TREICLAKE

Selle valdkonna püsiv URIhttp://hdl.handle.net/10492/7299

"Towards Research Excellence and Innovation Capacity in Studing Lake Ecosystems Functional Structures and Climate Change Impact " (1.01.2021−31.12.2023); Principal investigator: Lea Tuvikene, Estonian University of Life Sciences, Institute of Agricultural and Environmental Sciences, Chair of Hydrobiology and Fishery. Funder: European Commission

Sirvi

Nüüd näidatakse 1 - 20 26

Behavioural responses of invasive (Gmelinoides fasciatus) and native (Gammarus lacustris) amphipods to predators on different bottom substrates
(Springer Nature, 2023) Teesalu, Paul; Ercoli, Fabio; Tuvikene, Arvo
The amphipod Gmelinoides fasciatus has invaded and established in numerous large lakes in Eurasia and, in the process, has displaced the native amphipod, Gammarus lacustris. The mechanism behind its invasion success is unclear and remains an important topic for invasion ecology. Three labo- ratory experiments were conducted to determine if superior predator avoidance and different types of bottom substrate could be important factors contrib- uting to the invasion success of G. fasciatus. Our results indicate that, on gravel and sand substrates, G. fasciatus exhibited superior digging behaviour to avoid predation by fishes (perch and common roach), contrary to G. lacustris. On sandy substrate, only 9% of G. fasciatus individuals were consumed, whereas G. lacustris were consumed much more intensively at 74%. In addition, G. fasciatus exhibited a more sub- stantial reduction in activity, where the time spent in motion reduced from 37.6 to 20.8% compared to G. lacustris (from 21.8 to 17.4%) when in the presence of predatory fish kairomones. G. fasciatus movement speed was also reduced in the presence of kairomones (from 57.1 to 39.3 mm/s). However, the presence of kairomones had little effect on digging behaviour of G. fasciatus. G. fasciatus consistently demonstrated superior predator avoidance abilities over G. lacus- tris, suggesting that this mechanism might play an important role in the invasion success of G. fasciatus.
Bimodality and alternative equilibria do not help explain long-term patterns in shallow lake chlorophyll-a
(Springer Nature, 2023) Davidson, Thomas A.; Sayer, Carl D.; Jeppesen, Erik; Søndergaard, Martin; Lauridsen, Torben; Johansson, Liselotte S.; Baker, Ambroise; Graeber, Daniel
Since its inception, the theory of alternative equilibria in shallow lakes has evolved and been applied to an ever wider range of ecological and socioecological systems. The theory posits the existence of two alternative stable states or equilibria, which in shallow lakes are characterised by either clear water with abundant plants or turbid water where phytoplankton dominate. Here, we used data simulations and real-world data sets from Denmark and north-eastern USA (902 lakes in total) to examine the relationship between shallow lake phytoplankton biomass (chlorophyll-a) and nutrient concentrations across a range of timescales. The data simulations demonstrated that three diagnostic tests could reliably identify the presence or absence of alternative equilibria. The real-world data accorded with data simulations where alternative equilibria were absent. Crucially, it was only as the temporal scale of observation increased (>3 years) that a predictable linear relationship between nutrient concentration and chlorophyll-a was evident. Thus, when a longer term perspective is taken, the notion of alternative equilibria is not required to explain the response of chlorophyll-a to nutrient enrichment which questions the utility of the theory for explaining shallow lake response to, and recovery from, eutrophication.
