitotenv.2015.06.045

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Quantified biotic and abiotic responses to multiple stress in freshwater, marine and ground waters

We reviewed 219 papers and built an inventory of 532 items of ecological evidence on multiple stressor impacts in rivers, lakes, transitional and coastal waters, as well as groundwaters. Our review revealed that, despite the existence of a huge conceptual knowledge base in aquatic ecology, few studies actually provide quantitative evidence on multi-stress effects. Nutrient stress was involved in 71% to 98% of multi-stress situations in the three types of surface water environments, and in 42% of those in groundwaters. However, their impact manifested differently along the groundwater-river-lake-transitional-coastal continuum, mainly determined by the different hydro-morphological features of these ecosystems. The reviewed papers addressed two-stressor combinations most frequently (42%), corresponding with the actual status-quo of pressures acting on European surface waters as reported by the Member States in the WISE WFD Database (EEA, 2015). Across all biological groups analysed, higher explanatory power of the stress-effect models was discernible for lakes under multi-stressor compared to single stressor conditions, but generally lower for coastal and transitional waters. Across all aquatic environments, the explanatory power of stress-effect models for fish increased when multi-stressor conditions were taken into account in the analysis, qualifying this organism group as a useful indicator of multi-stress effects. In contrast, the explanatory power of models using benthic flora decreased under conditions of multiple stress.


Nõges, P., Cremona, F., Laas, A., Martma, T., Rõõm, E.-I., Toming, K., Viik, M., Vilbaste, S., Nõges, T. (2016). Role of a productive lake in carbon sequestration within a calcareous catchment. Science of the Total Environment 550, 225–230, http://dx.doi.org/10.1016/j.scitotenv.2016.01.088

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Role of a productive lake in carbon sequestration within a calcareous catchment

For a long time, lakes were considered unimportant in the global carbon (C) cycle because of their small total area compared to the ocean. Over the last two decades, a number of studies have highlighted the important role of lakes in both sequestering atmospheric C and modifying the C flux from the catchment by degassing CO2 and methane and burying calcite and organic matter in the sediment. Based on a full C mass balance, high frequency measurements of lake metabolism and stable isotope analysis of a large shallow eutrophic lake in Estonia, we assess the role alkaline lakes play in augmenting the strength of terrestrial carbonate weathering as a temporary CO2 sink. We show that a large part of organic C buried in the sediments in this type of lakes originates from the catchment although a direct uptake from the atmosphere during periods of intensive phytoplankton growth in eutrophic conditions contributes to the carbon sink.


Nõges, T., Järvalt, A., Haberman, J., Zingel, P., Nõges, P. (2016). Is fish able to regulate filamentous blue-green dominated phytoplankton? Hydrobiologia 780(1), 59-69, http://dx.doi.org/10.1007/s10750-016-2849-9

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Is fish able to regulate filamentous blue-green dominated phytoplankton? 

Efficient zooplankton grazing is a prerequisite for establishing a cascading food web control over phytoplankton in a lake. We studied if the top-down impact of fish could reach phytoplankton in a lake where the grazing pressure of small-sized zooplankton on filamentous phytoplankton is considered weak. We analysed >30 years of data on plankton, fish catches, hydrochemistry, hydrology, and meteorology from Võrtsjärv, a large and shallow eutrophic lake in Estonia with intensive commercial fisheries. The lake’s unregulated water level has been considered the strongest factor affecting the ecosystem through modifying sediment resuspension, internal loading of nutrients, and underwater light conditions and spawning conditions for fish. We found a negative relationship between phytoplankton biomass and pikeperch biomass indicating a potential top-down cascading effect in the food web. Top-down control of phytoplankton by zooplankton was reflected in a negative relationship between phyto- and zooplankton biomasses. A decrease of the individual weight of crustacean zooplankton with increasing biomass of small fish suggested top-down control of zooplankton by planktivorous fish. In contrast, we could not demonstrate a direct linkage between piscivorous fish and small fish. The top-down food web impact of piscivores, however, was manifested at zooplankton level in a positive correlation of pikeperch biomass with the biomass of dominating cladoceran species Bosmina coregoni and the individual weight of copepods. At high biomasses of small fish, ciliate domination over metazooplankton increased and thus enhanced the strength of the microbial food web. According to our results, fishery management measures that increase small plankti- and benthivorous fish biomass have to be avoided as they have a cascading negative effect on the ecosystem health.


Özkan, K., Jeppesen, E., Davidson, T. A., Bjerring, R., Johansson, L. S., Søndergaard, M., Lauridsen, T. L. & Svenning, J.-C. (2016)Long-Term Trends and Temporal Synchrony in Plankton Richness, Diversity and Biomass Driven by Re-Oligotrophication and Climate across 17 Danish Lakes, Water 8, online, http://dx.doi.org/10.3390/w8100427

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Long-Term Trends and Temporal Synchrony in Plankton Richness, Diversity and Biomass Driven by Re-Oligotrophication and Climate across 17 Danish Lakes

A two-decade (1989–2008) time series of lake phyto-and zooplankton, water characteristics and climate in 17 Danish lakes was analysed to examine the long term changes and the effects of lake restoration efforts. The analyses of the pair-wise correlations across time series revealed a strong synchrony in climatic variables among the lakes. A significant, but weak increase in air temperature was observed and resulted in a corresponding increase in surface water temperature only in summer. Lake physico-chemical variables had weaker synchrony than climatic variables. Synchrony in water temperature and stratification was stronger than lake chemistry as the former is mostly affected by atmospheric energy flux. Synchrony in the taxonomic richness of the plankton groups and phytoplankton biomass was apparent, to a similar degree as observed for lake chemistry. The synchrony and the temporal trends in lake chemistry and plankton were more pronounced for the lakes with strong re-oligotrophication. Phytoplankton biomass decreased and plankton richness increased in these lakes, with a shift from Chlorophyta dominance towards more heterogeneous phytoplankton communities. Notably, a widespread significant positive trend in plankton richness was observed not only in lakes with strong re-oligotrophication but across all lakes. The widespread increase in plankton richness coincided with widespread decrease in phosphate and total nitrogen concentrations, as well as with the trends in climate indicating a likely joint effect of nutrient reduction and climate in driving lake plankton. However, temporal changes and synchrony as well as the recovery of richness and composition of lake plankton more coherently corresponded with the nutrient loading reduction across the Danish landscape, while the role of climate control of the lake plankton was less pronounced.


Rankinen, K., Butterfield, D., Faneca Sanchez, M., Grizzetti, B., Whitehead, P., Pitkanen, T., Uusi-Kamppa, J., Leckie, H. (2016). The INCA-Pathogens model: An application to the Loimijoki River basin in Finland. Science of the Total Environment 572, 1611-1621, http://dx.doi.org/10.1016/j.scitotenv.2016.05.043

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The INCA-Pathogens model: An application to the Loimijoki River basin in Finland

Good hygienic quality of surface waters is essential for drinking water production, irrigation of crops and recreation. Predictions of how and when microbes are transported by rivers are needed to protect downstream water users. In this study we tested the new process-based INCA-Pathogens model in the agricultural Loimijoki River basin (3138km(2)) in Finland, and we quantified ecosystem services of water purification and water provisioning for drinking and recreation purposes under different scenarios. INCA is a catchment scale process based model to calculate pollutant transfer from terrestrial environment and point sources to the catchment outlet. A clear gradient was observed in the numbers of faecal coliforms along the River Loimijoki. The highest bacterial counts were detected in the middle part of the main stream immediately after small industries and municipal sewage treatment plants. In terms of model performance, the INCA-Pathogen model was able to produce faecal coliform counts and seasonality both in the low pollution level sampling points and in the high pollution level sampling points. The model was sensitive to the parameters defining light decay in river water and in soil compartment, as well as to the amount of faecal coliforms in the manure spread on the fields. The modeling results showed that the number of faecal coliforms repeatedly exceeded 1000 bacteria 100ml(-1). Moreover, results lead to the following conclusions: 1) Climate change does not cause a major threat to hygienic water quality as higher precipitation increases runoff and causes diluting effect in the river, 2) Intensification of agriculture is not a threat as long as animal density remains relatively low and environmental legislation is followed, 3) More intensive agriculture without environmental legislation causes a threat especially in tributaries with high field percentage and animal density, and 4) Hygienic water quality in the River Loimijoki can best be improved by improving sewage treatment. We conclude that this catchment scale model is a useful tool for addressing catchment management and water treatment planning issues.


Rääpysjärvi,, J., Hämäläinen, H., Aroviita, J. (2016) Macrophytes in boreal streams: Characterizing and predicting nativeoccurrence and abundance to assess human impact, Ecological Indicators 64, 309-318, http://dx.doi.org/ 10.1016/j.ecolind.2016.01.014

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Macrophytes in boreal streams: Characterizing and predicting native occurrence and abundance to assess human impact

Macrophytes are a structurally and functionally essential element of stream ecosystems and therefore indispensable in assessment, protection and restoration of streams. Modelling based on continuous environmental gradients offers a potential approach to predict natural variability of communities and thereby improve detection of anthropogenic community change. Using data from minimally disturbed streams, we described natural macrophyte assemblages in pool and riffle habitats separately and in combination, and explored their variation across large scale environmental gradients. Specifically, we developed RIVPACS-type models to predict the presence and abundance of macrophyte taxa at stream sites in the absence of human influence and, used data from impacted streams to explore the responses of three biotic indices to anthropogenic stress. The indices used, taxonomic completeness (O/E-taxa), a measure of compositional dissimilarity (BC-index) and an index taking into account the abundance of species (AB-index), are based on predicted and observed macrophyte communities. We found that size of the catchment area, altitude, latitude and percentage of lakes in the catchment were the large scale environmental variables that best predicted the natural variation of assemblages. The RIVPACS approach substantially improved both the precision and accuracy to predict the natural communities and the sensitivity to human disturbance. O/E-taxa performed best in relation to the null model decreasing the variation by 20% in pools, 29% in riffles and 32% in combined data. In general, models based on the riffle assemblages performed better than models based on pool assemblages, but including both habitats and predicting abundances instead of only presence/absence yielded the greatest accuracy and sensitivity. Our results support the use of multivariate modelling techniques in predicting reference condition to assess status of stream macrophyte communities.


Rolighed, J., Jeppesen, E., Søndergaard, M., Bjerring, Janse, J. H., Mooij, W. M., Trolle, D. (2016) Climate Change Will Make Recovery from Eutrophication More Difficult in Shallow Danish Lake Søbygaard, Waters 8, online, http://dx.doi.org/10.3390/w8100459

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Climate Change Will Make Recoveryfrom Eutrophication More Difficult in Shallow Danish Lake Søbygaard

Complex lake ecosystem models can assist lake managers in developing management plans counteracting the eutrophication symptoms that are expected to be a result of climate change. We applied the ecological model PCLake based on 22 years of data from shallow, eutrophic Lake Søbygaard, Denmark and simulated multiple combinations of increasing temperatures (0–6 °C), reduced external nutrient loads (0%–98%) with and without internal phosphorus loading. Simulations suggest nitrogen to be the main limiting nutrient for primary production, reflecting ample phosphorus release from the sediment. The nutrient loading reduction scenarios predicted increased diatom dominance, accompanied by an increase in the zooplankton:phytoplankton biomass ratio. Simulations generally showed phytoplankton to benefit from a warmer climate and the fraction of cyanobacteria to increase. In the 6 °C warming scenario, a nutrient load reduction of as much as 60% would be required to achieve summer chlorophyll-a levels similar to those of the baseline scenario with present-day temperatures.


Sagouis, A., Jabot, F., Argillier, C. (2016). Taxonomic versus functional diversity metrics: How do fish communities respond to anthropogenic stressors in reservoirs? Ecology of Freshwater Fish, online, http://dx.doi.org/10.1111/eff.12306

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Taxonomic versus functional diversity metrics: How do fish communities respond to anthropogenic stressors in reservoirs?

Biological indicators are frequently used to assess the effects of anthropogenic stressors on freshwater ecosystems. The structure of fish communities and their response to stressors have been commonly described by taxonomic richness, diversity and evenness. More recently, functional structure of communities has also been suggested to be a reliable indicator of disturbance. This article aimed at testing whether taxonomic and functional diversity metrics can provide comparable or complementary information on the response of fish communities to eutrophication and abundance of non-native species in reservoirs. Comparison of the responses of taxonomic and functional diversities to biogeography, habitat and stressors was made in 112 French reservoirs. Widely observed effects of biogeographic and habitat variables on taxonomic and functional diversities were identified. Taxonomic and functional richness metrics notably increased with lake area and temperature respectively. Taxonomic diversity metrics did not respond to any stressor, while all functional diversity metrics were found to be impacted by non-native species. Eutrophication was further found to decrease the impact of non-native species on two functional diversity metrics: evenness and divergence. Our study therefore reveals that functional metrics are more sensitive than taxonomic metrics to anthropogenic stressors in the studied reservoirs. Still, the multiple linear regressions tested had overall low explanatory power. Further refinements will thus be needed to use this type of metrics in an impact assessment scheme.


Schinegger, R., Palta, M., Segurado, P., Schmutz, S. (2016) Untangling the effects of multiple human stressors and their impacts on fish assemblages in European running waters, Sciene of The total Environment, 573, 1079-1088, http://dx.doi.org/10.1016/j.scitotenv.2016.08.143

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Untangling the effects of multiple human stressors and their impacts on fish assemblages in European running waters

This work addresses human stressors and their impacts on fish assemblages at pan-European scale by analysing single and multiple stressors and their interactions. Based on an extensive dataset with 3105 fish sampling sites, patterns of stressors, their combination and nature of interactions, i.e. synergistic, antagonistic and additive were investigated. Geographical distribution and patterns of seven human stressor variables, belonging to four stressor groups (hydrological-, morphological-, water quality- and connectivity stressors), were examined, considering both single and multiple stressor combinations. To quantify the stressors' ecological impact, a set of 22 fish metrics for various fish assemblage types (headwaters, medium gradient rivers, lowland rivers and Mediterranean streams) was analysed by comparing their observed and expected response to different stressors, both acting individually and in combination. Overall, investigated fish sampling sites are affected by 15 different stressor combinations, including 4 stressors acting individually and 11 combinations of two or more stressors; up to 4 stressor groups per fish sampling site occur. Stressor-response analysis shows divergent results among different stressor categories, even though a general trend of decreasing ecological integrity with increasing stressor quantity can be observed. Fish metrics based on density of species ‘intolerant to water quality degradation’ and ‘intolerant to oxygen depletion” responded best to single and multiple stressors and their interactions. Interactions of stressors were additive (40%), synergistic (30%) or antagonistic (30%), emphasizing the importance to consider interactions in multi-stressor analyses. While antagonistic effects are only observed in headwaters and medium-gradient rivers, synergistic effects increase from headwaters over medium gradient rivers and Mediterranean streams to large lowland rivers. The knowledge gained in this work provides a basis for advanced investigations in European river basins and helps prioritizing further restoration and management actions.


