Sirvi Autor "Cremona, Fabien" järgi

Nüüd näidatakse 1 - 20 30

Atmospheric stilling offsets the benefits from reduced nutrient loading in a large shallow lake
(Wiley, 2020) Janatian, Nasime; Olli, Kalle; Cremona, Fabien; Laas, Alo; Nõges, Peeter; Chair of Hydrobiology and Fishery, Institute of Agricultural and Environmental Sciences
As part of a global phenomenon, a 30% decrease in average wind speed since 1996 in southern Estonia together with more frequent easterly winds resulted in 47% decrease in bottom shear stress in the large (270 km 2 ), shallow (mean depth 2.8 m), and eutrophic Lake Võrtsjärv. Following a peak in eutrophication pres- sure in the 1970s–80s, the concentrations of total nutrients were declining. Nonmetric Multidimensional Scal- ing (NMDS) ordination of a 54-year phytoplankton community composition time-series (1964–2017) revealed three distinct periods with breaking points coinciding with changes in wind and/or water level. Contrary to expectations, we detected no decrease in optically active substances that could be related to wind stilling, whereas phytoplankton biomass showed an increasing trend despite reduced nutrient levels. Here we show how opening of the “light niche,” caused by declining amount of suspended sediments, was capitalized and filled by the light-limited phytoplankton community. We suggest that wind stilling is another global factor, complemen- tary to climate warming that counteracts eutrophication mitigation in lakes and may provide a challenge to assessment of the lake ecological status.
Atmospheric stilling offsets the benefits from reduced nutrient loading in a large shallow lake
(Wiley, 2019) Janatian, Nasime; Olli, Kalle; Cremona, Fabien; Laas, Alo; Nõges, Peeter; Estonian University of Life Sciences. Institute of Agricultural and Environmental Sciences. Chair of Hydrobiology and Fishery
As part of a global phenomenon, a 30% decrease in average wind speed since 1996 in southern Estonia together with more frequent easterly winds resulted in 47% decrease in bottom shear stress in the large (270 km2), shallow (mean depth 2.8 m), and eutrophic Lake Võrtsjärv. Following a peak in eutrophication pressure in the 1970s–80s, the concentrations of total nutrients were declining. Nonmetric Multidimensional Scaling (NMDS) ordination of a 54-year phytoplankton community composition time-series (1964–2017) revealed three distinct periods with breaking points coinciding with changes in wind and/or water level. Contrary to expectations, we detected no decrease in optically active substances that could be related to wind stilling, whereas phytoplankton biomass showed an increasing trend despite reduced nutrient levels. Here we show how opening of the “light niche,” caused by declining amount of suspended sediments, was capitalized and filled by the light-limited phytoplankton community. We suggest that wind stilling is another global factor, complementary to climate warming that counteracts eutrophication mitigation in lakes and may provide a challenge to assessment of the lake ecological status.
Climate change impact on Estonian lakes : [presentation]
(Estonian University of Life Sciences, 2023) Laas, Alo; Cremona, Fabien; Maljutenko, Ilja; Raudsepp, Urmas; Uiboupin, Rivo; Ott, Ingmar
The presentation took place at the 11th International Shallow Lakes Conference.
Drainage Ratio as a Strong Predictor of Allochthonous Carbon Budget in Hemiboreal Lakes
(Springer, 2019) Cremona, Fabien; Laas, Alo; Hanson, Paul C.; Sepp, Margot; Nõges, Peeter; Nõges, Tiina; Chair of Hydrobiology and Fishery. Institute of Agricultural and Environmental Sciences
We assessed the allochthonous organic carbon (OC) budgets for thirteen hemiboreal lakes using a simple equilibrium model coupled with a Bayesian framework for estimating parameter distribution and uncertainty. Model inputs consisted of hydro- logical, bathymetric and chemical data that are easily measurable at the lake and basin scale. Among the model outputs were mean OC loads (5– 123 g m-2 y-1 ), exports (1.10-3 –108 g m-2 y-1 ), mineralization (3–12 g m-2 y-1 ), and sedimenta- tion (2–6 g m-2 y-1 ). ‘‘Active’’ lake-catchment systems received and emitted the largest amounts of allochthonous OC, whereas lakes depending mostly on atmospheric inputs exhibited much more modest OC fluxes. Simulated organic carbon retention varied accordingly from 12% in some drainage lakes to 99% in seepage lakes. Lake al- lochthonous OC loads and exports were strongly correlated to drainage ratio (catchment area/lake area, R2 : 0.89 and 0.92, respectively) and to forest ratio (catchment forested area/lake area, R2 : 0.86 and 0.89), but not to wetland ratio. The simplicity of the model makes it easily transposable to a large variety of lakes. For a better insight into carbon processing, we suggest to follow a more integrative approach accounting for interactions between lake hydrology and catchment land cover.