Catchment soil characteristics predict organic carbon, nitrogen, and phosphorus levels in temperate lakes
(The University of Chicago Press, 2021) Sepp, Margot; Kõiv, Toomas; Nõges, Peeter; Nõges, Tiina; Newell, Silvia E.; McCarthy, Mark J.; Institute of Agricultural and Environmental Sciences. Estonian University of Life Sciences
Allochthonous supply of dissolved organic matter (DOM) and nutrients from the catchment have a sub- stantial impact on the physical and chemical properties of lake water. Transport of DOM and nutrients is affected by different catchment characteristics, e.g., catchment area, soil and land cover, and population density. The aim of this study was to relate geological, hydrological, land-cover, and soil characteristics of 52 temperate catchments in Estonia to variability in DOM (measured as dissolved organic carbon [DOC]), total organic nitrogen (TON), and total phosphorus (TP) in lakes and to assess the relative importance of different land-cover and soil types as sources of these substances. DOC, TON, and TP were very diverse in the studied lakes. Strong positive correlation between DOC and TON indicated that these substances had similar concentration patterns and sources. Catchment soil cover was the best predictor of DOC, TON, and TP levels in lakes, explaining up to 43.8% of their variabilities. This obser- vation can partly be explained by different soil organic carbon (SOC) content: soils with higher SOC were associated with higher lake DOC and TON, whereas soils with low SOC corresponded to lower DOC and TON. Similar to other temperate lakes, bogs and peat soils were a major source of DOM in our studied lakes. DOC, TON, and color were positively associated with percentages of peat soils in the catchment. On the other hand, TP increased with the pro- portion of urban areas in the catchments, indicating the importance of human impact on its concentration. Under- standing the impact of different catchment characteristics on DOC, TON, and TP in temperate lakes is crucial for developing transport models used for predicting future levels of DOM and nutrients under changing climate and land use.
Causal networks of phytoplankton diversity and biomass are modulated by environmental context
(Nature Research, 2022) Chang, Chun-Wei; Miki, Takeshi; Ye, Hao; Souissi, Sami; Adrian, Rita; Anneville, Orlane; Agasild, Helen; Ban, Syuhei; Be’eri-Shlevin, Yaron; Chiang, Yin-Ru; Feuchtmayr, Heidrun; Gal, Gideon; Ichise, Satoshi; Kagami, Maiko; Kumagai, Michio; Liu, Xin; Matsuzaki, Shin-Ichiro S.; Manca, Marina M.; Nõges, Peeter; Piscia, Roberta; Rogora, Michela; Shiah, Fuh-Kwo; Thackeray, Stephen J.; Widdicombe, Claire E.; Wu, Jiunn-Tzong; Zohary, Tamar; Hsieh, Chih-hao
Untangling causal links and feedbacks among biodiversity, ecosystem functioning, and environmental factors is challenging due to their complex and context-dependent interactions (e.g., a nutrient-dependent relationship between diversity and biomass). Consequently, studies that only consider separable, unidirectional effects can produce divergent conclusions and equivocal ecological implications. To address this complexity, we use empirical dynamic modeling to assemble causal networks for 19 natural aquatic ecosystems (N24°~N58°) and quantified strengths of feedbacks among phytoplankton diversity, phytoplankton biomass, and environmental factors. Through a cross-system comparison, we identify macroecological patterns; in more diverse, oligotrophic ecosystems, biodiversity effects are more important than environmental effects (nutrients and temperature) as drivers of biomass. Furthermore, feedback strengths vary with productivity. In warm, productive systems, strong nitratemediated feedbacks usually prevail, whereas there are strong, phosphate-mediated feedbacks in cold, less productive systems. Our findings, based on recovered feedbacks, highlight the importance of a network view in future ecosystem management.
Changes in nutrient concentration and water level affect the microbial loop: a 6‑month mesocosm experiment
(Springer, 2023) Zingel, Priit; Jeppesen, Erik; Nõges, Tiina; Hejzlar, Josef; Tavşanoğlu, Ülkü Nihan; Papastergiadou, Eva; Scharfenberger, Ulrike; Agasild, Helen
Eutrophication and lake depth are of key importance in structuring lake ecosystems. To elucidate the effect of contrasting nutrient concentrations and water levels on the microbial community in fully mixed shallow lakes, we manipulated water depth and nutrients in a lake mesocosm experiment in north temperate Estonia and followed the microbial community dynamics over a 6-month period. The experiment was carried out in Lake Võrtsjärv—a large, shallow eutrophic lake. We used two nutrient levels crossed with two water depths, each represented by four replicates. We found treatment effects on the microbial food web structure, with nutrients having a positive and water depth a negative effect on the biomasses of bacterial and heterotrophic nanoflagellates (HNF) (RM-ANOVA, p < 0.05). Nutrients affected positively and depth negatively the mean size of individual HNF and ciliate cells (RM-ANOVA; p < 0.05). The interactions of depth and nutrients affected positively the biomass of bacterivorous and bacteriherbivorous ciliates and negatively the biomass of predaceous ciliates (RM-ANOVA; p < 0.05). Bacterivorous ciliates had lowest biomass in shallow and nutrient-rich mesocosms, whilst predaceous ciliates had highest biomass here, influencing trophic interactions in the microbial loop. Overall, increased nutrient concentrations and decreased water level resulted in an enhanced bacterial biomass and a decrease in their main grazers. These differences appeared to reflect distinctive regulation mechanisms inside the protozoan community and in the trophic interactions in the microbial loop community.