Schülting, L., Feld, C. K., Graf, W. (2016) Effects of hydro- and thermopeaking on benthic macroinvertebrate drift, Science of The Total Environment (in press), http://dx.doi.org/10.1016/j.scitotenv.2016.08.022

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Effects of hydro- and thermopeaking on benthic macroinvertebrate drift

The operation of storage hydropower plants is commonly linked to frequent fluctuations in discharge and water level (hydropeaking) of downstream river stretches and is often accompanied by cooling or warming of the water body downstream (cold or warm thermopeaking, respectively). The objective of this study is to assess the single and combined effects of hydropeaking and cold thermopeaking on the drift of selected aquatic macroinvertebrates in experimental flumes. The study specifically aims to (1) investigate the macroinvertebrate drift induced by hydropeaking, (2) identify taxon-specific drift patterns following combined hydropeaking and cold thermopeaking and (3) quantify diurnal drift differences under both impact types. Overall, hydropeaking induced significantly higher drift rates of most macroinvertebrate taxa. Combined hydropeaking and cold thermopeaking, however, revealed reduced total drift rates, however with strong taxon-specific response patterns. Hydropeaking during night led to significantly higher drift rates than during daytime, while in combination with thermopeaking the same trend was observable, although insignificant. Taxon-specific analysis revealed lower drift rates following hydropeaking for rheophilic and interstitial taxa (e.g. Leuctra sp., Hydropsyche sp.), whereas many limnophilic taxa adapted to low current showed markedly increased drift (e.g. Lepidostoma hirtum and Leptoceridae). In line with previous studies, our results confirm a significant loss of limnophilic macroinvertebrate taxa following hydraulic stress. The mitigating effect of cold thermopeaking might be explained by behavioural patterns, but requires further investigation to clarify if macroinvertebrates actively avoid drift and intrude into the interstitial, when cold water is discharged. Our results imply that river restoration projects must address the hydrological regime and, if necessary need to include suitable management schemes for hydropower plants. Besides operative management measures, the construction of reservoirs to buffer hydropeaks or the diversion of hydropeaks into larger water bodies could mitigate hydropeaking effects and foster biological recovery including limnophilic taxa.


Søndergaard, M., Larsen, S. E., Johansson, L. S., Lauridsen T. L., Jeppesen, E. (2016). Ecological classification of lakes: Uncertainty and the influence of year-to-year variability. Ecological Indicators 61, 248- 257, http://dx.doi.org/10.1016/j.ecolind.2015.09.024

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Ecological classification of lakes: Uncertainty and the influence of year-to-year variability

Regular monitoring of lakes is important to determine their ecological state and development and of key significance when deciding whether action should be taken to improve their quality, for instance by reducing the external loading of nutrients. Imprecise or inadequate knowledge of the ecological state increases the risk of misclassification and of wrong management decisions. Based on Danish lake data, we aimed to determine temporal variations, in particular natural year-to-year differences, and to describe the uncertainty in assessing the ecological state of lakes. We analysed environmental data from ca. 350 Danish lakes (1100 lake years), including three case studies, with long-term data series (up to 24 years), with no significant changes in external nutrient loading. We used summer means of selected water chemical variables, phytoplankton and submerged macrophytes as indicators of ecological state and found considerable variations in all indicators, which could not be ascribed alone to meteorological variation. In shallow lakes, chlorophyll a concentrations exhibited large year-to-year variations, especially at TP ranging between 0.05 and 0.15 mg L −1 where the lakes may shift between a macrophyte-and a phytoplankton-dominated state. For example, chlorophyll a varied by a factor 5–10 between years and was particularly low when submerged macrophyte coverage exceeded 20% compared with lakes without macrophytes. Use of a multimetric index including four phytoplankton indicators reduced the coefficient of variation. Generally, the 95% confidence interval of ecological classification was approximately 50% lower when the assessment of ecological state was based on 4–5 years' measurements than if based on only one year's measurements. Knowledge and awareness of the uncertainty of indicators used in ecological classification are highly relevant for lake managers and policy makers when defining efficient monitoring and restoration strategies.


Spears, B. M., Carvalho, L., Futter, M. N., May, L., Thackeray, S. J., Adrian, R., D. Angeler, G., Burthe, S. J., Davidson, T. A., Daunt, F., Gsell, A. S., Hessen, D. O., Moorhouse, H., Huser, B., Ives, S. C., Janssen, A. B., Mackay, E. B., Sondergaard, M., Jeppesen, E. (2016). Ecological Instability in Lakes: A Predictable Condition? Environmental Science & Technology 50(7), 3285-3286, http://dx.doi.org/10.1021/acs.est.6b00865

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Ecological Instability in Lakes: A Predictable Condition?

Society is threatened with an increased likelihood of unexpected and rapid loss of natural capital, increased public health risk from toxic cyanobacteria, and loss of biodiversity in lakes. Observations and models reveal that lakes can exhibit sudden, but persistent, ecological changes preceded by the erosion of ecological stability (e.g. phenomenon of ‘flickering’ or ‘critical slowing down’1) driven by extrinsic (e.g. extreme weather events) or intrinsic (e.g. trophic interactions) pressures. This evidence is being used to develop the basis for resilience based management across other ecosystem types. However, although slow (i.e. years to centuries), ecological responses following abatement of dominant pressures are well documented (e.g. catchment nutrient load reduction2), the same cannot be said for sudden ecological transitions (i.e. < 1 year duration). This leads to a lack of confidence in predicting such events and an inability to prevent them. This is challenging given the practical need for early detection of ecological instability required to support effective preventative management. Recent advances across three fields of freshwater ecology offer opportunities to address this issue. These include (1) detecting critical pressure thresholds using data from large populations of lakes; (2) examining the causes, forms and rates of change during past events using long-term contemporary and palaeolimnological data, and (3) using high-frequency monitoring to predict sudden transitions using statistical analogues of ecosystem stability. We offer recommendations for their use in diagnosing ecological instability in lakes. Critical Thresholds from Multi-Lake Data Following the implementation of national scale water quality assessment programmes, monitoring data from many thousands of lakes are available over short periods (i.e. < 10 years). The advent of data collection by earth observation systems (e.g. satellite data) offers the possibility to collect data from many lake systems across broader spatial scales. However, while these monitoring data are spatially extensive, many have relatively coarse (seasonal or annual) temporal resolution and cover few ecological indicators; this limits the application of time-series analysis to the detection of short-term ecological events. Subsets of these data have been used to determine regional or national scale physico-chemical thresholds (e.g. water temperature; nutrients) that, when crossed, may cause major reorganization of ecological structure and function. Such thresholds are poor predictors of change in single lakes and provide limited insights into the importance of intrinsic pressures, although they can provide early warning (i.e. annual resolution) of ecological deterioration across lake districts using emerging approaches such as discontinuity analysis3. Detecting variability in multi-lake responses across these thresholds should be further developed to include multiple interactive pressure scenarios. As global earth observation data are made publically available (i.e. within 5 to 10 years) our ability to quantify such thresholds will be enhanced. Assessing Past Events Using Palaeolimnology Paleolimnological approaches can extend the relatively limited time-period of many contemporary monitoring datasets to centuries or millennia. When combined with documented pressure changes, for example by using contemporary long-term monitoring data, these approaches have provided evidence of variable rates of ecological responses to pressures (from years to centuries) and of ‘ecological reorganisation’ across whole foodwebs. Attempts to develop forecasting approaches by quantifying changes in ecological stability using lead indicators (e.g. evidence of ‘flickering’ between alternative stable states in diatom fossils <30 years prior to a transition3), have been contentious. Due to the nature of bed sediment processes, this approach offers limited temporal resolution with which subtle short-term (i.e. days to months) changes in ecological stability can be detected. However, given that the sediment record reflects a concentration of the communities above it, it offers high ecological resolution that enables shifts in communities and foodwebs to be detected retrospectively. We call for the development of robust quantitative approaches that provide timelines for ecological responses across multiple trophic levels and relate these to changes in the antecedent behaviour of paleolimnological indicators. Early Warning Indicators (EWIs) of Ecological Transitions Long-term (20+ year) water chemistry and ecological monitoring data are publicly available for < 0.1% of the world’s 117 million lakes. However, the available data provide an important resource enabling ecological transitions to be studied in detail, and at relatively high frequencies (typically, weekly to monthly). As with paleolimnological examples, evidence of sudden ecological shifts in these data have been documented mainly as dramatic regime shifts with any links to changes in extrinsic and intrinsic pressures being mostly qualitative. The use of temporal changes in the statistical properties of ecological time-series (e.g. increased autocorrelation or variance) as indicators of changes in stability have a strong theoretical basis, even though tests on data from ecosystem experiments at various scales have given ambiguous results. Assuming that there is fundamental ecological reorganisation at the time of a critical transition, one would expect temporal fluctuations to propagate throughout ecological communities and be detectable across multiple species. However, to date, the application of EWIs to long time-series that exhibit non-linear changes has been unconvincing4, indicating that either changes in system stability are not common, or that we cannot yet detect them with confidence in the available data. Recent large scale experiments that have used high frequency (i.e. seconds to minutes) automated monitoring systems to determine the effects of perturbations on ecological stability have demonstrated variable success across multiple EWIs5. Results of such experiments must undergo objective real world validation across multiple lakes, which may take decades to accomplish. However, through the application of mechanistic models, wide scale changes in physical processes (e.g. loss of ice cover) can be predicted. This offers opportunities for the effects of natural phenomenon on ecological stability to be observed, or future experimental treatments to be developed. Is Prediction of Ecological Transitions Achievable? While theory on ecosystem changes preceding an ecological transition is well-developed, the more practical “proof of concept” has been unconvincing so far. This is unfortunate, because costly preventative management approaches must be based on irrefutable evidence. To provide better information for managers, we propose that (1) the frequency of occurrence, forms and rates of change during transitions in multiple ecological indicators be quantified in publicly available, long-term and spatially extensive data and that drivers of variation be determined, (2) the analysis of ecological community behaviour preceding and following transitions should be developed (i.e. objective analysis of early warning) alongside procedures for the application and interpretation of EWIs and confidence ratings, and (3) the occurrence of ecological instability in lakes should be demonstrated irrefutably using replicated field scale experiments, including measures for the control of intrinsic and extrinsic processes that are designed to prevent or cause a transition. 


Stefanidis, K., Panagopoulos, Y., Mimikou, M. (2016). Impact assessment of agricultural driven stressors on benthic macroinvertebrates using simulated data. Science of the Total Environment 540, 32-42, http://dx.doi.org/10.1016/j.scitotenv.2015.08.015

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Impact assessment of agricultural driven stressors on benthic macroinvertebrates using simulated data

Agricultural land use poses a significant threat to the ecological integrity of rivers in Europe. Particularly in the Mediterranean, water abstraction and nutrient application are anthropogenic pressures that have a significant impact on aquatic habitats and biodiversity. In this article, we assessed the effects of agricultural management practices on benthic macroinvertebrates in a large river basin of central Greece using simulated data based on the application of SWAT (Soil Water Assessment Tool) model. Physicochemical and hydrological output variables of the model were used as predictors of the ASPT (Average Score Per Taxon) metric based on a correlated component regression analysis (CCR) built on empirical data. The estimation of ASPT was performed for the wet and dry seasons within a 20-year period for a total of 47 subbasins under the baseline conditions and after implementing three management scenarios that reduced: a) irrigation water applied to crops by 30%, b) chemical fertilization applied to crops by 30% and c) both irrigation and fertilization by 30%. The results revealed that application of the reduced irrigation resulted to a slight increase of the simulated dissolved inorganic nitrogen concentration (DIN), which in turn decreased the mean ASPT in 21 of the 47 subbasins implying a negative effect on the macroinvertebrate communities. On the contrary, the reduction of fertilization as well as the combined scenario decreased both the simulated DIN and phosphate concentration causing an increase of the mean ASPT for a total of 40 of the 47 subbasins. Based on these results, we suggest that the best management option is a combined practice of deficit irrigation and fertilization reduction since it improved water quality, increased ASPT values and saved a considerable amount of water. Overall, this work demonstrates a simple methodology that can efficiently assess the effects of agricultural management practices on biotic indicators.


Stefanidis, K., Panagopoulos, Y., Psomas, A., Mimikou, M. (2016). Assessment of the natural flow regime in a Mediterranean river impacted from irrigated agriculture. Science of the Total Environment 573, 1492-1502, http://dx.doi.org/10.1016/j.scitotenv.2016.08.046

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Assessment of the natural flow regime in a Mediterranean river impacted from irrigated agriculture

Over the last few decades, the natural flow regime of most rivers has been significantly altered influencing the ecological integrity and functioning of river ecosystems. Especially in the Mediterranean region, irrigated agriculture is considered one of the most important drivers of hydro-morphological modifications in river systems. In this study we employ the Indicators of Hydrologic Alteration (IHA) methodology for the Pinios River and its tributaries, located in a Mediterranean catchment in central Greece, with the purpose to assess the natural flow regime under a simulated no-agriculture scenario and compare with the current situation. The work is based on the use of the SWAT (Soil Water Assessment Tool) model for the simulation of long time series of daily stream flows, which were analyzed under the actual conditions (baseline), and the hypothetical scenario. The key characteristics of the flow regime projected under each model run were assessed through the implementation of the IHA methodology that utilizes a number of indicators to characterize the intra- and inter-annual variability in the hydrologic conditions. The results of this study revealed that without agricultural activities in the catchment, annual and monthly flows would increase, with significant alterations in the flow characteristics of the winter months, and much smaller in summer. However, the analysis showed that the frequency of droughts and low flow summer events would be smaller. The article provides a comprehensive and easy-to-implement methodology that can facilitate the impact assessment of agricultural human activities on river flow variability under the typical Mediterranean conditions, allowing experimentation on setting river flow thresholds required for a good ecological status within the context of the European Water Framework Directive.


Taipale, S. J., Vuorio, K., Strandberg, U., Kahilainen, K. K., Jarvinen, M., Hiltunen, M., Peltomaa, E., Kankaala, P. (2016). Lake eutrophication and brownification downgrade availability and transfer of essential fatty acids for human consumption. Environment International 96, 156-166, http://dx.doi.org/10.1016/j.envint.2016.08.018

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Lake eutrophication and brownification downgrade availability and transfer of essential fatty acids for human consumption

Fish are an important source of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) for birds, mammals and humans. In aquatic food webs, these highly unsaturated fatty acids (HUFA) are essential for many physiological processes and mainly synthetized by distinct phytoplankton taxa. Consumers at different trophic levels obtain essential fatty acids from their diet because they cannot produce these sufficiently de novo. Here, we evaluated how the increase in phosphorus concentration (eutrophication) or terrestrial organic matter inputs (brownification) change EPA and DHA content in the phytoplankton. Then, we evaluated whether these changes can be seen in the EPA and DHA content of piscivorous European perch (Perca fluviatilis), which is a widely distributed species and commonly consumed by humans. Data from 713 lakes showed statistically significant differences in the abundance of EPA- and DHA-synthesizing phytoplankton as well as in the concentrations and content of these essential fatty acids among oligo-mesotrophic, eutrophic and dystrophic lakes. The EPA and DHA content of phytoplankton biomass (mg HUFA g− 1) was significantly lower in the eutrophic lakes than in the oligo-mesotrophic or dystrophic lakes. We found a strong significant correlation between the DHA content in the muscle of piscivorous perch and phytoplankton DHA content (r = 0.85) as well with the contribution of DHA-synthesizing phytoplankton taxa (r = 0.83). Among all DHA-synthesizing phytoplankton this correlation was the strongest with the dinoflagellates (r = 0.74) and chrysophytes (r = 0.70). Accordingly, the EPA + DHA content of perch muscle decreased with increasing total phosphorus (r2 = 0.80) and dissolved organic carbon concentration (r2 = 0.83) in the lakes. Our results suggest that although eutrophication generally increase biomass production across different trophic levels, the high proportion of low-quality primary producers reduce EPA and DHA content in the food web up to predatory fish. Ultimately, it seems that lake eutrophication and brownification decrease the nutritional quality of fish for human consumers.


Teichert, N., Borja, A., Chust, G., Uriate, A., Lepage, M. (2016) Restoring fish ecological quality in estuaries: Implication of interactive and cumulative effects among anthropogenic stressors, Science of the Total Environment 542, 383-393, http://dx.doi.org/10.1016/j.scitotenv.2015.10.068

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Restoring fish ecological quality in estuaries: Implication of interactive and cumulative effects among anthropogenic stressors

Estuaries are subjected to multiple anthropogenic stressors, which have additive, antagonistic or synergistic effects. Current challenges include the use of large databases of biological monitoring surveys (e.g. the European Water Framework Directive) to help environmental managers prioritizing restoration measures. This study investigated the impact of nine stressor categories on the fish ecological status derived from 90 estuaries of the North East Atlantic countries. We used a random forest model to: 1) detect the dominant stressors and their non-linear effects; 2) evaluate the ecological benefits expected from reducing pressure from stressors; and 3) investigate the interactions among stressors. Results showed that largest restoration benefits were expected when mitigating water pollution and oxygen depletion. Non-additive effects represented half of pairwise interactions among stressors, and antagonisms were the most common. Dredged sediments, flow changes and oxygen depletion were predominantly implicated in non-additive interactions, whereas the remainder stressors often showed additive impacts. The prevalence of interactive impacts reflects a complex scenario for estuaries management; hence, we proposed a step-by-step restoration scheme focusing on the mitigation of stressors providing the maximum of restoration benefits under a multi-stress context.