Effect of changing in weather conditions on Eastern Mediterranean coastal lagoon fishery
(Elsevier, 2021) Cerim, Hasan; Özdemir, Nedim; Cremona, Fabien; Öglü, Burak; Chair of Hydrobiology and Fishery
Climate change shows itself in many different ways on marine life. The fishery is also a part of marine life and affected by climate change-driven weather conditions directly or indirectly. In the present study, relationships between commercial species (grey mullet -≈90% of total capture- and gilthead seabream) that were captured from lagoon traps in Köyceğiz lagoon (Turkey) and local weather conditions were analysed. The machine learning method Random Forests (RF) was used to pre-select the model predictors. RF results showed that while temperature-related parameters, cloudy days, and wind speed were the most effective parameters, precipitation-parameters were the least important parameters for these two species catch. Generalized linear models (GLMs) were applied to each fish species with the best pre-selected parameters, with the resulting equation being used for future prediction of the two fish species. Future prediction of predictors was calculated by monthly autoregressive integrated moving average (ARIMA) and 20th/80th percentile intervals were used as the scenarios. Simulations showed that an increase in some weather parameters (wind speed, seawater temperature, maximum air temperature, cloudy days) lead to an increase in grey mullet and (wind speed) gilthead seabream catch. Models proved that the impact of the weather parameters differs for those two targeted fish species although they live in the same environment. We recommend that individual fish species (and/or catch) should be used in the models, not the whole fish yield. Moreover, the model can also be used for non-commercial species in ecosystem-based studies. Changes in weather parameters due to climate change should be monitored to make proper decision on fishery management.
Effects of environmental stressors and their interactions on zooplankton biomass and abundance in a large eutrophic lake
(Springer, 2021) Cremona, Fabien; Blank, Kätlin; Haberman, Juta; Chair of Hydrobiology and Fishery
We assessed long-term impacts of multi- ple stressors and their interaction on the zooplankton community of the large, eutrophic, cyanobacteria- dominated Lake Peipsi (Estonia, Russia). Stressor dataset consisted in time series (1997–2018) of temperature, nutrients, pH, water transparency, phy- toplankton biomass and taxonomic richness. The best predictors were selected with random forests machine- learning algorithms and the subsequent models were constructed with generalized linear modeling. We also aimed to identify graphical thresholds representing non-linear, marked responses of abundance or bio- mass to stressors. Temperature was the dominant stressor for explaining zooplankton abundance and biomass, followed by cyanobacteria biomass, total nitrogen concentration and water transparency. The effect of water temperature was positive, whereas the effect of cyanobacteria became negative after their biomass exceeded a threshold of * 2 mg l-1 . How- ever, the two stressors together had antagonistic effects on zooplankton, causing a decrease in biomass and abundance. For zooplankton, critical thresholds of total nitrogen (* 700 lg l-1 ), total phosphorus (* 70 lg l-1 ), and water transparency (* 1.4 m) after which zooplankton metrics changed drastically, were determined. These findings show that although lake warming alone could be positive for zooplankton, the necessity of reducing interacting stressors that influence harmful cyanobacteria growth and biomass, especially nitrogen loads, must be considered.
Effects of filtration timing and pore size on measured nutrient concentrations in environmental water samples
(Wiley, 2022) Reed, Megan H.; Strope, Erica K.; Cremona, Fabien; Myers, Justin A.; Newell, Silvia E.; McCarthy, Mark J.