Changes in nutrient concentration and water level affect the microbial loop: a multi-seasonal mesocosm experiment : [submitted version]
(Springer, 2023) Zingel, Priit; Jeppesen, Erik; Nõges, Tiina; Hejzlar, Josef; Tavşanoğlu, Ülkü Nihan; Papastergiadou, Eva; Scharfenberger, Ulrike; Agasild, Helen; Centre for Limnology
Eutrophication and lake depth are of key importance in structuring lake ecosystems. To elucidate the effect of contrasting nutrient concentrations and water levels on the microbial community, we manipulated water depth and nutrients in a mesocosm experiment in north temperate Estonia and followed the microbial community dynamics during a 6-month period. We used two nutrient levels crossed with two water depths, each represented by four replicates. We found treatment effects on the microbial food web structure, with nutrients having a positive and water depth a negative effect on bacterial biomass, heterotrophic nanoflagellates (HNF) and metazooplankton biomass. Nutrients and water depth had both positive impacts on phytoplankton biomass. Bacterivorous ciliates had lowest biomass in shallow and nutrient rich mesocosms, whilst predaceous ciliates had highest biomass here, influencing trophic interactions in the microbial loop. Overall, increased nutrient concentrations and decreased water level resulted in an enhanced bacterial biomass and a decrease in their main grazers. These differences appeared to reflect distinctive regulation mechanisms inside the protozoan community and in the trophic interactions in the microbial loop community.
The comparison of the feeding of European perch Perca fluviatilis L. larvae in littoral and pelagic habitats of northern temperate lakes
(Estonian Academy Publishers, 2022) Karus, Katrit; Zagars, Matiss; Agasild, Helen; Feldmann, Tõnu; Tuvikene, Arvo; Puncule, Linda; Zingel, Priit; Chair of Hydrobiology and Fishery; Centre for Limnology
We studied the feeding of European perch Perca fluviatilis L. larvae in littoral and pelagic habitats of four different lakes – one Latvian (Auciema) and three Estonian (Akste, Kaiavere, and Prossa). Altogether, 162 perch larvae (81 from both habitats) were collected to estimate the diet composition of gathered larval specimens in spring (2019) using gut content analysis via epifluorescence microscopy. Attention was paid particularly to the question how does the larval perch food composition differ in pelagic and littoral habitats. We hypothesized that the consumption of zooplankton is higher and the larval condition is better in littoral habitats. We assessed the feeding on both protozoo- (ciliates) and metazooplankton and applied multiple indices (Hurlbert’s standardized niche breadth, Ivlev’s selectivity and relative importance index) to evaluate, respectively, the larval fish prey importance, feeding homogeneity and strategies. The results showed that larval length and weight were slightly higher and body condition was slightly better in the lakes’ littoral habitats. The feeding niche of perch larvae was narrower in the littoral, which can indicate more favourable feeding conditions in littoral than lake pelagic habitats. While the small cladocerans (Bosmina longirostris Müller) were generally the preferred and important food objects, ciliates were avoided and consumed only when their share in the total zooplankton biomass was >40%. However, in shortage of cladocerans, ciliates could be vitally important food objects for perch larvae.
Diet and trophic niche of the invasive signal crayfish in the first invaded Italian stream ecosystem
(Nature, 2021) Ercoli, Fabio; Ghia, Daniela; Gruppuso, Laura; Fea, Gianluca; Bo, Tiziano; Ruokonen, Timo J.