Toming, K., Kutser, T., Tuvikene, L., Viik, M., Nõges, T. (2016). Dissolved organic carbon and its potential predictors in large shallow eutrophic temperate lake. Water Research 102, 32-40, http://dx.doi.org/10.1016/j.watres.2016.06.012

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Dissolved organic carbon and its potential predictors in large shallow eutrophic temperate lake

Understanding of the true role of lakes in the global carbon cycle requires reliable estimates of dissolved organic carbon (DOC) and there is a strong need to develop remote sensing methods for mapping lake carbon content at larger regional and global scales. Part of DOC is optically inactive. Therefore, lake DOC content cannot be mapped directly. The objectives of the current study were to estimate the relationships of DOC and other water and environmental variables in order to find the best proxy for remote sensing mapping of lake DOC. The Boosted Regression Trees approach was used to clarify in which relative proportions different water and environmental variables determine DOC. In a studied large and shallow eutrophic lake the concentrations of DOC and coloured dissolved organic matter (CDOM) were rather high while the seasonal and interannual variability of DOC concentrations was small. The relationships between DOC and other water and environmental variables varied seasonally and interannually and it was challenging to find proxies for describing seasonal cycle of DOC. Chlorophyll a (Chl a), total suspended matter and Secchi depth were correlated with DOC and therefore are possible proxies for remote sensing of seasonal changes of DOC in ice free period, while for long term interannual changes transparency-related variables are relevant as DOC proxies. CDOM did not appear to be a good predictor of the seasonality of DOC concentration in Lake Võrtsjärv since the CDOM–DOC coupling varied seasonally. However, combining the data from Võrtsjärv with the published data from six other eutrophic lakes in the world showed that CDOM was the most powerful predictor of DOC and can be used in remote sensing of DOC concentrations in eutrophic lakes.


Turunen, J., Muotka, T., Vuori, K-M., Karjalainen, S.M., Rääpysjärvi, J., Sutela, T. & Aroviita, J. (2016) Disentangling the responses of boreal stream assemblages to low stressor levels of diffuse pollution and altered channel morphology, Science of the Total Environment 544, 954–962, http://dx.doi.org/10.1016/j.scitotenv.2015.12.031

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Disentangling the responses of boreal stream assemblages to low stressor levels of diffuse pollution and altered channel morphology

Non-point diffuse pollution from land use and alteration of hydromorphology are among the most detrimental stressors to stream ecosystems. We explored the independent and interactive effects of morphological channel alteration (channelization for water transport of timber) and diffuse pollution on species richness and community structure of four organism groups in boreal streams: diatoms, macrophytes, macroinvertebrates, and fish. Furthermore, the effect of these stressors on stream condition was evaluated by Ecological Quality Ratios (EQR) from the national Water Framework Directive (WFD) assessment system. We grouped 91 study sites into four groups that were impacted by either diffuse pollution or hydromorphological alteration, by both stressors, or by neither one. Macroinvertebrate richness was reduced by diffuse pollution, whereas other biological groups were unaltered. Hydromorphological modification had no effect on taxon richness of any of the assemblages. Community structure of all groups was significantly affected by diffuse pollution but not by hydromorphology. Similarly, EQRs indicated negative response by diatoms, macroinvertebrates and fish to diffuse pollution, but not to hydromorphological alteration. Agricultural diffuse pollution thus affected species identities and abundances rather than taxonomic richness. Our results suggest that channelization of boreal streams for timber transport has not altered hydromorphological conditions sufficiently to have a strong impact on stream biota, whereas even moderate nutrient enrichment may be ecologically harmful. Controlling diffuse pollution and associated land use stressors should be prioritized over restoration of in-stream habitat structure to improve the ecological condition of boreal streams.


Ventelä, A.-M., Amsinck, S.L., Kauppila, T., Johansson, L. S., Jeppesen, E., Kirkkala, T., Søndergaard, M., Weckström, J. & Sarvala, J. (2016) Ecosystem changes in large and shallow Lake Säkylän Pyhäjärvi, Finland, during the past 400 years - implications for management, Hydrobiologia 778, 273-294, http://dx.doi.org/10.1007/s10750-015-2552-2

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Ecosystem change in the large and shallow Lake Säkylän Pyhäjärvi, Finland, during the past ~400 years: implications for management

Lake Säkylän Pyhäjärvi has been an important fishing site and drinking water source for the local population for centuries. The lake has undergone significant changes: (1) the water level was lowered in the 1600s and in the 1850s; (2) planktivorous coregonid fish were successfully introduced in the early 1900s; (3) nutrient input from intensified agriculture has increased since the 1950s and (4) the effects of the current variable climate on the lake and its catchment have become more evident since the 1990s. We determined the phases of oligotrophication, eutrophication and recovery and elucidated the ecosystem changes by combining palaeolimnological records with detailed neolimnological data. The sedimentary diatom and cladoceran assemblages first showed a relatively eutrophic period followed by oligotrophic periods, linked with the artificial changes in water level and consequent shifts in macrophyte abundance. The oligotrophic period in the early 1900s is thought to represent the target trophic state for the lake. After the 1950s, introduction of vendace resulted in higher planktivory reflected by an increased relative abundance of small-bodied pelagic cladocerans. Signs of eutrophication occurred due to increased nutrient load. During the last 10 years, signs of recovery have been recorded. A complex history such as that of Lake Pyhäjärvi illustrates the difficulties in selecting management targets, and the risk of setting false targets, for lakes based solely on monitoring data—both neolimnological and palaeolimnological approach are needed.


Vilbaste, S., Järvalt, A., Kalpus, K., Nõges, T., Pall, P., Piirsoo, K., Tuvikene, L. and Nõges, P. (2016). Ecosystem services of Lake Võrtsjärv under multiple stress: A case study. Hydrobiologia 780(1), 145-159, http://dx.doi.org/10.1007/s10750-016-2871-y

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Ecosystem services of Lake Võrtsjärv under multiple stress: A case study

This study is the first attempt at the European scale to make an inventory of ecosystem services (ESS) of a large lake. We analysed a set of ESS indicators against the annual mean values of environmental parameters for 2006–2013. According to principal component analysis, the trophic state- and hydrology-related factors explained about 70% of the environmental variability of the lake and showed strong relationships with some ESS. Among the provisioning ESS, the annual eel catch and the total fish catch were positively related to different eutrophication indicators while the catches of pike, bream, and burbot depended rather on hydrological factors. Reed harvesting efficiency was related to the lake’s water level. The indicators of regulating, maintenance, and cultural ESS showed very high variability in different years, the latter depending on socio-economic conditions rather than environmental factors. We discovered numerous trade-offs between ESS benefitting from higher trophic state or regulated water level of the lake and the goals of good ecological status of the lake. Our analysis showed a clear need for rules prioritizing life supporting regulatory services against other ESS.


Vilmi, A., Karjalainen, S. M., Hellsten, S., Heino, J. (2016). Bioassessment in a metacommunity context: Are diatom communities structured solely by species sorting? Ecological Indicators 62, 86–94, http://dx.doi.org/10.1016/j.ecolind.2015.11.043

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Bioassessment in a metacommunity context: Are diatom communities structured solely by species sorting?

Aquatic ecosystems face a variety of anthropogenic pressures, urging the development of efficient biological indicators. In addition to local environmental conditions, the community structure of indicator organisms is affected by spatial processes, such as high and limited dispersal rates. Understanding the relative roles of environmental factors and spatial processes for ecological communities should thus be associated with bioassessment practices. We examined the main drivers, both environmental and spatial, influencing community structure and several indices derived from diatom communities. We sampled 81 stony littoral sites in a large boreal lake system (305 km 2), where relatively large gradients in water chemistry (35 variables measured) exist, but no dispersal limitation can be expected. Instead, high dispersal rates should interfere with species sorting. Our response variables, including commonly-used diatom indices, diversity indices and taxonomic distinctness indices, were better explained by pure effects of spatial variables and shared effects of spatial and environmental variables than by pure effects of environmental variables. Thus, high dispersal rates between sites are likely to interfere with environmental filtering and can result in clear spatial structures in index values used in bioassessment. Bioassessment should thus acknowledge the importance of spatial processes and not take it for granted that only local environmental conditions determine index values. Failure to consider high dispersal rates may lead to biased information about the state of freshwater ecosystems. The same idea should also be considered in systems with similarly highly-connected sets of bioassessment sites, such as marine coastal systems and stream networks.


Whitehead, P. G., Bussi, G., Bowes, M., Read, D., Dadson, S., Elliot, A. (2016). Dynamic Modelling of Multiple Phytoplankton Groups in Rivers with an Application to the Thames River System in the UK. Science of the Total Environment 74, 75-91, http://dx.doi.org/10.1016/j.envsoft.2015.09.010

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Dynamic Modelling of Multiple Phytoplankton Groups in Rivers with an Application to the Thames River System in the UK

A process-based phytoplankton model developed to simulate the movement and growth of phytoplankton in river systems is presented in this paper. The model is based on mass-balance, and takes into account water temperature, light, self-shading, dissolved phosphorus and silicon concentrations. It was implemented in five reaches of the River Thames (UK), and the results compared to a novel dataset of cytometric data which includes concentrations of chlorophytes, diatoms, cyanobacteria and picoalgae. A Multi-Objective General Sensitivity Analysis was carried out in order to test the model robustness and to quantify the sensitivity to its parameters. The results show a good agreement between the simulations and the measured phytoplankton abundance. The most influential parameters were phytoplankton growth and death rates, while phosphorus concentration showed little influence, due to the high concentration of phosphorus in the Thames. The model is an important step forward towards understanding and predicting algal dynamics in river systems.


Wiegleb, G., Gebler, D., de Weyer, K., Birk, S. (2016) Comparative test of ecological assessment methods of lowland streams based on long-term monitoring data of macrophytes, Science of The Total Environment 541, 1269–1281, http://dx.doi.org/10.1016/j.scitotenv.2015.10.005

ResearchGate
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Comparative test of ecological assessment methods of lowland streams based on long-term monitoring data of macrophytes

Ecological assessment of water courses is required by the European Water Framework Directive (WFD). Assessment by means of macrophytes is impeded by insufficient knowledge on the relations between assessment scores and the dynamics of environmental parameters. Data from a long-term observation of macrophyte dynamics over 21years in two lowland rivers were used for testing the performance of six widely used assessment methods. Six sample sites situated in two lowland streams were selected. Four sites were classified as of moderate habitat quality and two sites as of poor habitat quality in the context of WFD. Assessment methods generally showed a poor performance in recognizing the ecological status of the annual observations. Status was more often over- than underestimated. Performance of methods differed among individual rivers and among river zones. Assessment scores mostly showed a steady decline, even though all sites obviously remained in the same habitat quality class throughout the observation period. Variation of most environmental factors was largely unrelated to assessment scores. Fluctuations of assessment scores were partly related to single natural disturbance events such as high discharge. Increased shading by marginal trees was reflected negatively by most assessment scores. Assessment scores were highly correlated with species richness and total abundance. The best overall performance was shown by the North-Rhine Westphalian (NRW) method. In contrast to single metric methods it can be adapted to individual properties of a reach in a flexible way. Macrophyte assessment based on the pressure-impact framework did not lead to a satisfying result in our case study. Improvement of species assessment scores and inclusion of functional properties such as growth form may help to overcome the present difficulties.


Wright, R. F., Couture, R.-M., Christiansen, A. B., Guerrero, J.-L., Kaste, Ø., Barlaup. B. T.(2016) Effects of multiple stresses hydropower, acid deposition and climate change on water chemistry and salmon populations in the River Otra, Norway, Science of The Total Environment, 574, 128-138, http://dx.doi.org/10.1016/j.scitotenv.2016.09.044

link to ResearchGate
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Effects of multiple stresses hydropower, acid deposition and climate change on water chemistry and salmon populations in the River Otra, Norway

Many surface waters in Europe suffer from the adverse effects of multiple stresses. The Otra River, southernmost Norway, is impacted by acid deposition, hydropower development and increasingly by climate change. The river holds a unique population of land-locked salmon and anadromous salmon in the lower reaches. Both populations have been severely affected by acidification. The decrease in acid deposition since the 1980s has led to partial recovery of both populations. Climate change with higher temperatures and altered precipitation can potentially further impact fish populations. We used a linked set of process-oriented models to simulate future climate, discharge, and water chemistry at five sub-catchments in the Otra river basin. Projections to year 2100 indicate that future climate change will give a small but measureable improvement in water quality, but that additional reductions in acid deposition are needed to promote full restoration of the fish communities. These results can help guide management decisions to sustain key salmon habitats and carry out effective long-term mitigation strategies such as liming. The Otra River is typical of many rivers in Europe in that it fails to achieve the good ecological status target of the EU Water Framework Directive. The programme of measures needed in the river basin management plan necessarily must consider the multiple stressors of acid deposition, hydropower, and climate change. This is difficult, however, as the synergistic and antagonistic effects are complex and challenging to address with modelling tools currently available.


Yu, J., Liu, Z., He, H., Zhen, W., Guan, B., Chen, F., Li, K., Zhong, P., Teixeira-de Mello, F. & Jeppesen, E. (2016) Submerged macrophytes facilitate the omnivorous dominance of fish community in a subtropical shallow lake: implication for shallow lake restoration, Hydrobiologia 775, 97-107, http://dx.doi.org/10.1007/s10750-016-2717-7

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Submerged macrophytes facilitate dominance of omnivorous fish in a subtropical shallow lake: implications for lake restoration

Biomanipulation based on removal of coarse fish, piscivorous fish stocking and sometimes also planting of submerged macrophytes has been used to restore temperate eutrophic shallow lakes. However, in warmer lakes, omnivorous fish are more abundant and apparently less well controlled by the piscivores. We investigated the food web structure and energy pathways of fish in the restored part of subtropical Lake Wuli, China, using gut contents analysis (GCA) and the IsoSource model based on stable isotope analysis (SIA) data. We found that omnivores dominated the fish community in terms of numbers. GCA showed that cyclopoid copepods constituted the main food item for the planktivores, while all adult omnivorous fish fed mainly on macrophytes. The IsoSource SIA model supported these results. Furthermore, piscivores consumed shrimps rather than juvenile omnivores, and the SIA analysis revealed no trophic links between piscivores and adult omnivores or zooplanktivores. We conclude that macrophytes constituted an important food item for omnivores, potentially promoting population growth of omnivores as control by piscivores was weak. This may yield a high predation pressure on both zooplankton and on macrophytes, possibly preventing the establishment of a stable macrophyte state following restoration of eutrophic lakes unless the fish density is regularly controlled.