Nutrient monitoring is important for informing management decisions to mitigate eutrophication in aquaticsystems. Many nutrient monitoring programs usefilter pore sizes that allow microorganisms to pass into sam-ples and/or wait extended times between sample collection andfiltration/preservation, allowing microbial pro-cesses to alter nutrient concentrations. Here, 34 sites were sampled to determine howfilter pore size andfiltration timing affected measured ammonium (NH4+) and orthophosphate (ortho-P) concentrations. Threefil-ter pore sizes (0.22, 0.45, and 0.70μm) were used tofilter water immediately upon collection and after 5 and22 h in a bottle. NH4+and ortho-P concentrations varied relative to“baseline”measurements (i.e., 0.22μm,field-filtered samples), both over time and with differentfilter pore sizes, and showed no predictable direction ofchange based on ambient nutrient concentration or trophic status. As expected, larger relative changes occurredwith lower ambient concentrations; however, for the entire dataset, samples with > 1μmol L 1ortho-P and>3μmol L 1NH4+were lower by 11 and 33%, respectively, which would result in reported nutrient concentra-tions that were not representative of in situ conditions. Whole-water samplesfiltered after 22 h varied up to3070% for NH4+and 480% for ortho-P from baseline concentrations. Filtering water samples with a 0.22filter(or 0.45μm, at worst), immediately upon collection, should be adopted as standard practice to ensure thatreported nutrient concentrations represent the most accurate measurement possible. Inconsistent and/or insuffi-cient sampling and sample handling procedures can lead to poorly calibrated models and misinformed manage-ment and legislative decisions.
Effects of multiple stressors on nitrate and cyanobacteria in a large shallow lake : [presentation]
(Estonian University of Life Sciences, 2022) Cremona, Fabien; Öglü, Burak; McCarthy, Mark J.; Newell, Silvia E.; Nõges, Peeter; Nõges, Tiina
Presentation at the 36th Congress of the International Society of Limnology, 7-10 August 2022, Berlin.
Effects of warming and nutrients on the microbial food web in shallowlake mesocosms
(Elsevier, 2018) Zingel, Priit; Cremona, Fabien; Nõges, Tiina; Cao, Yu; Neif, Érika M.; Coppens, Jan; Işkın, Uğur; Lauridsen, Torben; Davidson, Thomas A.; Søndergaard, Martin; Beklioglu, Meryem; Jeppesen, Erik; Centre for Limnology. Institute of Agricultural and Environmental Sciences
We analysed changes in the abundance, biomass and cell size of the microbial food web community (bacteria, heterotrophicnanoflagellates, ciliates) at contrasting nutrient concentrations and temperatures during a simulated heat wave. We used 24mesocosms mimicking shallow lakes in which two nutrient levels (unenriched and enriched by adding nitrogen and phosphorus)and three different temperature scenarios (ambient, IPCC A2 scenario and A2+%50) are simulated (4 replicates of each).Experiments using the mesocosms have been running un-interrupted since 2003. A 1-month heat wave was imitated by anextra 5◦C increase in the previously heated mesocosms (from 1st July to 1st August 2014). Changes in water temperatureinduced within a few days a strong effect on the microbial food web functioning, demonstrating a quick response of microbialcommunities to the changes in environment, due to their short generation times. Warming and nutrients showed synergisticeffects. Microbial assemblages of heterotrophic nanoflagellates and ciliates responded positively to the heating, the increasebeing largest in the enriched mesocosms. The results indicate that warming and nutrients in combination can set off complexinteractions in the microbial food web functioning.
Factors controlling the three-decade long rise in cyanobacteria biomass in a eutrophic shallow lake
(Elsevier, 2018) Cremona, Fabien; Tuvikene, Lea; Haberman, Juta; Nõges, Peeter; Nõges, Tiina; Centre for Limnology. Institute of Agricultural and Environmental Sciences. Estonian University of Life Sciences
We aimed at quantifying the importance of limnological variables in the decadal rise of cyanobacteria biomass in shallow hemiboreal lakes. We constructed estimates of cyanobacteria (blue-green algae) biomass in a large, eutrophic lake (Estonia, Northeastern Europe) from a database comprising 28 limnological variables and spanning more than 50 years of monitoring. Using a dual-model approach consisting in a boosted regression trees (BRT) followed by a generalized least squares (GLS) model, our results revealed that six variables were most influential for assessing the variance of cyanobacteria biomass. Cyanobacteria response to nitrate concentration and rotifer abundance was negative, whereas it was positive to pH, temperature, cladoceran and copepod biomass. Response to total phosphorus (TP) and total phosphorus to total nitrogen ratio was very weak, which suggests that actual in-lake TP concentration is still above limiting values. The most efficient GLS model, which explained nearly two thirds (r2 = 0.65) of the variance of cyanobacteria biomass included nitrate concentration, water temperature and pH. The very high number of observations (maximum n = 525) supports the robustness of the models. Our results suggest that the decadal rise of blue-green algae in shallow lakes lies in the interaction between cultural eutrophication and global warming which bring in-lake physical and chemical conditions closer to cyanobacteria optima.