The occurrence of the signal crayfsh Pacifastacus leniusculus in the Valla Stream was the frst established population of this invasive species recorded in an Italian stream ecosystem. We evaluated the seasonality of diet and trophic niche of invasive signal crayfsh in order to estimate the ecological role and efects on native communities of the stream ecosystem. We studied the diferences in food source use between sexes, life stages and seasons using carbon and nitrogen stable isotope analyses. To supplement stable isotope analyses, we evaluated food source usage using traditional stomach content analysis. We tested the hypothesis that juveniles have a diferent diet, showing diferent trophic niches, compared to adults. Results indicated that signal crayfsh adult and juvenile diets mainly rely on macroinvertebrates and periphyton in summer, shifting to mostly periphyton in autumn. Although the two age classes occupied an equivalent trophic niche, juveniles showed slightly diferent carbon isotope values, suggesting a somewhat ontogenetic shift consistent among seasons. No signifcant diferences were found in adult and juvenile diets between summer and autumn seasons. Our fndings suggest that signal crayfsh juveniles and adults exhibited seasonal feeding habits, probably due to ecological behaviour rather than food resource availability, and that both are likely to impose similar efects on macroinvertebrate communities in this and similar stream ecosystems
The diet of Eurasian perch larvae in lakes with different zooplankton assemblages
(2023) Zingel, Priit; Agasild, Helen; Zagars, Matiss; Feldmann, Tõnu; Tuvikene, Arvo; Zingel, Tiina; Puncule, Linda; Karus, Katrit; Centre for Limnology. Institute of Agricultural and Environmental Sciences. Chair of Hydrobiology and Fishery. Estonian University of Life Sciences
Eurasian perch has a great ecological importance in freshwaters as it is often a dominating predatory fish in ecosystems. The knowledge of perch feeding patterns, strategies, and adaptivity to food environment in their early life stages is essential to understand its population development and dynamics. It has been demonstrated that there exists a positive relationships between preferred prey availability and larval feeding success. We examined the diet of larval perch in their natural habitats of different zooplankton assemblages in three small lakes with varying ecological status. In each lake, both pelagial and littoral were studied. We found significant relation between zooplankton biomass in the lake and zooplankton biomass consumed by fish larvae. The most important food objects were crus- taceans (Bosmina longirostris, Chydorus sphaericus). Ciliates were consumed only in one lake. Our results show that perch larvae are flexible in their choice of food and can adapt to different food environments.
Differences on the level of hepatic transcriptome between two flatfish species in response to liver cancer and environmental pollution levels
(Elsevier, 2023) Sepp, Tuul; Baines, Ciara; Kreitsberg, Randel; Scharsack, Jörn Peter; Nogueira, Pedro; Lang, Thomas; Fort, Jérôme; Sild, Elin; Clarke, John T.; Tuvikene, Arvo; Meitern, Richard
Environmental factors can cause cancer in both wild animals and humans. In ecological settings, genetic variation and natural selection can sometimes produce resilience to the negative impacts of environmental change. An increase in oncogenic substances in natural habitats has therefore, unintentionally, created opportunities for using polluted habitats to study cancer defence mechanisms. The Baltic and North Sea are among the most contaminated marine areas, with a long history of pollution. Two flatfish species (flounder, Platichthys flesus and dab, Limanda limanda) are used as ecotoxicological indicator species due to pollution-induced liver cancer. Cancer is more prevalent in dab, suggesting species-specific differences in vulnerability and/or defence mechanisms. We conducted gene expression analyses for 30 flatfishes. We characterize between- and within-species patterns in potential cancer-related mechanisms. By comparing cancerous and healthy fishes, and noncancerous fishes from clean and polluted sites, we suggest also genes and related physiological mechanisms that could contribute to a higher resistance to pollution-induced cancer in flounders. We discovered changes in transcriptome related to elevated pollutant metabolism, alongside greater tumour suppression mechanisms in the liver tissue of flounders compared to dabs. This suggests either hormetic upregulation of tumour suppression or a stronger natural selection pressure for higher cancer resistance for flounders in polluted environment. Based on gene expression patterns seen in cancerous and healthy fish, for liver cancer to develop in flounders, genetic defence mechanisms need to be suppressed, while in dabs, analogous process is weak or absent. We conclude that wild species could offer novel insights and ideas for understanding the nature and evolution of natural cancer defence mechanisms.