Yu, J., Liu, Z., Li, K., Chen, F., Guan, B., Hu, Y., Zhong, P., Tang, Y., Zhao, X., He, H., Zeng, H. & Jeppesen, E.(2016) Restoration of Shallow Lakes in Subtropical and Tropical China: Response of Nutrients and Water Clarity to Biomanipulation by Fish Removal and Submerged Plant Transplantation, Water 8 (online), http://dx.doi.org/10.3390/w8100438

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Restoration of Shallow Lakes in Subtropical and Tropical China: Response of Nutrients and Water Clarity to Biomanipulation by Fish Removal and Submerged Plant Transplantation

Fish removal has been used to restore temperate lakes, and positive effects on ecological state and water clarity have frequently been recorded in many lakes. Recently, a supplementary measure, transplantation of submerged macrophytes after fish removal, has been applied to restore warm Chinese shallow lakes in order to compensate for the expected lack of increasing grazing control of phytoplankton after the biomanipulation. These measures have successfully shifted turbid warm lakes to a clear water state, but little is known about the responses to restoration of key physico-chemical variables. We analyzed the seasonal variation in nutrient concentrations in two subtropical and one tropical biomanipulated shallow Chinese lakes subjected to restoration. In all three lakes, a marked decline occurred in the concentrations of lake total nitrogen (TN), total phosphorus (TP), total suspended solids (TSS), and chlorophyll a (Chl a), while the transparency (SD:WD ratio, Secchi depth to water depth ratio) increased. A clear water state was established, lasting so far for 7 to 23 months, and TN, TP, Chl a, and TSS levels in the three restored lakes decreased to, on average, 49%, 58%, 41%, and 18% of the level prior to restoration and/or the level in a reference lake, respectively, while the annual mean SD:WD ratio exhibited a 1.5–4 fold increase. In conclusion, lake restoration by transplantation of submerged macrophytes after fish removal had major positive effects on the physico-chemical variables in our study lakes. However, continuous control of omnivorous and herbivorous fish biomass is recommended as the fish typically present in warm, shallow lakes to some extent feed on submerged macrophytes, when available.


Yu, J., Zhen, W., Guan, B., Zhong, P., Jeppesen, E. & Liu, Z. (2016) Dominance of Myriophyllum spicatum in submerged macrophyte communities associated with grass carp, Knowledge and Management of Aquatic Ecosystems 417, 24, http://dx.doi.org/10.1051/kmae/2016011

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Dominance of Myriophyllum spicatum in submerged macrophyte communities associated with grass carp

Re-establishment of macrophyte communities is a key to restore eutrophic shallow lakes. The species com- position of the plant communities may change rapidly during the recovery period. A basin in subtropical Lake Qinhu (China) was restored by biomanipulation including fish removal followed by planting of submerged macrophytes in 2011. In September-December 2011, dominance of Vallisneria spinulosa and Ceratophyllum demersum shifted to dom- inance of Myriophyllum spicatum. Meanwhile, the CPUE (catch per unit effort) showed that the number and biomass of grass carp (Ctenopharyngodon idella) demonstrated a marked increase. Stable isotope analyses revealed that grass carp preferred V. spinulosa and C. demersum to M. spicatum. We propose that grazing by grass carp was responsible for the observed shift in dominance towards M. spicatum but as alternative explanations are possible, further tests by controlled experiments are needed to draw firm conclusions.


Zhao, S., Yin, L., Chang, F., Olsen, Søndergaard, M., Jeppesen, E., Li, W. (2016) Response of Vallisneria spinulosa (Hydrocharitaceae) to contrasting nitrogen loadings in controlled lake mesocosms, Hydrobiologia 766, 215–223, http://dx.doi.org/10.1007/s10750-015-2456-1

https://www.researchgate.net/publication/281569455_Response_of_Vallisneria_spinulosa_Hydrocharitaceae_to_contrasting_nitrogen_loadings_in_controlled_lake_mesocosms
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Response of Vallisneria spinulosa (Hydrocharitaceae) to contrasting nitrogen loadings in controlled lake mesocosms

The role of nitrogen (N) in the shift from a macrophyte-dominated state to a phytoplankton-domi- nated one at high N concentrations in shallow lakes is still debated. To elucidate possible toxic and ecological effectsofhighN onmacrophytegrowth,weconducteda short-term (40 day) study of a eutrophication-tolerant macrophyte, Vallisneria spinulosa (Hydrocharitaceae), incubated in pots in a mesocosm system subjected to different N concentrations (1, 3, and 5 mg l - 1 ). Plant leaf and root length as well as growth rate decreased significantly with increased N concentrations, but most N- and P-related physiological parameters, including the soluble protein content, nitrate reductase activity, acid phosphatase activity, and tissue N and P contents, did not differ significantly among the N treatments. Only the alkaline phosphatase activity differed, being lower athighnitrogenloading,likelydue toP limitation. Epiphyton and phytoplankton biomasses increased significantly with increasing N loading. Our results including a large number of physiological tests of the macrophytes, therefore, provide supporting evidence that the loss of submerged macrophytes, like V. spinulosa , seen at high N loading in shallow lakes, can be attributed to competition with phytoplankton and epiphyton rather than to toxic effects.


Zhang, Z., Cao, Y., Jeppesen, E., Li, W. (2016) The response of Vallisneria spinulosa (Hydrocharitaceae) and plankton to pulse addition of inorganic nitrogen with different loading patterns, Hydrobiologia 767, 175–184, http://dx.doi.org/10.1007/s10750-015-2494-8

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The response of Vallisneria spinulosa (Hydrocharitaceae) and plankton to pulse addition of inorganic nitrogen with different loading patterns

The global climate change may lead to more extreme climate events such as severe flooding creating excessive pulse-loading of nutrients, includ- ing nitrogen (N), to freshwaters. We conducted a 3-month mesocosm study to investigate the responses of phytoplankton, zooplankton and Vallisneria spin- ulosa to different N loading patterns using weekly and monthly additions of in total 14 g N m - 2 month - 1 during the first 2 months. The monthly additions led to higher phytoplankton chlorophyll a and total phyto- plankton biomass than at ambient conditions as well as lower leaf biomass and a smaller ramet number of V. spinulosa . Moreover, the biomass of cyanobacteria was higher during summer (August) in the monthly treatments than those with weekly or no additions. However, the biomass of plankton and macrophytes did not differ among the N treatments at the end of the experiment, 1 month after the termination of N addition. We conclude that by stimulating the growth of phytoplankton (cyanobacteria) and reducing the growth of submerged macrophytes, short-term extreme N loading may have significant effects on shallow nutrient-rich lakes and that the lakes may show fast recovery if they are not close to the threshold of a regime shift from a clear to a turbid state. .


Zhang, X., Liua, Z., Jeppesend, E., Taylor, W. D., Rudstam, L. G. (2016) Effects of benthic-feeding common carp and filter-feeding silver carp on benthic-pelagic coupling: Implications for shallow lake management, Ecological Engineering 88, 256–264, http://dx.doi.org/10.1016/j.ecoleng.2015.12.039

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Effects of benthic-feeding common carp and filter-feeding silver carp on benthic-pelagic coupling: Implications for shallow lake management

Benthic–pelagic coupling is a key factor in the dynamics of shallow lakes. A 12-week mesocosm exper-iment was set up to test the hypotheses that benthic-feeding common carp (Cyprinus carpio) reduce the growth of benthic algae and promote eutrophication and that filter-feeding silver carp (Hypoph-thalmichthys molitrix) stimulate benthic algae growth and promote the establishment of a clear-water state. Compared to the controls, the common carp treatment had higher concentrations of total nitrogen (TN) and total phosphorus (TP) in the water column, higher biomass of pelagic algae (measured as chloro-phyll a), higher total suspended solids (TSS) concentrations, lower light intensity, and lower biomass of benthic algae at the sediment surface. Silver carp did not change the chlorophyll a of pelagic algae relative to the controls, but they did decrease the biomass of benthic algae and increase TP and TSS. A microcosm experiment using 32P radiotracer was conducted to examine effects of the two carp species on the release of sediment phosphorus (P). The P release to the water column was higher with common carp present than without common carp. This was not the case in the silver carp experiments. Our findings show that both common carp and silver carp deteriorate water quality by increasing TP and TSS concentrations and decreasing the biomass of benthic algae at the sediment surface. Common carp had a larger negative effect on water quality than silver carp, perhaps because only common carp enhanced P release from the sediment. The implications for lake management are that removal of both common carp and silver carp from shallow lakes may enhance the growth of benthic algae and help promote the establishment of a clear-water state.


Zhang, Y., Su, Y., Liu, Z., Jeppesen, E., Yu, J. & Jin, M. (2016) Geochemical records of anoxic water mass expansion in an oligotrophic alpine lake (Yunnan Province, SW China) in response to climate warming since the 1980s, Holocene 26, 1847-1857, http://dx.doi.org/0.1177/0959683616645948

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Geochemical records of anoxic water mass expansion in an oligotrophic alpine lake (Yunnan Province, SW China) in response to climate warming since the 1980s

In order to elucidate the effect of recent warming, we studied lipid biomarkers and trace elements in a dated sediment core from Lake Heihai, a small, deep, and ultraoligotrophic alpine lake in Yunnan Province (SW China), being only marginally affected by anthropogenic activities. The variation in lipid biomarkers (such as 10-methyl-C16:0 fatty acid (FA), iso-branched C15 (i-C15) and anteiso-branched C15 (ai-C15) FA, and tetrahymanol) suggests a rapid productivity increase in sulfate reducing bacteria and ciliates since 1980, likely reflecting expansion of the hypolimnion anoxia and a prolonged duration of an oxic–anoxic chemocline in the water column. The concentrations of element molybdenum (Mo) in pre-1980 sediments approach the values in average crust. After 1980, the concentration increased, reaching levels approximately sixfold higher than the initial abundances. This likely reflects a high authigenic Mo deposition when the bottom water was more anoxic and enrichment in H2S. The suggested spatial and temporal expansion of the anoxic bottom water since 1980 was probably a response to the regional climate warming, resulting in stronger water column stratification and terrestrial grass inputs to the lake, and thus higher dissolved oxygen (DO) loss in hypolimnion.


Zhao, S., Yin, L., Chang, F., Olsen, Søndergaard, M., Jeppesen, E., Li, W. (2016). Response of Vallisneria spinulosa (Hydrocharitaceae) to contrasting nitrogen loadings in controlled lake mesocosms. Hydrobiologia 766, 215–223, http://dx.doi.org/10.1007/s10750-015-2456-1

Read abstract

Response of Vallisneria spinulosa (Hydrocharitaceae) to contrasting nitrogen loadings in controlled lake mesocosms

The role of nitrogen (N) in the shift from a macrophyte-dominated state to a phytoplankton-dominated one at high N concentrations in shallow lakes is still debated. To elucidate possible toxic and ecological effects of high N on macrophyte growth, we conducted a short-term (40 day) study of a eutrophication-tolerant macrophyte, Vallisneria spinulosa (Hydrocharitaceae), incubated in pots in a mesocosm system subjected to different N concentrations (1, 3, and 5 mg l-1). Plant leaf and root length as well as growth rate decreased significantly with increased N concentrations, but most N-and P-related physiological parameters, including the soluble protein content, nitrate reductase activity, acid phosphatase activity, and tissue N and P contents, did not differ significantly among the N treatments. Only the alkaline phosphatase activity differed, being lower at high nitrogen loading, likely due to P limitation. Epiphyton and phytoplankton biomasses increased significantly with increasing N loading. Our results including a large number of physiological tests of the macrophytes, therefore, provide supporting evidence that the loss of submerged macrophytes, like V. spinulosa, seen at high N loading in shallow lakes, can be attributed to competition with phytoplankton and epiphyton rather than to toxic effects.


Zhou, Y., Jeppesen, E., Li, L., Zhang, Y., Zhang, X., Li, X. (2016) Impacts of Three Gorges Reservoir on the sedimentation regimes in the downstream-linked two largest Chinese freshwater lakes, Scientific Reports 6 (E35396), http://dx.doi.org/10.1038/srep35396

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Impacts of Three Gorges Reservoir on the sedimentation regimes in the downstream-linked two largest Chinese freshwater lakes

We studied the impacts of Three Gorges Reservoir (TGR) on the sedimentation regimes in the downstream-linked two largest Chinese freshwater lakes, Lake Dongting and Lake Poyang. Our results indicate that up to 1.73 × 10⁹ t sediment was retained in TGR from June 2003 to December 2014. This resulted in a 145.9 × 10⁶ t yr⁻¹ decline in the suspended sediment load at Zhicheng and a 16.8 × 10⁶ t yr⁻¹ lower sediment flow from Yangtze River to Lake Dongting, which partially explains the 13.4 × 10⁶ t yr⁻¹ lower sedimentation in Lake Dongting during the post-TGR period. Furthermore, TGR resulted in a 0.5 ± 0.3 m reduction of the multi-year mean water level at the Lake Poyang outlet Hukou, accelerating the suspended sediment export discharge from the lake. The reduced sedimentation in Lake Poyang during the post-TGR period was estimated to 6.3 × 10⁶ t yr⁻¹. We estimate that a monthly mean concentration of sediment flow from TGR below 0.60 kg m⁻³ will lead to erosion in Lake Dongting and Lake Poyang. Better regulation of TGR may extend the life expectancy of the two vanishing large lakes.


Zhou, Y., Jeppesen, E., Zhang, Y., Shi, K., Liu, X., Zhu, G. (2016) Dissolved organic matter fluorescence at wavelength 275/342 nm as a key indicator for detection of point-source contamination in a large Chinese drinking water lake, Chemosphere 144, 503-509, http://dx.doi.org/10.1016/j.chemosphere.2015.09.027

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Dissolved organic matter fluorescence at wavelength 275/342 nm as a key indicator for detection of point-source contamination in a large Chinese drinking water lake

Surface drinking water sources have been threatened globally and there have been few attempts to detect point-source contamination in these waters using chromophoric dissolved organic matter (CDOM) fl uorescence. To determine the optimal wavelength derived from CDOM fl uorescence as an indicator of point-source contamination in drinking waters, a combination of fi eld campaigns in Lake Qiandao and a laboratory wastewater addition experiment was used. Parallel factor (PARAFAC) analysis identi fi ed six components, including three humic-like, two tryptophan-like, and one tyrosine-like component. All metrics showed strong correlation with wastewater addition ( r 2 > 0.90, p < 0.0001). Both the fi eld campaigns and the laboratory contamination experiment revealed that CDOM fl uorescence at 275/ 342 nm was the most responsive wavelength to the point-source contamination in the lake. Our results suggest that pollutants in Lake Qiandao had the highest concentrations in the river mouths of upstream in fl ow tributaries and the single wavelength at 275/342 nm may be adapted for online or in situ fl uo- rescence measurements as an early warning of contamination events. This study demonstrates the po- tential utility of CDOM fl uorescence to monitor water quality in surface drinking water sources.


Zhou, Y., Zhang, Y., Jeppesen, E., Murphy, K. R., Shi, K., Liu, M., Liu, X. & Zhu, G. (2016) Inflow rate-driven changes in the composition and dynamics of chromophoric dissolved organic matter in a large drinking water lake, Water Research 100, 211-221, http://dx.doi.org/10.1016/j.watres.2016.05.021

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Inflow rate-driven changes in the composition and dynamics of chromophoric dissolved organic matter in a large drinking water lake

Drinking water lakes are threatened globally and therefore in need of protection. To date, few studies have been carried out to investigate how the composition and dynamics of chromophoric dissolved organic matter (CDOM) in drinking water lakes are influenced by inflow rate. Such CDOM can lead to unpleasant taste and odor of the water and produce undesirable disinfection byproducts during drinking water treatment. We studied the drinking water Lake Qiandao, China, and found that the concentrations of suspended particulate matter (SPM) in the lake increased significantly with inflow rate (p < 0.001). Similarly, close relationships between inflow rate and the CDOM absorption coefficient at 350 nm a(350) and with terrestrial humic-like fluorescence C3 and a negative relationship between inflow rate and the first principal component (PC1) scores, which, in turn, were negatively related to the concentrations and relative molecular size of CDOM (p < 0.001), i.e. the concentration and molecular size of CDOM entering the lake increased proportionately with inflow rate. Furthermore, stable isotopes (δD and δ18O) were depleted in the upstream river mouth relative to downstream remaining lake regions, substantiating that riverine CDOM entering the lake was probably driven by inflow rate. This was further underpinned by remarkably higher mean chlorophyll-a and in situ measured terrestrial CDOM fluorescence (365/480 nm) and apparent oxygen utilization (AOU), and notably lower mean PC1 and CDOM spectral slope (S275-295) recorded in the upstream river mouth than in the downstream main lake area. Strong negative correlations between inflow rate and a(250):a(365), S275-295, and the spectral slope ratio (SR) implied that CDOM input to the lake in rainy period was dominated by larger organic molecules with a more humic-like character. Rainy period, especially rainstorm events, therefore poses a risk to drinking water safety and requires higher removal efficiency of CDOM during drinking water treatment processes.