The future depends on what we do today – Projecting Europe's surface water quality into three different future scenarios
(Elsevier, 2019) Mack, Leoni; Andersen, Hans Estrup; Beklioğlu, Meryem; Bucak, Tuba; Couture, Raoul-Marie; Cremona, Fabien; Ferreira, M. Teresa; Hutchins, Michael G.; Mischke, Ute; Molina-Navarro, Eugenio; Rankinen, Katri; Venohr, Markus; Birk, Sebastian; Chair of Hydrobiology and Fishery. Institute of Agricultural and Environmental Sciences
There are infinite possible future scenarios reflecting the impacts of anthropogenic multiple stress on our planet. These impacts include changes in climate and land cover, to which aquatic ecosystems are especially vulnerable. To assess plausible developments of the future state of European surface waters, we considered two climate sce- narios and three storylines describing land use, management and anthropogenic development (‘Consensus’, ‘Techno’ and ‘Fragmented’, which in terms of environmental protection represent best-, intermediate- and worst-case, respectively). Three lake and four river basins were selected, representing a spectrum of European conditions through a range of different human impacts and climatic, geographical and biological characteristics. Using process-based and empirical models, freshwater total nitrogen, total phosphorus and chlorophyll-a concentrations were projected for 2030 and 2060. Under current conditions, the water bodies mostly fail good ecological status. In future predictions for the Techno and Fragmented World, concentrations further increased, while concentrations generally declined for the Consensus World. Furthermore, impacts were more severe for rivers than for lakes. Main pressures identified were nutrient inputs from agriculture, land use change, inade- quately managed water abstractions and climate change effects. While the basins in the Continental and Atlantic regions were primarily affected by land use changes, in the Mediterranean/Anatolian the main driver was climate change. The Boreal basins showed combined impacts of land use and climate change and clearly reflected the climate-induced future trend of agricultural activities shifting northward. The storylines showed positive effects on ecological status by classical mitigation measures in the Consensus World (e.g. riparian shading), technical im- provements in the Techno World (e.g. increasing wastewater treatment efficiency) and agricultural extensification in the Fragmented World. Results emphasize the need for implementing targeted measures to re- duce anthropogenic impacts and the importance of having differing levels of ambition for improving the future status of water bodies depending on the societal future to be expected.
Generalist invasion in a complex lake food web
(Wiley, 2023) Kuparinen, Anna; Uusi-Heikkilä, Silva; Perälä, Tommi; Ercoli, Fabio; Eloranta, Antti P.; Cremona, Fabien; Nõges, Peeter; Laas, Alo; Nõges, Tiina; Chair of Hydrobiology and Fishery
Invasive species constitute a threat not only to native populations but also to the structure and functioning of entire food webs. Despite being considered as a global problem, only a small number of studies have quantitatively predicted the food web-level consequences of invasions. Here, we use an allometric trophic network model parameterized using empirical data on species body masses and feeding interactions to predict the effects of a possible invasion of Amur sleeper (Perccottus glenii), on a well-studied lake ecosystem. We show that the modeled establishment of Amur sleeper decreased the biomasses o ftop predator fishes by about 10%–19%. These reductions were largely explained by increased larval competition for food and Amur sleeper predation on fish larvae. In contrast, biomasses of less valued fish of lower trophic positions increased by about 0.4%–9% owing to reduced predation pressure by top piscivores. The predicted impact of Amur sleeper establishment on the biomasses of native fish species vastly exceeded the impacts of current-dayfishing pressures.
Generalist invasion in a complex lake food web : [presentation]
(University of Jyväskylä, 2023) Kuparinen, Anna; Uusi-Heikkilä, Silvia; Perälä, Tommi; Ercoli, Fabio; Eloranta, Antti; Cremona, Fabien; Nõges, Peeter; Laas, Alo; Nõges, Tiina
The presentation took place at the 11th International Shallow Lakes Conference.