Effects of environmentally relevant concentrations of microplastics on amphipods
(Elsevier, 2022) Rani-Borges, Barbara; Meitern, Richard; Teesalu, Paul; Raudna-Kristoffersen, Merilin; Kreitsberg, Randel; Heinlaan, Margit; Tuvikene, Arvo; Ivask, Angela
Lack of microplastics (MP) toxicity studies involving environmentally relevant concentrations and exposure times is concerning. Here we analyzed the potential adverse effects of low density polyethylene (LDPE) MP at environmentally relevant concentration in sub-chronic exposure to two amphipods Gmelinoides fasciatus and Gammarus lacustris, species that naturally compete with each other for their habitats. 14-day exposure to 2 μg/L (8 particles/L corresponding to low exposure) and 2 mg/L (~8400 particles/L, corresponding to high exposure) of 53–100 μm LDPE MP were used to assess ingestion and egestion of MP, evaluate its effects on amphipod mortality, swimming ability and oxidative stress level. Both amphipod species were effectively ingesting and egesting LDPE MP. On the average, 0.8 and 2.5 MP particles were identified in the intestines of each amphipod exposed to 2 μg/L and 2 mg/L LDPE MP, respectively. Therefore, intestinal MP after 14-day exposure did not fully reflect the differences in LDPE MP exposure concentrations. Increased mortality of both amphipods was observed at 2 mg/L LDPE MP and in case of G. lacustris also at 2 μg/L exposure. The effect of LDPE on swimming activity was observed only in case of G. fasciatus. Oxidative stress marker enzymes SOD, GPx and reduced glutathione GSH varied according to amphipod species and LDPE MP concentration. In general G. lacustris was more sensitive towards LDPE MP induced oxidative stress. Overall, the results suggested that in MP polluted environments, G. lacustris may lose its already naturally low competitiveness and become overcompeted by other more resistant species. The fact that in the sub-chronic foodborne exposure to environmentally relevant and higher LDPE MP concentrations all the observed toxicological endpoints were affected refers to the potential of MP to affect and disrupt aquatic communities in the longer perspective.
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.
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.
The impact of climate change and eutrophication on phosphorus forms in sediment: Results from a long-term lake mesocosm experiment
(Elsevier, 2022) Saar, Katrin; Nõges, Peeter; Søndergaard, Martin; Jensen, Maria; Jørgensen, Charlotte; Reitzel, Kasper; Jeppesen, Erik; Lauridsen, Torben L.; Jensen, Henning S.; Centre for Limnology. Estonian University of Life Science
Characteristics of bottom sediments in lake mesocosms 11 years after starting the experiment were studied in order to determine the effects of nutrient loading, temperature increase and vegetation type on concentration and vertical dis- tribution of phosphorus (P) forms. The experimental setup consisted of 24 outdoor flow-through mesocosms with two nutrient treatments – low (L) and high (H) and 3 temperature levels – ambient (T0), heated by 2–4 °C (T1) and 3–6 °C (T2) in four replicates. Thickness of the organic sediment was measured and the sediment analysed for dry weight, or- ganic matter, and P fractions (according to a sequential extraction scheme) and organic P compounds (by ³¹P nuclear magnetic resonance spectroscopy). Higher nutrient loading led to increased sediment accumulation and higher con- centration of total P and most P fractions, except P bound to aluminium and humic matter. The dominant vegetation type covaried with nutrient levels. Vertical gradients in Ca bound P and mobile P in low nutrient mesocosms was per- haps a result of P coprecipitation with calcite on macrophytes and P uptake by roots indicating that in macrophyte-rich lakes, plants can be important modifiers of early P diagenesis. Temperature alone did not significantly affect sediment accumulation rate but the interaction effect between nutrient and temperature treatments was significant. At high nu- trient loading, sediment thickness decreased with increasing temperature, but at low nutrient loading, it increased with warming. The effect of warming on sediment composition became obvious only in nutrient enriched mesocosms showing that eutrophication makes shallow lake ecosystems more susceptible to climate change.