Zhou, Y., Zhou, J., Jeppesen, E., Zhang, Y., Qin, B., Shi, K., Tang, X. & Han, X. (2016) Will enhanced turbulence in inland waters result in elevated production of autochthonous dissolved organic matter?, Science of the Total Environment 543, 405–415, http://dx.doi.org/10.1016/j.scitotenv.2015.11.051

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Will enhanced turbulence in inland waters result in elevated production of autochthonous dissolved organic matter?

Biological activity in lakes is strongly influenced by hydrodynamic conditions, not least turbulence intensity; which increases the encounter rate between plankter and nutrient patches. To investigate whether enhanced turbulence in shallow and eutrophic lakes may result in elevated biological production of autochthonous chromophoric dissolved organic matter (CDOM), a combination of field campaigns and mesocosm experiments was used. Parallel factor analysis identified seven components: four protein-like, one microbial humic-like and two terrestrial humic-like components. During our field campaigns, elevated production of autochthonous CDOM was recorded in open water with higher wind speed and wave height than in inner bays, implying that elevated turbulence resulted in increased production of autochthonous CDOM. Confirming the field campaign results, in the mesocosm experiment enhanced turbulence resulted in a remarkably higher microbial humic-like C1 and tryptophan-like C3 (p<0.01), indicating that higher turbulence may have elevated the production of autochthonous CDOM. This is consistent with the significantly higher mean concentrations of chlorophyll-a (Chl-a) and dissolved organic carbon (DOC) and the enhanced phytoplanktonic alkaline phosphatase activity (PAPA) recorded in the experimental turbulence groups than in the control group (p<0.05). The C:N ratio (from 3.34 to 25.72 with a mean of 13.13±4.08) for the mesocosm CDOM samples further suggested their probable autochthonous origin. Our results have implications for the understanding of CDOM cycling in shallow aquatic ecosystems influenced by wind-induced waves, in which the enhanced turbulence associated with extreme weather conditions may be further stimulated by the predicted global climate change.


Zingel, P., Agasild, H., Karus, K., Kangro, K., Tammert, H., Tonno, I., Feldmann, T., Noges, T. (2016). The influence of zooplankton enrichment on the microbial loop in a shallow, eutrophic lake. European Journal of Protistology 52, 22-35, http://dx.doi.org/10.1016/j.ejop.2015.09.004

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The influence of zooplankton enrichment on the microbial loop in a shallow, eutrophic lake

With increasing primary productivity, ciliates may become the most important members of the microbial loop and form a central linkage in the transformation of microbial production to upper trophic levels. How metazooplankters, especially copepods, regulate ciliate community structure in shallow eutrophic waters is not completely clear. We carried out mesocosm experiments with different cyclopoid copepod enrichments in a shallow eutrophic lake to examine the responses of ciliate community structure and abundance to changes in cyclopoid copepod biomass and to detect any cascading effects on bacterioplankton and edible phytoplankton. Our results indicate that an increase in copepod zooplankton biomass favours the development of small-sized bacterivorous ciliates. This effect is unleashed by the decline of predaceous ciliate abundance, which would otherwise graze effectively on the small-sized ciliates. The inverse relationship between crustacean zooplankton and large predaceous ciliates is an important feature adjusting not only the structure of the ciliate community but also the energy transfer between meta- and protozooplankton. Still we could not detect any cascading effects on bacterio- or phytoplankton that would be caused by the structural changes in the ciliate community.

2015

Baho, D., Tavşanoğlu, Ü. N., Šorf, M., Stefanidis, K., Drakare, S., Scharfenberger, U., Agasild, H., Beklioğlu, M., Hejzlar, J., Adrian, R., Papastergiadou, E., Zingel, P., Søndergaard, M., Jeppesen, E. & Angeler, D. (2015) Macroecological Patterns of Resilience Inferred from a Multinational, Synchronized Experiment, Sustainability 7, 1142-1160, http://dx.doi.org/10.3390/su7021142

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Macroecological Patterns of Resilience Inferred from a Multinational, Synchronized Experiment

The likelihood of an ecological system to undergo undesired regime shifts is expected to increase as climate change effects unfold. To understand how regional climate settings can affect resilience; i.e., the ability of an ecosystem to tolerate disturbances without changing its original structure and processes, we used a synchronized mesocosm experiment (representative of shallow lakes) along a latitudinal gradient. We manipulated nutrient concentrations and water levels in a synchronized mesocosm experiment in different climate zones across Europe involving Sweden, Estonia, Germany, the Czech Republic, Turkey and Greece. We assessed attributes of zooplankton communities that might contribute to resilience under different ecological configurations. We assessed four indicator of relative ecological resilience (cross-scale, within-scale structures, aggregation length and gap size) of zooplankton communities, inferred from discontinuity analysis. Similar resilience attributes were found across experimental treatments and countries, except Greece, which experienced severe drought conditions during the experiment. These conditions apparently led to a lower relative resilience in the Greek mesocosms. Our results indicate that zooplankton community resilience in shallow lakes is marginally affected by water level and the studied nutrient range unless extreme drought occurs. In practice, this means that drought mitigation could be especially challenging in semi-arid countries in the future.


Çakiroğlu, A.I, Levi, E.E., Tavşanoğlu, N., Bezirci, S., Erdoğan, Ş., Filiz, N., Andersen, T. J., Davidson, T. A., Jeppesen, E. & Beklioğlu, M.  (2015) Inferring past environmental change of three Turkish shallow lakes from community changes of sub-fossil cladocera, Hydrobiologia (online), http://dx.doi.org/10.1007/s10750-015-2581-x

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Inferring past environmental changes in three Turkish lakes from sub-fossil Cladocera

Cladocerans are increasingly used in palaeolimnological studies as their community composition is sensitive to both anthropogenic and natural forces in lakes. We present the results of a palaeolimnological investigation of three Turkish shallow lakes located in cold dry steppe and semi-dry Mediterranean climatic regions. The aim was to elucidate historical changes in environmental conditions by analysing sub-fossil cladocerans in 210Pb-dated sediment cores. Sub-fossil cladoceran remains from the surface sediment of 40 Turkish lakes were analysed to examine the environmental factors that most correlated with variation in the cladoceran assemblage. Redundancy analysis showed that salinity, macrophyte abundance, fish density, depth and total phosphorus were the most correlated with change in cladoceran assemblage composition with eigenvalues for the first and the second axes being λ 1 = 0.312 and λ 2 = 0.061, respectively. Sedimentary cladoceran assemblages from three cores were placed passively within the framework of the surface sediment ordination. The results reveal a prevalent impact of salinity, fish abundance and water level changes from the past to present. Thus, using cladoceran-based inferences, we traced key environmental changes related to variation in climate change, restoration and water level regulation over the last century.


Cao., Y., Neif, E. M., Li, W., Coppens, J., Filiz, N., Lauridsen, T. L., Davidson, T. A., Søndergaard, M., Jeppesen, E. (2015) Heat wave effects on biomass and vegetative growth of macrophytes after long-term adaptation to different temperatures: a mesocosm study, Climate Research 66, 265-274, http://dx.doi.org/10.3354/cr01352

ResearchGate
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Heat wave effects on biomass and vegetative growth of macrophytes after long-term adaptation to different temperatures: a mesocosm study

Elevated temperatures and extreme climatic events, such as heat waves, can negatively affect submerged macrophytes. Here, we investigated how submerged macrophytes adapted to three different temperatures: 1) ambient, 2) ca. +3 oC and 3) ca. +4.5 oC responded to a heat wave. After ten years of adaptation, the shoots of two species of submerged macrophytes, Elodea canadensis and Potamogeton crispus, were collected from each of the three temperature treatments and transferred to the two heated treatments for one month. Thereafter, the two heated treatments were exposed to a one-month heat wave with an additional 5 oC temperature increase. For P. crispus, total biomass did not differ among the plants adapted to the different temperatures or between the two heated treatments for the whole duration of the experiment. Plants adapted to the highest temperatures, however, produced a larger number of smaller turions before the heat wave and allocated less biomass to elongation before and after the heat wave. As to E. canadensis, the plants adapted to higher temperatures had higher total biomass before and during the heat wave and allocated more biomass to roots and leaves during the heat wave. Most indicators (e.g. length and biomass) of the macrophyte performance measured during the experiment did not differ between the two heated treatments. In summary, after the ten-year adaptation to higher temperatures, the submerged macrophytes showed adaptive changes in growth and asexual reproduction and responded in a complex way to the heat wave depending on species, growth status and adaptation temperature.


Havens, K. E., Pinto-Coelho, R. M., Beklioğlu, M., Christoffersen, K. S., Jeppsen, E., Lauridsen, T. L., Mazumder A., Méthot, G., Pinel Alloul, B., Tavşanoğlu, Ü. N., Erdoğan, Ş., Vijverberg, J. (2015) Temperature effects on body size of feshwater crustacean zooplanktion from Greenland to the tropics, Hydrobiologia 743, 27-35, http://dx.doi.org/10.1007/s10750-014-2000-8

ResearchGate
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Temperature effects on body size of feshwater crustacean zooplanktion from Greenland to the tropics

The body size of zooplankton has many substantive effects on the function of aquatic food webs. A variety of factors may affect size, and earlier studies indicate that water temperature may be a particularly important variable. Here we tested the hypothesis that the body size of cladocerans, cala-noids, and cyclopoids declines with increasing water temperature, a response documented in an earlier study that considered only cladoceran zooplankton. We tested the hypothesis by comparing body size data that were available from prior studies of lakes ranging from 6 to 74 o latitude and encompassing a temperature range of 2–30°C. Cladoceran body size declined with temperature, in a marginally significant manner (P = 0.10). For cyclopoids, the decline was more significant (P = 0.05). In both cases, there was considerably more variation around the regression lines than previously observed; suggesting that other variables such as fish predation played a role in affecting size. Calanoid body size was unrelated to temperature. In contrast with cladocerans and cyclo-poids, perhaps calanoid body size is not metabolically constrained by temperature or is differently affected by changes in fish predation occurring with increasing temperature. The unexpected result for calanoids requires further investigation.


He, H., Zhu, X., Song, X., Jeppesen, E., Liu, Z. (2015) Phytoplankton response to winter warming modified by large-bodied zooplankton: an experimental microcosm study, Journal of Limnology, http://dx.doi.org/10.4081/jlimnol.2015.1066

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Phytoplankton response to winter warming modified by large-bodied zooplankton: an experimental microcosm study

While several field investigations have demonstrated significant effects of cool season (winter or spring) warming on phytoplankton development, the role played by large-bodied zooplankton grazers for the responses of phytoplankton to winter warming is ambiguous. We conducted an outdoor experiment to compare the effect of winter warming (heating by 3°C) in combination with presence and absence of Daphnia grazing (D. similis) on phytoplankton standing crops and community structure under eutrophic conditions. When Daphnia were absent, warming was associated with significant increases in phytoplankton biomass and cyanobacterial dominance. In contrast, when Daphnia were present, warming effects on phytoplankton dynamics were offset by warming-enhanced grazing, resulting in no significant change in biomass or taxonomic dominance. These results emphasize that large-bodied zooplankton like Daphnia spp. may play an important role in modulating the interactions between climate warming and phytoplankton dynamics in nutrient rich lake ecosystems.


Hering, D., Carvalho, L., Argillier, C., Beklioglu, M., Borja, A., Cardoso, A. C., Duel, H., Ferreira, T., Globevnik, L., Hanganu, J., Hellsten, S., Jeppesen, E., Kodeš, V., Lyche Solheim, A., Nõges, T., Ormerod, S., Panagopoulos, Y., Schmutz, S. Venohr, M., Birk, S. (2015) Managing aquatic ecosystems and water resources under multiple stress - an introduction to the MARS project, Science of The Total Environment 503-504, 10-21, http://dx.doi.org/10.1016/j.scitotenv.2014.06.106

ResearchGate
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Managing aquatic ecosystems and water resources under multiple stress — An introduction to the MARS project

Water resources globally are affected by a complex mixture of stressors resulting from a range of drivers, including urban and agricultural land use, hydropower generation and climate change. Understanding how stressors interfere and impact upon ecological status and ecosystem services is essential for developing effective River Basin Management Plans and shaping future environmental policy. This paper details the nature of these problems for Europe's water resources and the need to find solutions at a range of spatial scales. In terms of the latter, we describe the aims and approaches of the EU-funded project MARS (Managing Aquatic ecosystems and water Resources under multiple Stress) and the conceptual and analytical framework that it is adopting to provide this knowledge, understanding and tools needed to address multiple stressors. MARS is operating at three scales: At the water body scale, the mechanistic understanding of stressor interactions and their impact upon water resources, ecological status and ecosystem services will be examined through multi-factorial experiments and the analysis of long time-series. At the river basin scale, modelling and empirical approaches will be adopted to characterise relationships between multiple stressors and ecological responses, functions, services and water resources. The effects of future land use and mitigation scenarios in 16 European river basins will be assessed. At the European scale, large-scale spatial analysis will be carried out to identify the relationships amongst stress intensity, ecological status and service provision, with a special focus on large transboundary rivers, lakes and fish. The project will support managers and policy makers in the practical implementation of the Water Framework Directive (WFD), of related legislation and of the Blueprint to Safeguard Europe's Water Resources by advising the 3rd River Basin Management Planning cycle, the revision of the WFD and by developing new tools for diagnosing and predicting multiple stressors.


Jeppesen, E., Brucet, S., Naselli-Flores, L., Papastergiadou, E., Stefanidis, K., Nõges, T., Nõges, P., Attayde, J. L., Zohary, T., Coppens, J., Bucak, T., Fernandes Menezes, R., Sousa Freitas, F. R., Kernan, M., Søndergaard, M., Beklioğlu, M. (2015) Ecological impacts of global warming and water abstraction on lakes and reservoirs due to changes in water level and related changes in salinity, Hydrobiologia 750, 201-227, http://dx.doi.org/10.1007/s10750-014-2169-x

ResearchGate
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Ecological impacts of global warming and water abstraction on lakes and reservoirs due to changes in water level and related changes in salinitys

According to the Intergovernmental Panel on Climate Change report released in September 2014, unprecedented changes in temperature and precipitation patterns have been recorded globally in recent decades and further change is predicted to occur in the near future, mainly as the result of human activity. In particular, projections show that the Mediterranean climate zone will be markedly affected with significant implications for lake water levels and salinity. This may be exacerbated by increased demands for irrigation water. Based on long-term data from seven lakes and reservoirs covering a geographical gradient of 52° of latitudes and a literature review, we discuss how changes in water level and salinity related to climate change and water abstraction affect the ecosystem structure, function, biodiversity and ecological state of lakes and reservoirs. We discuss mitigation measures to counteract the negative effects on ecological status that are likely to result from changes in climate and water abstraction practices. Finally, we highlight research required to improve knowledge of the impacts of anthropogenically induced changes on lake water level and consequent changes in salinity.