How light conditions influence theoretical pelagic to benthic primary production ratios in small lakes
(Wiley, 2019) Cremona, Fabien; Laas, Alo; Kõiv, Toomas; Sepp, Margot; Nõges, Peeter; Chair of Hydrobiology and Fishery. Institute of Agricultural and Environmental Sciences
Theoretical pelagic primary production of phytoplankton and benthic primary production of periphyton were modelled for two small lakes in Estonia (Northeast Europe). Although located only 500 m apart, the water colour and light attenuation of these two lakes differed markedly. The Secchi depth (SD) in the clear-water lake was 4.5 m and only 0.47 m in the dark-water lake. The total phosphorus (TP) concentrations were, respectively, 15 μg/l and 28 μg/l. An empirical model whose inputs were morphometric, light conditions and dissolved organic carbon parameters obtained from in situ measurements was employed for the present study. The model calculated primary production with a time-step of 10 min, and a spatial resolution of 10 cm, from sunrise to sunset and from lake surface to lake bottom. The primary production of periphyton and phytoplankton was almost equal in the clear lake, whereas only phy- toplankton contributed to whole-lake primary production in the dark lake because of the stronger light attenuation in the water column. The results of the present study indicated the depth-distribution profiles differed dramatically between the two lakes. The clear lake had a deep, U-shaped curve, with the productive layer reaching considerable depth soon after sunrise and maintaining a similar profile throughout the light hours. In contrast, the dark lake production declined rapidly with increasing depth, whereas the profile changed over the day reaching the greatest depth at noon.
How long-term water level changes influence the spatial distribution of fish and other functional groups in a large shallow lake
(Elsevier, 2020) Bhele, Upendra; Öğlü, Burak; Tuvikene, Arvo; Bernotas, Priit; Silm, Maidu; Järvalt, Ain; Agasild, Helen; Zingel, Priit; Seller, Siim; Timm, Henn; Nõges, Peeter; Nõges, Tiina; Cremona, Fabien; Chair of Hydrobiology and Fishery. Institute of Agricultural and Environmental Sciences
We numerically explored the effects of long-term water level changes on biotic biomass and spatial distribution of fish in a large shallow lake. We calibrated Ecospace model (Ecopath with Ecosim modelling suite) with data from various functional groups (ranging from phytoplankton to piscivorous fish), and considered 14 different habitats. Two scenarios representing, respectively, a long-term water-level increase and decrease by 1 m were constructed and run for a period of thirty eight years (1979–2016). The results showed a very uneven spatial distribution of fish biomass in the lake, with the highest con- centration in the southern basin. The 1 m decrease scenario caused a diminution in the biomass of all groups but piscivorous fish. The 1 m increase scenario saw a weak decrease in most species biomass. Consequently, in both scenarios, long-term water level changes would be generally detrimental to the lake biota. In the context of more frequent climate-induced hydrological fluctuations, we encourage the use of these simulations as effective tools for future prediction and assessment of ecosystem-based fisheries management and ecological status maintenance of shallow lakes.
How warming and other stressors affect zooplankton abundance, biomass and community composition in shallow eutrophic lakes
(Springer Nature, 2020) Cremona, Fabien; Agasild, Helen; Haberman, Juta; Zingel, Priit; Nõges, Peeter; Nõges, Tiina; Laas, Alo; Chair of Hydrobiology and Fishery. Institute of Agricultural and Environmental Science
We aimed to investigate the influence of environmental factors and predict zooplankton biomass and abundance in shallow eutrophic lakes. We employed time series of zoo- plankton and environmental parameters that were measured monthly during 38 years in a large, shallow eutrophic lake in Estonia to build estimates of zooplankton community metrics (cladocerans, copepods, rotifers, ciliates). The analysis of historical time series revealed that air temperature was by far the most important variable for explaining zooplankton biomass and abundance, followed, in decreasing order of importance, by pH, phytoplankton biomass and nitrate concentration. Models constructed with the best predicting variables explained up to 71% of zooplankton biomass variance. Most of the predictive variables had opposing or antagonistic interactions, often mitigating the effect of temperature. In the second part of the study, three future climate scenarios were developed following different Intergovernmental Panel on Climate Change (IPCC) tem- perature projections and entered into an empirical model. Simulation results showed that only a scenario in which air temperature stabilizes would curb total metazooplankton biomass and abundance. In other scenarios, metazooplankton biomass and abundance would likely exceed historical ranges whereas ciliates would not expand. Within the metazooplankton community, copepods would increase in biomass and abundance, whereas cladocerans would lose in biomass but not in abundance. These changes in the zooplankton community will have important consequences for lake trophic structure and ecosystem functioning.