The influence of macrophyte ecological groups on food web components of temperate freshwater lakes
(Elsevier, 2022) Karus, Katrit; Zagars, Matiss; Agasild, Helen; Tuvikene, Arvo; Zingel, Priit; Puncule, Linda; Medne-Peipere, Madara; Feldmann, Tõnu
Aquatic macrophyte taxonomic composition, species abundance and cover determine the physical structure, complexity and heterogeneity of aquatic habitats – the structuring role of macrophytes. These traits influence richness, distribution, feeding and strength of the relationships between food web communities in lakes. The aim of this study was to determine how lakes with different dominating macrophyte ecological groups affect planktonic food web components, emphasising the influence on young of year (YOY) fish and large (≥1 +) fish community. We hypothesised that different dominating macrophyte ecological groups have different structural effects on food web components and YOY fish growth, abundance and feeding. Studied lakes categorised into three different macrophyte ecological groups – lakes dominated by emergent, floating+floating-leaved or submerged vegetation. We found that all dominating ecological groups had a strong influence on plankton communities (except heterotrophic bacterioplankton and nanoflagellates), YOY fish and large fish. Floating-leaved plant dominance was positively related to planktonic food web structure and YOY fish weight, length, abundance and the consumption of zooplankton as a prey of all major species of YOY fishes. Larger fish tended to favour the presence of emergent vegetation. This conclusion has important implications for local managers and conservationists in respect to the maintenance and protection of littoral habitats and fish resources.
Long-term data reflect nitrogen pollution in Estonian rivers
(IWA Publishing, 2022) Nõges, Tiina; Vilbaste, Sirje; McCarthy, Mark J.; Tamm, Marju; Nõges, Peeter
We analysed long-term (1992–2020) changes in fertiliser use, wastewater treatment, and river water nutrient status in Estonia (N-E Europe) in the context of changing socio-economic situations and legislation. We hypothesised that improved regulation of fertiliser usage and wastewater treatment are reflected as declining riverine nutrient concentrations, with the largest relative improvements occurring in catchments with initially high proportions of point source loading. We analysed nutrient dynamics in 16 rivers differing by catchment land use, population and livestock densities. Data on fertiliser use and wastewater treatment originated from the Statistics Estonia database, and riverine nutrient concentrations from the State Environmental Monitoring Database. We clustered the rivers by their catchment properties and analysed trends in their nutrient status. Point source nutrient loading reductions explained most of the decline in riverine nutrient concentrations, whereas application of mineral fertilisers has increased, hindering efforts to reach water quality and nutrient load targets set by the EU Water Framework Directive and the Baltic Sea Action Plan. Highest nitrogen concentrations and strongest increasing trends were found in rivers within the Nitrate Vulnerable Zone, indicating violation of the EU Nitrates Directive. To comply with these directives, resource managers must address non-point source nutrient loading from river watersheds.
Niche partitioning of invasive Amur sleeper (Perccottus glenii) amongst native fish communities in three different freshwater ecosystems
(Pensoft Publishers, 2024) Ercoli, Fabio; Kiljunen, Mikko; Teesalu, Paul; Tuvikene, Arvo; Tambets, Meelis; Kärgenberg, Einar; Nõges, Tiina
The invasive fish, Amur sleeper, poses a significant and growing threat to Central European freshwater ecosystems. Despite its rapid spread, the ecological implications of its invasion have been poorly explored. Recent findings confirm its presence in various Estonian freshwater systems, raising concerns about its imminent expansion into larger lakes. To better understand its potential ecological impacts, we explored the isotopic niche of the Amur sleeper in comparison with native fish species co-existing in three Estonian freshwater ecosystems. We employed carbon and nitrogen stable isotope analyses alongside gut content analyses. Our findings show that the Amur sleeper’s diet in newly-invaded Estonian water bodies predominantly comprises benthic macroinvertebrates, although it may also include fish, confirming its role as a predator in the local food web. Notably, Amur sleeper populations exhibited clear isotopic niche partitioning in three invaded ecosystems. A logistic regression model, based on stomach content analyses, revealed an ontogenetic diet shift from benthivorous to piscivorous feeding habits from small to large specimens. Amur sleeper exhibits voracious, non-selective feeding habits, which can negatively impact native freshwater communities. The ability to occupy a distinct isotopic niche, with minimal overlap with native fish populations, may reduce interspecific competition, facilitating the spread and establishment of Amur sleeper in newly-invaded habitats. Managing the spread of this invasive species thus becomes even more critical to safeguard the integrity of native aquatic ecosystems.