Kattel, G., Gell, P., Perga, M.-E., Jeppesen, E., Grundell, R., Weller S., Zawadzki, A., Barry, L. (2015) Tracking a century of change in trophic structure and dynamics in a floodplain wetland: integrating palaeoecological and palaeoisotopic evidence, Freshwater Biology 60, 711–723 , http://dx.doi.org/10.1111/fwb.12521

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Tracking a century of change in trophic structure and dynamics in a floodplain wetland: integrating palaeoecological and palaeoisotopic evidence

The palaeoecological assessment, and the use of stable isotopes of carbon in subfossils of herbivores and omnivores, represents a novel approach to understand transitions in past food-web structure and the dynamics of lake ecosystems in response to natural perturbations and human impacts. Combined with records of subfossil assemblages of cladocerans and chironomids, it may be possible to decipher whether changes are attributable to external forces or internally derived system shifts.A sediment record taken from the shallow (2.3 m depth) Kings Billabong in the River Murray floodplain (Australia) was analysed to explore changes in trophic dynamics over the past century.The palaeoecological assessment revealed that littoral assemblages of cladocerans and benthic diatoms were gradually replaced by planktonic (planktonic and facultative planktonic) assemblages after river regulation in the 1920s.The stable isotopic composition of carbon (δ13C), derived from chironomid head capsules, was relatively constant down-core, ranging between −26.1‰ and −24.0‰, and coincided largely with the δ13C of bulk sediment samples (−25.6‰ to −22.0‰). The δ13C values of pelagic (Daphnia) and ubiquitous (Bosmina, Alona) cladocerans, however, varied markedly, with that for Daphnia between −29.8‰ (10–20 cm) and −23.2‰ (60–70 cm), and for ubiquitous cladocerans, between −29.4‰ (20–30 cm) and −24.5‰ (80–70 cm).The temporal changes in the δ13C values of cladocerans also suggest a gradual transition from a macrophyte-dominated state to a phytoplankton-dominated state after river regulation and further indicate changes in the horizontal migration behaviour of Daphnia depending on macrophyte abundance and predation risk.Our study demonstrates the potential of reconstructing, more precisely, the trophic dynamics of large river floodplain lakes and their ecological resilience by combining subfossil analyses with stable isotope analyses of selected subfossil groups.


Levi, P. S., Riis, T., Alnøe, A. B., Peipoch, M., Maetzke, K., Bruus, C. & Baattrup-Pedersen, A. (2015) Macrophyte Complexity Controls Nutrient Uptake in Lowland Streams, Ecosystems Ecosystems 18, 914–931, http://dx.doi.org/10.1007/s10021-015-9872-y

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Macrophyte Complexity Controls Nutrient Uptake in Lowland Streams

Macrophytes act as ecosystem engineers in lowland stream ecosystems, enhancing habitat complexity and physical structure. Studies have demonstrated that macrophyte abundance and growth form can dictate the degree to which physical and biological stream characteristics are altered. However, few studies have investigated the influence of macrophytes and their species-specific variation in morphological complexity on functional processes, such as nutrient uptake. We injected 15N-labeled ammonium (15N-NH4 +) into four macrophyte-rich lowland streams in Denmark to quantify the uptake of NH4 + by macrophytes, epiphytic biofilms, benthic biofilms, and suspended particulate organic matter in the water column. Overall, macrophytes and their epiphytic biofilms accounted for 71-98% of the reach-weighted uptake across the study streams. While macrophytes had the highest rates of NH4 + uptake among the compartments we measured, the epiphytic biofilms had the highest uptake efficiency, ranging from 0.06 to 0.6 mg N mg N biomass −1 d−1. Among all compartments, the uptake efficiency was inversely related to the carbon-to-nitrogen ratio. Macrophyte complexity, expressed as leaf perimeter-to-area ratio (P:A), varied among the five species found in the study streams. The uptake rates by macrophyte species with high leaf P:A were, on average, an order of magnitude higher than the rates for species with simple leaf morphology (430 vs. 49 mg N m−2 d−1). In summary, our results indicate that macrophytes regulate stream function both via direct uptake of NH4 + from the water column and by providing a substrate for epiphytic biofilms. Furthermore, the effect of leaf architecture on nutrient uptake rates provides evidence that physical complexity can enhance ecosystem function.


Mahdy A., Hilt, S., Filiz, N., Beklioğlu, M., Hejzlar, J., Özkundakci, D., Papastergiadou, E., Scharfenberger, U., Šorf, M., Stefanidis, K., Tuvikene, L., Zingel, P., Søndergaard, M., Jeppesen, E., Adrian, R. (2015) Effects of water temperature on summer periphyton biomass in shallow lakes: a pan-European mesocosm experiment, Aquatic Sciences 77, 499-510, http://dx.doi.org/10.1007/s00027-015-0394-7

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Effects of water temperature on summer periphyton biomass in shallow lakes: a pan-European mesocosm experiment

Periphyton communities play an important role in shallow lakes and are controlled by direct forces such as temperature, light, nutrients, and invertebrate grazing, but also indirectly by planktivorous fish predation. We performed a pan-European lake mesocosm experiment on periphyton colonization covering five countries along a north/south geographical/temperature gradient (Estonia, Germany, Czech Republic, Turkey, and Greece). Periphyton biomass on artificial polypropylene strips exposed at 50 cm water depth at low and high nutrient regimes (with mean total phosphorus concentration of 20 and 65 µg L−1, respectively) was compared during mid-summer. No significant effect of nutrient loading on periphyton biomass was observed as nutrient concentrations in the mesocosms were generally above limiting values. Water temperature significantly enhanced summer periphyton biomass development. Additionally, direct and indirect top-down control of snails and fish emerged as a significant factor in periphyton biomass control.


Nõges, P., Argillier, C., Borja, Á., Garmendia J. M., Hanganu, J., Kodeš, V., Pletterbauer, F., Sagouis, A., Birk S. (2015) Quantified biotic and abiotic responses to multiple stress in freshwater, marine and ground waters, Science of The Total Environment, http://dx.doi.org/10.1016/j.scitotenv.2015.06.045

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Quantified biotic and abiotic responses to multiple stress in freshwater, marine and ground waters

We reviewed 219 papers and built an inventory of 532 items of ecological evidence on multiple stressor impacts in rivers, lakes, transitional and coastal waters, as well as groundwaters. Our review revealed that, despite the existence of a huge conceptual knowledge base in aquatic ecology, few studies actually provide quantitative evidence on multi-stress effects. Nutrient stress was involved in 71% to 98% of multi-stress situations in the three types of surface water environments, and in 42% of those in groundwaters. However, their impact manifested differently along the groundwater-river-lake-transitional-coastal continuum, mainly determined by the different hydro-morphological features of these ecosystems. The reviewed papers addressed two-stressor combinations most frequently (42%), corresponding with the actual status-quo of pressures acting on European surface waters as reported by the Member States in the WISE WFD Database (EEA, 2015). Across all biological groups analysed, higher explanatory power of the stress-effect models was discernible for lakes under multi-stressor compared to single stressor conditions, but generally lower for coastal and transitional waters. Across all aquatic environments, the explanatory power of stress-effect models for fish increased when multi-stressor conditions were taken into account in the analysis, qualifying this organism group as a useful indicator of multi-stress effects. In contrast, the explanatory power of models using benthic flora decreased under conditions of multiple stress.


Olsen, S., Jeppesen, E., Moss, B., Ozkan, K., Beklioglu, M., Feuchtmayr, H., González Sagrario, M., Li, W., Larsen, S.E., Søndergaard, M. (2015) Factors influencing nitrogen processing in lakes: an experimental approach, Freshwat. Biol. 60, 642-662, http://dx.doi.org/10.1111/fwb.12511

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Factors influencing nitrogen processing in lakes: an experimental approach

  1. To help improve our understanding of the nitrogen cycle in lakes, particularly in the context of climate change, we analysed total nitrogen (TN) and nitrate (inline image-N) data from six mesocosm experiments (in Denmark, U.K., China and Turkey) covering different climatic regions. We assessed the effects of nitrogen (N) and phosphorus (P) loading, temperature, salinity and water level on N processing.
  2. Water column N loss (defined as the nitrogen processed in and lost from the water column in units of net amount processed per unit area and per unit of time, or in relative terms as the percentage loss of the total pool in 2 weeks) was particularly sensitive to external nutrient loading to the mesocosms. Mean water column TN loss at high N loading varied from 111 to 250 mg m−2 day−1 and increased with N loading. High P loading resulted in increased water column N loss, possibly because of increased uptake into plants and attached algae and sedimentation of the increased algal crop. High salinity generally decreased water column TN loss; on average, 10% more TN was in the water column at 12‰ salinity than at 2‰ salinity, while no significant effect of water level was found.
  3. Only weak relationships were observed between N processing and temperature, and mesocosms limited by P accumulated more nitrogen in their water columns than those with high P loadings. Our results suggest that N processing in lakes appears to be more sensitive to features of the catchment, such as hydrology and loading, than to climatic effects related to temperature, salinity and water level.

Ren, L., Jeppesen, E., He, D., Wang, J., Liboriussen, L., Xing, P., Wu, Q. L. (2015) Influences the Importance of Niche-Related and Neutral Processes in Lacustrine Bacterioplankton Assembly, Applied and Environmental Microbiology, http://dx.doi.org/10.1128/AEM.04042-14

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Influences the Importance of Niche-Related and Neutral Processes in Lacustrine Bacterioplankton Assembly

pH is an important factor that shapes the structure of bacterial communities. However, we have very limited information about the patterns and processes by which overall bacterioplankton communities assemble across wide pH gradients in natural freshwater lakes. Here, we used pyrosequencing to analyze the bacterioplankton communities in 25 discrete freshwater lakes in Denmark with pH levels ranging from 3.8 to 8.8. We found that pH was the key factor in impacting lacustrine bacterioplankton community assembly. More acidic lakes imposed stronger environmental filtering, which decreased the richness and evenness of bacterioplankton operational taxonomic unit (OTU) and largely shifted community composition. Although environmental filtering was detected to be the most important determinant of bacterioplankton community assembly, the importance of neutral assembly processes must also be considered notably in acidic lakes, where the species (OTU) diversity was low. We observed that the strong effect of environmental filtering in more acidic lakes was weakened by the enhanced relative importance of neutral community assembly, and bacterioplankton communities tended to be less phylogenetically clustered in more acidic lakes. In summary, we propose that pH was a major environmental determinant in freshwater lakes, regulating the relative importance and interplay between niche-related and neutral processes and shaping the patterns of freshwater lake bacterioplankton biodiversity.


Schmidt-Kloiber, A. & D. Hering (2015) www.freshwaterecology.info – An online tool that unifies, standardises and codifies more than 20,000 European freshwater organisms and their ecological preferences, Ecological Indicators 53, 271–282, dx.doi.org/10.1016/j.ecolind.2015.02.007

www.freshwaterecology.info

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www.freshwaterecology.info – An online tool that unifies, standardises and codifies more than 20,000 European freshwater organisms and their ecological preferences

Species’ ecological preferences are progressively important for understanding distribution patterns, for conserving biodiversity or for assessing and evaluating the status of freshwater ecosystems. Comprehensive databases compiling species traits are already established in the terrestrial realm, but widely missing in freshwater science. We established a database for European taxa of five aquatic organism groups by compiling information on taxonomy, ecology and distribution based on extensive literature surveys, which were performed by experts for the targeted organism groups. The database includes fishes (654 taxa/21 ecological preferences), macro-invertebrates (8586/40), macrophytes (1083/5), diatoms (8868/36) and phytoplankton (1976/4). It is available online with various options and tools for finding information and has currently over 800 users. The reviewed literature as well as examples given in this paper, highlight the importance of the general availability of knowledge on ecological preferences for various aspects in ecological assessment. Freshwaterecology.info is considered a service for basic research, applied scientists, water managers or other stakeholders. It serves as base for bioassessment and monitoring.


Šorf, M., Davidson, T. A., Brucet,  S., Menezes, R. F., Søndergaard, M., Lauridsen, T. L., Landkildehus, F., Liboriussen, L.,  Jeppesen, E. (2015) Zooplankton response to climate warming: a mesocosm experiment at contrasting temperatures and eutrophication states, Hydrobiologia 742, 185-203, http://dx.doi.org/10.1007/s10750-014-1985-3

ResearchGate
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Zooplankton response to climate warming: a mesocosm experiment at contrasting temperatures and nutrient levels

Zooplankton community response to the combined effects of nutrients and fish (hereafter N-F) at contrasting temperatures was studied in a long-term experiment conducted in 24 shallow lake mesocosms with low and high nutrient levels. We found a positive effect of N-F on zooplankton biomass, chlorophyll-a and turbidity. In contrast, zooplankton species and size diversity decreased with added N-F, as did submerged macrophyte plant volume inhabited (PVI). The community composition of zooplankton in high N-F mesocosms was related to chlorophyll-a and turbidity and to macrophyte PVI in the low N ? F mesocosms. Macrophytes can protect zooplankton from fish predation. Compared to N ? F effects, temperature appeared to have little effect on the zooplankton community. Yet analysis of community heterogeneity among treatments indicated a significant temperature effect at high N-F levels. The results indicate an indirect temperature effect at high N-F levels that can be attributed to tempera-ture-dependent variation in fish density and/or chlorophyll-a concentration.


Tavşanoğlu, Ü. N., Brucet, S., Levi E. E., Bucak, T., Bezirci, G., Özen, A., Johansson, L. S., Jeppesen, E., Beklioğlu, M. (2015) Size-based diel migration of zooplankton in Mediterranean shallow lakes assessed from in situ experiments with artificial plants, Hydrobiologia online, http://dx.doi.org/10.1007/s10750-015-2192-6

ResearchGate
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Size-based diel migration of zooplankton in Mediterranean shallow lakes assessed from in situ experiments with artificial plants

In warm lakes, fish aggregate within macrophytes, thereby weakening the role of these as a daytime refuge for zooplankton and altering the zooplankton size structure, predation pressure, and water clarity. To elucidate the role of macrophytes as a refuge for zooplankton and their effect on zooplankton size distribution, we established three sets of strandardized artificial plant beds in 11 lakes in Turkey with contrasting fish predation risk and turbidity. Zooplankton were sampled within and outside of each plant beds during day and night. Fish, collected overnight in multimesh-sized gillnets, were abundant both inside and outside the artificial plant beds, impoverishing the usefulness of plants as a daytime refuge for particularly large-bodied zooplankton. Zooplankton size diversity was negatively related to fish abundance. Diel vertical migration was the frequent anti-predator avoidance behavior, but reverse migration was also observed when Chaoborus was present. In contrast to the small-bodied taxa, large- and medium-sized taxa showed intraspecific size-based migration (i.e., individuals of different sizes had different migration patterns). Predators influenced the size structure and diel movement of zooplankton, but the response changed with the size of zooplankton and water clarity.


Teixeira-de Mello, F., Meerhoff, M., González-Bergonzoni, I., Kristensen, E. A., Baattrup-Pedersen, A., Jeppesen, E. (2015) Influence of riparian forests on fish assemblages in temperate lowland streams, Environmental Biology of Fishes 99, 133-144, http://dx.doi.org/10.1007/s10641-015-0462-9

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Influence of riparian forests on fish assemblages in temperate lowland streams

The characteristics of riparian vegetation along streams vary with natural and anthropogenic factors. Deforestation for agricultural purposes has consequences for the physical in-stream structure and function, such as the predominance of autotrophic or heterotrophic stream metabolism. Open canopy lowland streams are often dominated by macrophytes, with potential direct and indirect effects on the fish community. We tested for possible differences in the structure (relative abundance of species, mean body size, and density) and composition (species richness, species identity, and different trophic groups) of fish assemblages between open canopy streams (OCS) and riparian forest streams (RFS), including pool and riffle habitats, in temperate lowland Denmark. OCS reaches exhibited higher alpha and beta diversity and frequently hosted rare species. Almost 50 % of the recorded species appeared only in OCS. OCS also had smaller mean body size of fish and tended to have higher fish densities. The relative abundance of the different trophic groups did not differ between the two streams types, but the RFS had a higher abundance and occurrence frequency of intolerant salmonids. Our results suggest that modification of riparian habitats can affect richness patterns and that strong functional changes may occur as a consequence of forest clearance through changes in the relative importance of a keystone species, trout (Salmo trutta).