Hydrometeorological and climatic control over lake phytoplankton : the importance of time scales
(Estonian University of Life Sciences, 2021) Janatian, Nasime; Nõges, Peeter; Obrador, Biel; Cremona, Fabien; Laas, Alo; Institute of Agricultural and Environmental Sciences; Uusi-Heikkilä, Silvia (opponent)
Phytoplankton reflects changes in the environment and plays a vital role in biogeochemical cycles and the climate system. The thesis attempts to link the phytoplankton dynamics with the timing, intensity, and duration of the local forcing factors at different time scales. We highlight the influence of two extremes of the wind gradient – storms and atmospheric stilling, on lake environments and phytoplankton dynamics over short and long periods, several aspects of which are poorly understood. Until recently, atmospheric stilling as a climatic phenomenon has been largely overlooked in lakes studies. To fill this research gap, we focussed on a large shallow polymictic lake (Võrtsjärv, Estonia), that was affected by a 30% decrease in average wind speed since 1996, and for which a long-term (54 years) phytoplankton and hydrometeorological database was available. Further, a contradiction between the continuous decrease in the lake’s nutrient loading and an increasing trend in phytoplankton biomass emerged as a topic of interest for this thesis. We summarise how storms interact with and alter the dynamic of phytoplankton communities. Further, we highlight to what extent this impact can change the ecological processes (e.g., nutrient, carbon, and energy cycling) within lakes and their environmental conditions in the short and long term. Using Nonmetric Multidimensional Scaling ordination of phytoplankton community composition for the years 1964–2017, we revealed three distinct periods with breaking points coinciding with abrupt changes in the wind and/or water level. We introduced a concept of "light niche," a newly discovered mechanism of meteorological control over phytoplankton in light-limited shallow lakes. Combining the monthly phytoplankton data with daily data on hydrometeorological forcing factors — thermal, light, wind, and water-level regimes and using variance partitioning with linear mixed effect modelling (LME), we found that (i) the external forcing factors relevant for each phytoplankton variable could be individualised by having a similar variance partitioning among time scales as the particular phytoplankton variable; (ii) with the largest seasonal variation component, the dominant shade-tolerant filamentous cyanobacteria were most affected by seasonal factors such as solar irradiance and water level; (iii) the LME was proven appropriate for resolving the temporal cross-scale issues.
Impact of climate change and other ecological factors on selected fish populations and fishery in Estonian large lakes
(Estonian University of Life Sciences, 2021) Öğlü, Burak; Kaart, Tanel; Kangur, Külli; Cremona, Fabien; Institute of Agricultural and Environmental Sciences; Kuparinen, Anna (opponent); Olli, Kalle (pre-opponent)
Human activities and climate change have become the most consequential threats to freshwater ecosystems and their inhabitants, especially fish. The response of the fish population to their environment is not always straightforward because of joint effect of multiple parameters. Fish and fisheries in shallow lakes can be directly affected by changes in air temperature, and also changes can occur via other factors in lakes that are under the influence of climate change. Also, response of each fish species to those parameters can vary depending on their tolerance and adaptation. Therefore, examining complex relationships between fish and their environment plays important role at understanding the dynamic of fish population and fisheries. In this study, we aimed to determine general driving factors, including climate change impact, for fish and fishery in Estonian large lakes. Results show that although winter is one of the most affected seasons by climate change in this region, then the selected fish species and eel fishery in Estonian large lakes were more sensitive to other environmental parameters. However, since the changes in winter surface water temperature and ice formation can affect other parameters, the indirect effect should not be ignored. Nutrients, spring-summer temperature and alkalinity were the most important environmental parameters for the selected fish biomass. We found that the high blue-green algae biomass during restocking period is the strongest negative impact for the eel fishery in Lake Võrtsjärv. The impact of factors can occur subsequently in fish communities and may lead to irreversible consequences, whereas the effects of concurrent climate change and nutrient enrichment can mutually reinforce their symptoms.