Trolle, D., Nielsen, A., Rolighed, J., Thodsen, H., Andersen, H. E., Karlsson, I. B., Refsgaard, J. C., Olesen, J. E., Bolding, K., Kronvang, B., Søndergaard, M., Jeppesen, E. (2015) Projectin the future ecological state of lakes in Denmark in a 6 degree warmin scenario, Climate Research 64, 55-72, http://dx.doi.org/10.3354/cr01278

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Projecting the future ecological state of lakes in Denmark in a 6 degree warming scenario

Lakes are highly sensitive to climate change, and climate warming is known to induce eutrophication symptoms in temperate lakes. In Denmark, climate is projected to cause increased precipitation in winter and increased air temperatures throughout the year by the end of the 21st century. Looking further into the future, the warming trend is projected to continue and likely reach a 6°C increase around the 22nd century (relative to a baseline period of 1986-2005). In the present study, we evaluate the consequences of such extreme changes for temperate Danish lakes. We use a multifaceted modelling approach by combining an eco-hydrological model to estimate future water runoff and catchment nutrient exports with both mechanistic and empirical lake models, describing key biogeochemical indicators in lakes, in order to quantify the effects of future nutrient loads and air temperature on lake ecosystems. Our model projections for the future scenario suggest that annual water runoff will increase (46%), driving also increases in exports of nitrogen and phosphorus (13 and 64%, respectively). Both the mechanistic and empirical modelling approaches suggest that phytoplankton biomass will increase and that potentially toxin-producing cyanobacteria may become a dominant feature of the phytoplankton community from spring. Warming and increased nutrient loads also affect the food webs within the lakes in the direction of higher fish control of algae-grazing water fleas, further reinforcing eutrophication. To be able to mitigate these eutrophication effects, external nutrient loading to the lakes must be reduced considerably.


Weyhenmeyer, G. A., Kosten, S., Wallin, M. B., Tranvik, L. J., Jeppesen, E., & Roland, F. (2015) Significant fraction of CO2 emissions from boreal lakes derived from hydrologic inorganic carbon inputs, Nature Geoscience, advance online publication.

Read also the related Freshwater blog post

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Annual CO2 emissions from lakes and other inland waters into the atmosphere are estimated to almost entirely compensate the total annual carbon uptake by oceans1, 2, 3. CO2 supersaturation in lakes, which results in CO2 emissions, is frequently attributed to CO2 produced within the lake4, 5, 6, 7, 8. However, lateral inorganic carbon flux through watersheds can also be sizeable9, 10, 11. Here we calculated lake surface water CO2 concentrations and emissions using lake pH, alkalinity and temperature from a compilation of data from 5118 boreal lakes12. Autumn surface water CO2 concentrations and CO2 emissions from the 5118 lakes co-varied with lake internal autumn CO2 production. However, using a mass balance approach we found that CO2 emission in the majority of lakes was sustained by inorganic carbon loading from the catchment rather than by internal CO2 production. Small lakes with high dissolved organic carbon and phosphorus concentrations, shorter retention times and longer ice-free seasons had the highest CO2 concentrations. CO2 emissions from these small lakes was twice that of comparable lakes in colder regions, and similar to emissions from subtropical and tropical lakes. We conclude that changes in land use and climate that increase dissolved inorganic carbon may cause emission levels from boreal lakes to approach those of lakes in warmer regions.


Yu, Q., Wang, H.-J., Li, Y., Shao, J.-C., Liang, X.-M., Jeppesen, E., Wang, H.-J. (2015) Effects of high nitrogen concentrations on the growth of submersed macrophytes at moderate phosphorus concentrations, Water Research 83, 385-395, http://dx.doi.org/10.1016/j.watres.2015.06.053

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Effects of high nitrogen concentrations on the growth of submersed macrophytes at moderate phosphorus concentrations

Eutrophication of lakes leading to loss of submersed macrophytes and higher turbidity is a worldwide phenomenon, attributed to excessive loading of phosphorus (P). However, recently, the role of nitrogen (N) for macrophyte recession has received increasing attention. Due to the close relationship between N and P loading, disentanglement of the specific effects of these two nutrients is often difficult, and some controversy still exists as to the effects of N. We studied the effects of N on submersed macrophytes represented by Vallisneria natans (Lour.) Hara in pots positioned at three depths (0.4 m, 0.8 m, and 1.2 m to form a gradient of underwater light conditions) in 10 large ponds having moderate concentrations of P (TP 0.03 ± 0.04 mg L_1) and five targeted concentrations of total nitrogen (TN) (0.5, 2, 10, 20, and 100 mg L_1), there were two ponds for each treatment. To study the potential shading effects of other primary producers, we also measured the biomass of phytoplankton (ChlaPhyt) and periphyton (ChlaPeri) expressed as chlorophyll a.We found that leaf length, leaf mass, and root length of macrophytes declined with increasing concentrations of TN and ammonium, while shoot number and root mass did not. All the measured growth indices of macrophytes declined significantly with ChlaPhyt, while none were significantly related to ChlaPeri. Neither ChlaPhyt nor ChlaPeri were, however, significantly negatively related to the various N concentrations. Our results indicate that shading by phytoplankton unrelated to the variation in N loading and perhaps toxic stress exerted by high nitrogen were responsible for the decline in macrophyte growth.


Zhang, X., Odgaard, R., Olesen, B., Lauridsen, T. L., Liboriussen, L., Søndergaard, M., Liu, Z. & Jeppesen, E. (2015) Warming shows differential effects on late-season growth and competitive capacity of Elodea canadensis and Potamogeton crispus in shallow lakes, Inland Waters 5, 421-432, http://dx.doi.org/10.5268/IW-5.4.830

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Warming shows differential effects on late-season growth and competitive capacity of Elodea canadensis and Potamogeton crispus in shallow lakes

Submerged macrophytes are likely to be affected by climate changes through changes in water temperatures and length of growing season. We conducted a lab experiment to examine the influence of a late-season temperature increase on growth, biomass allocation, and acclimation of 2 submerged macrophyte species, Elodea canadensis and Potamogeton crispus. We also ran competitive interaction experiments between the 2 species with mono- and mixed-species cultures in pots placed in outdoor heated mesocosms (5 years at ambient temperature and a higher temperature following the IPCC A2 scenario downscaled to local conditions but enhanced by 50%). In the lab, macrophytes collected in the 2 types of mesocosms were grown at ambient temperatures (12 °C in September and 8 °C in October) and 4 °C higher. Warming had an overall stronger effect on E. candensis than P. crispus, particularly within the low temperature range studied. Hence, the relative growth rate (RGR) of E. canadensis acclimated to ambient mesocosm conditions increased 6-fold from low (8 °C) to high (16 °C) temperature, whereas the RGR of P. crispus increased


Zhou, Y., Jeppesen, E., Zhang, Y., Niu, C., Shi, K., Liu, X., Zhu, G., Qin, B. (2015) Chromophoric dissolved organic matter of black waters in a highly eutrophic Chinese lake: Freshly produced from algal scums?, Journal of Hazardous Materials 299, 222–230, http://dx.doi.org/10.1016/j.jhazmat.2015.06.024

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Chromophoric dissolved organic matter of black waters in a highly eutrophic Chinese lake: Freshly produced from algal scums?

Field campaigns and an incubation experiment were conducted to evaluate the sources of chromophoric dissolved organic matter (CDOM) in black water spots in highly polluted regions of the Chinese Lake Taihu. A significant positive correlation (< 0.0001) was found between chlorophyll a (Chl-a) and the CDOM absorption coefficient a(350), indicating that algae degradation was likely the primary source of CDOM in black waters. This is supported by our field results that Chl-a, a(350) and the spectral slope ratio (SR) were significantly higher in the black water samples than in the regular samples (< 0.001). Our incubation experiment further substantiated the primary significance of biological CDOM source where a(350) increased with decreasing Chl-a concentrations. After seven days’ incubation, a 72.2% decrease and a 74.9% increase were recorded for Chl-a and a(350), respectively, relative to the initial values. Parallel factor analysis identified five fluorescent components. The maximal fluorescence intensity (Fmax) of tryptophan-like C1 and microbial humic-like C3 of black water samples was significantly higher than in the regular water samples (< 0.0005). This is consistent with incubation experiment results showing a rapid increase in Fmax of the two components, emphasizing the priority of the in situ biological CDOM source in black water spots.


Ziegler, C. R., Webb, J. A., Norton, S. B., Pullin, A. S., Melcher, A. H. (2015)Digital repository of associations between environmental variables: A new resource to facilitate knowledge synthesis, Ecological Indicators 53, 61-69, http://dx.doi.org/10.1016/j.ecolind.2015.01.003

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Digital repository of associations between environmental variables: A new resource to facilitate knowledge synthesis

Responsible care and management of Earth's resources requires scientific support, but the pool of underused research is growing rapidly. Environmental science research studies describe associations between variables (e.g. statistical relationships between stressors and responses). We propose open-access and online sharing of such associations. This concept differs from various efforts around the world to promote sharing of primary research data, but holds similar goals of improved use of existing knowledge. The initiative is made possible by recent developments in information technology and evolving online culture (e.g. crowdsourcing and citizen science). We have begun to connect existing projects that catalog and store associations, thereby moving toward a single virtual repository. Researchers and decision makers may share and re-use associations for myriad purposes, including: increasing efficiency and timeliness of systematic reviews, environmental assessments and meta-analyses, identifying knowledge gaps and research opportunities, providing evolved metrics of research impact, and demonstrating connections between research and environmental improvement.


2014

Birk, S., Ecke, F. (2014) The potential of remote sensing in ecological status assessment of coloured lakes using aquatic plants, Ecological Indicators 46, 398-406, http://dx.doi.org/10.1016/j.ecolind.2014.06.035

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The potential of remote sensing in ecological status assessment of coloured lakes using aquatic plants

Field-based survey methods for aquatic vegetation have been identified as resource-demanding. Recent advances in remote sensing (RS) with sub-decimetre resolution allow for surveying aquatic vegetation at the species level. Coloured lakes, mainly due to high concentrations of humic substances, are globally widespread. However, high colour impedes the identification of submerged vegetation via remote sensing. Here, we evaluate the potential of using only emergent, floating and floating-leaved taxa that are detectable by high-resolution RS (RS-taxa) to assess the ecological status of lakes. In a dataset covering 72 Swedish low alkaline coloured lakes, we identified 31 RS-taxa. The power of RS-taxa assemblages to predict non-RS assemblages was analysed by a combination of ordination (Detrended Correspondence Analysis, DCA, and Redundancy Analysis) and multiple regression analysis. We compared the performance of a trophic metric score based on RS-taxa with that based on field data from all taxa along different environmental gradients. Forty percent of the variability of the first non-RS taxa DCA-axis was predicted by the DCA-results based on RS-taxa. Correlations of the trophic metric score and total nitrogen concentrations were equally strong for the dataset based on RS-taxa compared to the dataset based on all taxa. For total phosphorous concentrations, the correlation was stronger for the dataset based on all taxa, but for a complex water quality gradient (including sulphate, N-species, chlorophyll and percent cover of wetlands in the riparian buffer) the correlation was higher for the RS-taxa dataset. The significant linkage between the two community fractions (remotely-sensible and non-sensible) revealed considerable assemblage concordance, suggesting a notable potential of the use of remote sensing in lake macrophyte monitoring. The established trophic metric score seems most qualified for surveillance monitoring that, in combination with the eased efforts of data acquisition, detects long-term changes of the aquatic environment caused by shifts in climate, land use and (related) eutrophication.


Çakıroğlu, A.I., Tavşanoğlu, Ü. N., Davidson,T. A., Levi, E. E., Bucak, T., Özen, A., Akyıldız, G. K., Jeppesen, E., Beklioğlu, M.(2014). Relatedness between contemporary and surface sediment subfossil cladocera assemblages in Turkish shallow lakes, Paleolim 52, 367-383, http://dx.doi.org/10.1007/s10933-014-9799-x

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Relatedness between contemporary and subfossil cladoceran assemblages in Turkish lakes

Cladocerans are valuable indicators of environmental change in lakes. Their fossils provide information on past changes in lake environments. However, few studies have quantitatively examined the relationships between contemporary and sub-fossil cladoceran assemblages and no investigations are available from Mediterranean lakes where salinity, eutrophication and top-down control of large-bodied cladocerans are known to be important. Here we compared contemporary Cladocera assemblages, sampled in summer, from both littoral and pelagic zones, with their sub-fossil remains from surface sediment samples from 40 Turkish, mainly shallow, lakes. A total of 20 and 27 taxa were recorded in the contemporary and surface sediment samples, respectively. Procrustes rotation was applied to both the principal components analysis (PCA) and redundancy analysis (RDA) ordinations in order to explore the relationship between the cladoceran community and the environmental variables. Procrustes rotation analysis based on PCA showed a significant accord between both littoral and combined pelagic–littoral contemporary and sedimentary assemblages. RDA ordinations indicated that a similar proportion of variance was explained by environmental variation for the contemporary and fossil Cladocera data. Total phosphorus and salinity were significant explanatory variables for the contemporary assemblage, whereas salinity emerged as the only significant variable for the sedimentary assemblage. The residuals from the Procrustes rotation identified a number of lakes with a high degree of dissimilarity between modern and sub-fossil assemblages. Analysis showed that high salinity, deep water and high macrophyte abundance were linked to a lower accord between contemporary and sedimentary assemblages. This low accord was, generally the result of poor representation of some salinity tolerant, pelagic and macrophyte-associated taxa in the contemporary samples. This study provides further confirmation that there is a robust relationship between samples of modern cladoceran assemblages and their sedimentary remains. Thus, sub-fossil cladoceran assemblages from sediment cores can be used with confidence to track long-term changes in this environmentally sensitive group and in Mediterranean lakes, subjected to large inter-annual variation in water level, salinity and nutrients.


Cao Y., Li, W., Jeppesen, E. (2014) The response of two submerged macrophyte and periphyton to elevated temperature at high nutrient level: a microcosm approach, Hydrobiologia 738, 49–59, http://dx.doi.org/10.1007/s10750-014-1914-5

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The response of two submerged macrophytes and periphyton to elevated temperatures in the presence and absence of snails: a microcosm approach

Global warming may affect snail–periphyton–macrophyte relationships in lakes with implications also for water clarity. We conducted a 40-day aquaria experiment to elucidate the response of submerged macrophytes and periphyton on real and artificial plants to elevated temperatures (3°C) under eutrophic conditions, with and without snails present. With snails, the biomass and length of Vallisneria spinulosa leaves increased more at the high temperature, and at both temperatures growth was higher than in absence of snails. The biomass of periphyton on V. spinulosa as well as on artificial plants was higher at the highest temperature in the absence but not in the presence of snails. The biomass of Potamogeton crispus (in a decaying state) declined in all treatments and was not affected by temperature or snails. While total snail biomass did not differ between temperatures, lower abundance of adults (size >1 cm) was observed at the high temperatures. We conclude that the effect of elevated temperature on the snail–periphyton–macrophyte relationship in summer differs among macrophyte species in active growth or senescent species in subtropical lakes and that snails, when abundant, improve the chances of maintaining actively growing macrophytes under eutrophic conditions, and more so in a warmer future with potentially denser growth of periphyton.


Cremona, F., Kõiv, T., Kisand, V., Laas, A., Zingel, P., Agasild, H., Feldmann, T., Järvalt, A., Nõges, P., Nõges, T. (2014) From Bacteria to Piscivorous Fish: Estimates of Whole-Lake and Component-Specific Metabolism with an Ecosystem Approach, PLOS one, http://dx.doi.org/10.1371/journal.pone.0101845

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From Bacteria to Piscivorous Fish: Estimates of Whole- Lake and Component-Specific Metabolism with an Ecosystem Approach

The influence of functional group specific production and respiration patterns on a lake's metabolic balance remains poorly investigated to date compared to whole-system estimates of metabolism. We employed a summed component ecosystem approach for assessing lake-wide and functional group-specific metabolism (gross primary production (GPP) and respiration (R)) in shallow and eutrophic Lake Võrtsjärv in central Estonia during three years. Eleven functional groups were considered: piscivorous and benthivorous fish; phyto-, bacterio-, proto- and metazooplankton; benthic macroinvertebrates, bacteria and ciliates; macrophytes and their associated epiphytes. Metabolism of these groups was assessed by allometric equations coupled with daily records of temperature and hydrology of the lake and measurements of food web functional groups biomass. Results revealed that heterotrophy dominated most of the year, with a short autotrophic period observed in late spring. Most of the metabolism of the lake could be attributed to planktonic functional groups, with phytoplankton contributing the highest share (90% of GPP and 43% of R). A surge of protozooplankton and bacterioplankton populations forming the microbial loop caused the shift from auto- to heterotrophy in midsummer. Conversely, the benthic functional groups had overall a very small contribution to lake metabolism. We validated our ecosystem approach by comparing the GPP and R with those calculated from O2 measurements in the lake. Our findings are also in line with earlier productivity studies made with 14C or chlorophyll a (chl-a) based equations. Ideally, the ecosystem approach should be combined with diel O2 approach for investigating critical periods of metabolism shifts caused by dynamics in food-web processes.


Cremona, F., Laas, A., Nõges, P., Nõges, T. (2014) High-frequency data within a modeling framework: On the benefit of assessing uncertainties of lake metabolism, Ecological Modelling 294, 27-35, http://dx.doi.org/10.1016/j.ecolmodel.2014.09.013

ResearchGate

High-frequency data within a modeling framework: On the benefit of assessing uncertainties of lake metabolism

We used a Bayesian metabolic model for assessing the gross primary production (GPP), ecosystem respiration (ER) and their uncertainties in lake Võrtsjärv, a large eutrophic lake in Estonia (North-eastern Europe). Diel cycle modeling was based on high-frequency (10-min) measurements of irradiance, water temperature and dissolved oxygen during most of the growing season (from May to August 2011). Posterior distribution of production and respiration was successfully simulated with the model and displayed with highly credible intervals (2.5 and 97.5 percentiles). Considering the mean GPP and ER values, the lake was autotrophic from May to June, at equilibrium in July, and heterotrophic in August. However, adding the uncertainty to metabolism estimates revealed that an ambiguous metabolic state (no clear monthly predominance of auto- or hetero-trophy) represented between 12 and 32% of the period. It is thus incautious to conclude about lake metabolic state in these conditions. A comparison with the existing classical model based on dissolved oxygen measurements showed that metabolic dynamics differed between the two approaches. Though the classical model recorded highest ecosystem productivity in midsummer, the Bayesian model predicted that productivity peaked earlier in the season and gradually declined as the irradiance dropped and the water temperature rose. Coupling between GPP and ER during the whole study period was very variable, resulting that, depending on the month, 50–100% of primary production was consumed in the lake. This coupling variability was caused by extensive diel fluctuation of irradiance-dependent production compared to relatively stable water temperature and respiration. The background respiration was high in spring and declined progressively in summer, reflecting lower inputs of allochthonous organic matter to the lake. With a wider use of high-frequency techniques for measuring lake ecological parameters, this kind of performant models that are able to assess lake productivity within small time steps and take into account the uncertainty, will be increasingly needed in the future.


Karus, K., Feldmann, T., Nõges, P., Zingel, P. (2014) Ciliate communities of a large shallow lake: Association with macrophyte beds, European Journal of Protistology 50, 382–394, http://dx.doi.org/10.1016/j.ejop.2014.05.002

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Ciliate communities of a large shallow lake: Association with macrophyte beds

We investigated the influence of macrophyte composition on ciliate community structure in a large, shallow, eutrophic Lake Võrtsjärv. We hypothesized that macrophyte composition must have strong influence on the dispersal of ecologically different ciliate groups in a shallow lake and that more diverse macrophyte stands cause also a greater diversity in the ciliate community. In Võrtsjärv macrophyte distribution is spatially strongly polarized both in east–west and north–south directions in relation to abiotic factors. Phragmites australis and Myriophyllum spicatum were the most widespread species occurring in most parts of the lake. Correlation of environmental, macrophyte and planktonic ciliate variables confirmed the suggested spatial gradients. More diverse macrophyte stands supported a high species richness and abundance of epiplanktonic community but showed negative influence on the number and abundance of euplanktonic ciliate taxa. Opposite trends were found relative to the abundance of P. australis. Benthic ciliates showed a similar distribution pattern to euplanktonic taxa being most abundant in sites were the Shannon–Weaver index for macrophytes was low. Strong polarizing effect of the lake's vegetation on planktonic ciliate diversity was reflected in correlations of the number of ciliate taxa as well as the numbers of eu- and epiplanktonic taxa with geographic co-ordinates.


Lin, Q., Jiang, X., Han, B.-P., Jeppesen, E. (2014) Does stocking of filter-feeding fish for production have cascading effects on zooplankton and the ecological state? A study of fourteen (sub)tropical Chinese reservoirs with contrasting nutrient levels, Hydrobiologia 736, 115-125, http://dx.doi.org/10.1007/s10750-014-1896-3

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Does stocking of filter-feeding fish for production have a cascading effect on zooplankton and ecological state? A study of fourteen (sub)tropical Chinese reservoirs with contrasting nutrient concentrations

Stocking of filter-feeding fish is a common tool used in Chinese reservoirs to increase fish production because of low natural recruitment. Whether such stocking has important negative effects on zooplankton with cascading effects on phytoplankton is debated. We compared the zooplankton communities in fourteen reservoirs with different nutrient concentrations and fish densities. Both chlorophyll a (Chla) and fish catch were positively related with total phosphorus (TP), whereas zooplankton biomass did not show a similar relationship with TP. Zooplankton seemed to be influenced by fish as high fish catches coincided with a low proportion of calanoids of the total copepod biomass, a high proportion of rotifers of the total zooplankton biomass, a low zooplankton:phytoplankton biomass ratio, and the absence of Daphnia irrespective of TP concentration. Both zooplankton biomass and most of the zooplankton:phytoplankton biomass ratios were among the lowest reported in the literature for the nutrient range studied. Furthermore, the Chla:TP ratio was higher than what is typically observed in temperate lakes. We conclude that top-down control of zooplankton is of key importance in reservoirs in South China where frequent stocking of filter-feeding fish seems to contribute to poor water quality in the form of higher algal biomass and reduced clarity.


Menezes, F. R., Borchsenius, F., Svenning, J-C., Davidson, T. A., Søndergaard, M., Lauridsen, L. T., Landkildehus, F., Jeppesen, E. (2014) Homogenization of fish assemblages in different lake depth strata at local and regional scales, Freshwater Biology 60, 745-757, http://dx.doi.org/10.1111/fwb.12526

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Homogenization of fish assemblages in different lake depth strata at local and regional scales

Eutrophication alters the trophic dynamics in lakes and may result in homogenisation of biotic communities. How nutrient enrichment drives patterns of homogenisation of fish species composition at within-lake (local) and among-lake (regional) scales is, however, not well studied. To test for homogenisation in fish communities, we analysed number, biomass and individual mean body mass of the different fish species present in 53 Danish lakes with contrasting depths, surface area and eutrophication. A combination of uni- and multivariate techniques revealed that eutrophication homogenises fish community composition in the littoral zone of both shallow and deep lakes at within- and among-lake scales, a notable contrast being that community composition was not homogenised in the offshore in deep lakes. In addition, fish species richness and diversity converged with progressive eutrophication and mean lake depth in all lake zones. For deep lakes, surface area was positively related to increasing differences in fish species richness and diversity. Increased homogeneity of this key assemblage may have profound implications for ecosystems and their stability (such as decreased resilience to disturbance, reduced biological complexity and increased vulnerability to large-scale and stochastic environmental events). Thus, to fully understand the impacts of eutrophication on aquatic communities at both local and regional scales, the effects of nutrient enrichment on compositional heterogeneity should be considered.


Özen, A., Bucak, T., Tavşanoğlu, Ü. N., Çakıroğlu, A. İ, Levi, E. E., Coppens, J., Jeppsen, E., Beklioğlu, M. (2014) Water level and fish-mediateed cascading effects on the microbial community in eutrophic warm shallow lakes: a mesocosm experiment, Hydrobiologia 740, 25-35, http://dx.doi.org/10.1007/s10750-014-1934-1

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Water level and fish-mediated cascading effects on the microbial community in eutrophic warm shallow lakes: a mesocosm experiment

Information on the effects of water level changes on microbial planktonic communities in lakes is limited but vital for understanding ecosystem dynamics in Mediterranean lakes subjected to major intra-and inter-annual variations in water level. We performed an in situ mesocosm experiment in an eutrophic Turkish lake at two different depths crossed with presence/absence of fish in order to explore the effects of water level variations and the role of top-down regulation at contrasting depths. Strong effects of fish were found on zooplankton, weakening through the food chain to ciliates, HNF and bacterioplankton, whereas the effect of water level variations was overall modest. Presence of fish resulted in lower biomass of zooplankton and higher biomasses of phytoplankton, ciliates and total plankton. The cascading effects of fish were strongest in the shallow mesocosms as evidenced by a lower zooplankton contribution to total plankton biomass and lower zooplankton:ciliate and HNF:bacteria biomass ratios. Our results suggest that a lowering of the water level in warm shallow lakes will enhance the contribution of bacteria, HNF and ciliates to the plankton biomass, likely due to increased density of submerged macrophytes (less phytoplankton); this effect will, however, be less pronounced in the presence of fish.


Olsen, S., Chan, F., Li, W., Zhao, S., Søndergaard, M., Jeppsen, E. (2014) Strong impact of nitrogen loading on submerged macrophytes and algae: a long-term mesocosm experiment in a shallow Chinese lake, Freshwater Biology, http://dx.doi.org/10.1111/fwb.12585

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Strong impact of nitrogen loading on submerged macrophytes and algae: a long-term mesocosm experiment in a shallow Chinese lake

We studied the effect of N loading on macrophytes (dominated by Potamogeton lucens and Cabomba caroliniana), periphyton, filamentous algae and phytoplankton in mesocosms over 10 months (starting in October) in subtropical China (Wuhan). There were three N treatments: controls (CN) without nitrogen addition (mean TN = 1.9 mg L−1), low nitrogen (LN) addition (mean TN = 3.5 mg L−1) and high nitrogen (HN) addition (mean TN = 5.5 mg L−1). Total phosphorus (TP) concentration in the water column remained moderate (0.05–0.07 mg L−1) during the experiment in all treatments. Macrophyte abundance declined in the LN and HN treatments in the first 6 months, but not in controls, followed by a partial recovery in the LN treatments. They disappeared completely in the HN treatments the following summer. Periphyton (biofilm on plastic) and phytoplankton biomass remained unaffected during the first 6 months but increased over the summer by two or three times, compared with controls, in low and high nitrogen treatments, respectively. By contrast, the abundance of filamentous algae increased over winter but declined during the summer with no obvious relationship to the N treatments. There was no difference in the TN or nitrate concentrations or soluble protein, soluble sugar and Chl-a content of P. lucens leaves and stems with increasing N load.Macrophyte populations are partially resilient to abrupt increases in N loading at moderate TP concentrations, but, after prolonged exposure, a complete collapse occurs. Our results further indicate that macrophyte loss is exacerbated by shading by filamentous algae during the winter, and by phytoplankton and periphyton in the summer, while there was no indication of direct N toxicity.


Olsen, S., Jeppesen, E., Moss, B., Özkan, K., Beklioğlu, M., Feuchtmayr, H., González Sagrario, M., Wei, L., Larsen, S., Lauridsen, T. S., Søndergaard, M. (2014) Factors influencing nitrogen processing in lakes: an experimental approach, Freshwater Biology 60, 646-662, http://dx.doi.org/10.1111/fwb.12511

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Factors influencing nitrogen processing in lakes: an experimental approach

1. To help improve our understanding of the nitrogen cycle in lakes, particularly in the context of climate change, we analysed total nitrogen (TN) and nitrate (NO À 3 -N) data from six mesocosm experiments (in Denmark, U.K., China and Turkey) covering different climatic regions. We assessed the effects of nitrogen (N) and phosphorus (P) loading, temperature, salinity and water level on N processing. 2. Water column N loss (defined as the nitrogen processed in and lost from the water column in units of net amount processed per unit area and per unit of time, or in relative terms as the percentage loss of the total pool in 2 weeks) was particularly sensitive to external nutrient loading to the mesocosms. Mean water column TN loss at high N loading varied from 111 to 250 mg m À2 day À1 and increased with N loading. High P loading resulted in increased water column N loss, possibly because of increased uptake into plants and attached algae and sedimentation of the increased algal crop. High salinity generally decreased water column TN loss; on average, 10% more TN was in the water column at 12‰ salinity than at 2‰ salinity, while no significant effect of water level was found. 3. Only weak relationships were observed between N processing and temperature, and mesocosms limited by P accumulated more nitrogen in their water columns than those with high P loadings. Our results suggest that N processing in lakes appears to be more sensitive to features of the catchment, such as hydrology and loading, than to climatic effects related to temperature, salinity and water level.


Sandin, L., Schmidt-Kloiber, A., Svenning, J-C, Jeppesen, E., Friberg, N. (2014) A trait based approach to assess climate change sensitivity of freshwater invertebrates across Swedish ecoregions, Current Zoology 60, 221-232

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A trait-based approach to assess climate change sensitivity of freshwater invertebrates across Swedish ecoregions

Freshwater habitats and organisms are among the most threatened on Earth, and freshwater ecosystems have been subject to large biodiversity losses. We developed a Climate Change Sensitivity (CCS) indicator based on trait information for a selection of stream-and lake-dwelling Ephemeroptera, Plecoptera and Trichoptera taxa. We calculated the CCS scores based on ten species traits identified as sensitive to global climate change. We then assessed climate change sensitivity between the six main ecoregions of Sweden as well as the three Swedish regions based on Illies. This was done using biological data from 1,382 stream and lake sites where we compared large-scale (ecoregional) patterns in climate change sensitivity with potential future exposure of these ecosystems to increased temperatures using ensemble-modelled future changes in air temperature. Current (1961~1990) measured temperature and ensemble-modelled future (2100) temperature showed an increase from the northernmost towards the southern ecoregions, whereas the predicted temperature change increased from south to north. The CCS indicator scores were highest in the two northernmost boreal ecoregions where we also can expect the largest global climate change-induced increase in temperature, indicating an unfortunate congruence of exposure and sensitivity to climate change. These results are of vital importance when planning and implementing management and conservation strategies in freshwater ecosystems, e.g., to mitigate increased temperatures using riparian buffer strips. We conclude that traits information on taxa spe-cialization, e.g., in terms of feeding specialism or taxa having a preference for high altitudes as well as sensitivity to changes in temperature are important when assessing the risk from future global climate change to freshwater ecosystems


Schmutz, S., Bakken T. H., Friedrich, T., Greimel, F., Harby, A., Jungwirth, M., Meichler, A., Unfer, G., Zeiringer, B. (2014) Response of fish communities to hydrological and morphological alterations hydropeaking rivers of Austria, Rivers and Research Applications, http://dx.doi.org/10.1002/rra.2795

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Response of fish communities to hydrological and morphological alterations hydropeaking rivers of Austria. Rivers and Research Applications

Climate change asks for the reduction in the consumption of fossil-based fuels and an increased share of non-regulated renewable energy sources, such as solar and wind power. In order to back up a larger share of these intermittent sources, ‘battery services’ are needed, currently provided only in large scale by hydropower, leading to more rapid and frequent changes in flows (hydropeaking) in the downstream rivers. Increased knowledge about the ecosystem response to such operations and design of cost-effective measures is needed.We analysed the response of fish communities to hydropeaking (frequency, magnitude, ramping rate and timing) and the interaction with the habitat conditions in Austrian rivers. An index of biotic integrity (Fish Index Austria) was used to compare river sections with varying degrees of flow fluctuations under near-natural and channelized habitat conditions. The results showed that habitat conditions, peak frequency (number of peaks per year), ramping rate (water level variation) and interaction between habitat and ramping rate explained most of the variation of the Fish Index Austria. In addition, peaking during the night seems to harm fish more than peaking during the day. Fish communities in hyporhithral and epipotamal types of rivers are more affected by hydropeaking than those in metarhithral type of rivers. The results support the findings of other studies that fish stranding caused by ramping rates >15 cm h−1 are likely to be the main cause of fish community degradation when occurring more often than 20 times a year. While the ecological status degrades with increasing ramping rate in nature-like rivers, fish communities are heavily degraded in channelized rivers regardless of the ramping rate. The mitigation of hydropeaking, therefore, requires an integrative approach considering the combined effects of hydrological and morphological alterations on fish.