Impacts of multiple stressors on freshwater biota across spatial scales and ecosystems
(Nature Publishing Group, 2020) Birk, Sebastian; Chapman, Daniel; Carvalho, Laurence; Spears, Bryan M.; Andersen, Hans Estrup; Argillier, Christine; Auer, Stefan; Baattrup-Pedersen, Annette; Banin, Lindsay; Beklioglu, Meryem; Bondar-Kunze, Elisabeth; Borja, Angel; Branco, Paulo; Bucak, Tuba; Buijse, Anthonie D.; Cardoso, Ana Cristina; Couture, Raoul-Marie; Cremona, Fabien; de Zwart, Dick; Feld, Christian K.; Ferreira, M. Teresa; Feuchtmayr, Heidrun; Gessner, Mark O.; Gieswein, Alexander; Globevnik, Lidija; Graeber, Daniel; Graf, Wolfram; Gutierrez-Canovas, Cayetano; Hanganu, Jenica; Iskin, Ugur; Jarvinen, Marko; Jeppesen, Erik; Kotamaki, Niina; Kuijper, Marijn; Lemm, Jan U.; Shenglan, Lu; Solheim, Anne Lyche; Mischke, Ute; Moe, S. Jannicke; Nõges, Peeter; Nõges, Tiina; Ormerod, Steve J.; Panagopoulos, Yiannis; Phillips, Geoff; Posthuma, Leo; Pouso, Sarai; Prudhomme, Christel; Rankinen, Katri; Rasmussen, Jes J.; Richardson, Jessica; Sagouis, Alban; Santos, Jose Maria; Schaefer, Ralf B.; Schinegger, Rafaela; Schmutz, Stefan; Schneider, Susanne C.; Schuelting, Lisa; Segurado, Pedro; Stefanidis, Kostas; Sures, Bernd; Thackeray, Stephen J.; Turunen, Jarno; Uyarra, Maria C.; Venohr, Markus; von der Ohe, Peter Carsten; Willby, Nigel; Hering, Daniel; Chair of Hydrobiology and Fishery. Institute of Agricultural and Environmental sciences
Climate and land-use change drive a suite of stressors that shape ecosystems and interact to yield complex ecological responses (that is, additive, antagonistic and synergistic effects). We know little about the spatial scales relevant for the outcomes of such interactions and little about effect sizes. These knowledge gaps need to be filled to underpin future land management decisions or climate mitigation interventions for protecting and restoring freshwater ecosystems. This study combines data across scales from 33 mesocosm experiments with those from 14 river basins and 22 cross-basin studies in Europe, producing 174 combinations of paired-stressor effects on a biological response variable. Generalized linear models showed that only one of the two stressors had a significant effect in 39% of the analysed cases, 28% of the paired-stressor combinations resulted in additive effects and 33% resulted in interactive (antagonistic, synergistic, opposing or reversal) effects. For lakes, the frequencies of additive and interactive effects were similar for all spatial scales addressed, while for rivers these frequencies increased with scale. Nutrient enrichment was the overriding stressor for lakes, with effects generally exceeding those of secondary stressors. For rivers, the effects of nutrient enrichment were dependent on the specific stressor combination and biological response vari- able. These results vindicate the traditional focus of lake restoration and management on nutrient stress, while highlighting that river management requires more bespoke management solutions.
Is fish biomass controlled by abiotic or biotic factors? Results of long- term monitoring in a large eutrophic lake
(Elsevier, 2020) Öglü, Burak; Bhele, Upendra; Järvalt, Ain; Tuvikene, Lea; Timm, Henn; Seller, Siim; Haberman, Juta; Agasild, Helen; Nõges, Peeter; Silm, Maidu; Bernotas, Priit; Nõges, Tiina; Cremona, Fabien; Chair of Hydrobiology and Fishery. Institute of Agricultural and Environmental Sciences.
Relationships between biomass and ecological factors including trophic interactions were examined to understand the dynamics of six fish species in Lake Võrtsjärv, a large shallow eutrophic lake located in Estonia (north-eastern Europe). The database contained initially 31 predictive variables that were monitored in situ for nearly forty years. The strongest predictive variables were selected by three parallel approaches: single correlation (Pearson), a multivariate method (Co-inertia analyses), and a machine learning algorithm (Random Forests), followed by a Generalized Least Squares model to determine meaningful relationships with fish biomass. Models with both additive and interactive effects were constructed. The results revealed that the indicators of degraded ecological conditions (high cyanobacteria biomass and their proportion in total phytoplankton, high summer temperature, high nutrient concentration) were negatively correlated to fish biomass. Benthic macroinvertebrates and other biotic predictors (biomass of specific fish prey and predators) were also important contributors to fish biomass dynamics. Together, abiotic and biotic factors explained 40–60% of the variance of fish biomass, depending of the species. Our findings suggest that both abiotic and biotic factors control fish biomass changes in this eutrophic lake.

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