Nitrate as a predictor of cyanobacteria biomass in eutrophic lakes in a climate change context
(Elsevier, 2022) Cremona, Fabien; Öğlü, Burak; McCarthy, Mark J.; Newell, Silvia E.; Nõges, Peeter; Nõges, Tiina; Chair of Hydrobiology and Fishery. Institute of Agricultural and Environmental Sciences. Estonian University of Life Science
We aimed to predict cyanobacteria biomass and nitrate (NO₃) concentrations in Lake Võrtsjärv, a large, shallow, and eutrophic lake in Estonia. We used a model chain based on the succession of a mechanistic (INCA-N) model and an empirical, generalized linear model. INCA-N model calibration and validation was performed with long term climate and catchment parameters. We constructed twelve scenarios as combinations of climate forcing from the Intergovernmental Panel on Climate Change (IPCC, 3 scenarios), land conversion (forest to agriculture, 2 scenarios), and fertilizer use (2 scenarios).Models predicted 46% of the variance of cyanobacteria biomass and 65% of that of NO₃ concentrations. The model chain simulated that scenarios comprising both forest conversion to agricultural lands and a greater use of fertilizer per surface area unit would cause increases in lacustrine NO₃ (up to twice the historicalmean) and cyanobacteria biomass (up to a four-fold increase compared to the historical mean). The changes in NO₃ concentrations and cyanobacteria biomass were more pronounced in low and moderate warming scenarios than in high warming scenarios because of increased denitrification rates in a warmer climate. Our findings show the importance of reducing anthropogenic pressures on lake catchments in order to reduce harmful pollutant and microalgae proliferation, and highlight the counterintuitive effects of multiple stressor interactions on lake functioning.
Opportunities for combining data of Estonian and Russian monitoring to reflect on water quality in large transboundary Lake Peipsi
(Elsevier, 2022) Tammeorg, Olga; Tuvikene, Lea; Kondratyev, Sergey; Golosov, Sergey; Zverev, Ilya; Zadonskaya, Olga; Nõges, Peeter
Lake Peipsi, one of the world’s largest lakes, is shared between Estonia and Russia. The water quality in different parts of the lake has so far been assessed independently. Here we explore opportunities for combining data of Estonian and Russian monitoring. For that, we 1) analysed the compatibility of data for some water quality variables; 2) estimated the potential effects of the differences in sampling frequency; 3) provided a few regression models to calculate the missing data for months not sampled by the Russian side. Data of the concurrent Estonian and Russian sampling indicated a good compatibility. Estonian data analysis suggested that water quality assessment results are sensitive to sampling frequency. For example, total phosphorus (TP) in the largest basin showed a long-term decreasing trend in three month data that disappeared when data for other months were added. Disregarding some months may lead to underor overestimation of certain factors with no consistency in the response of different basins. Hence, data of the whole ice-free period are recommended for an adequate water quality assessment. Furthermore, we demonstrated that monthly values of the water quality variables of the same year are autocorrelated. Based on this, we filled the gaps in the long-term data and compiled a dataset for the whole lake that enables its most comprehensive use in water quality assessment and management. Long-term data revealed no water quality improvement of Lake Peipsi. Further reduction of the external nutrient load is needed. Eutrophication is sustained by high internal phosphorus load.
Pelagic niche shift by fishes following restorations of a eutrophic lake
(Springer, 2024) Berthelsen, Andreas S.; Søndergaard, Martin; Kiljunen, Mikko; Eloranta, Antti; Lauridsen, Torben
Lake restoration by biomanipulation or phosphorus fixation has been commonly applied methods to improve the ecological status of lakes. However, the effects of lake restoration on foodweb dynamics are still poorly understood, especially when biomanipulation and nutrient fixation are used simultaneously. This study investigated the combined effects of a 70% fish removal (mainly roach (Rutilus rutilus Linnaeus, 1758) and bream (Abramis brama Linnaeus, 1758) and Phoslock® treatment on fish trophic ecology in Lyngsø (area: 9.6 ha, mean depth: 2.6 m), Denmark. The lake restoration resulted in decreased nutrient levels, increased water clarity, and increased coverage of more structurally complex submerged macrophytes. Following lake restoration, significant changes in diets of the dominant fish species were observed. Stomach content analyses of roach and perch (Perca fluviatilis Linnaeus, 1758) revealed significantly reduced detritus utilization and increased foraging on macrophytes and macrophyte living invertebrates. Results from stable isotope mixing models indicated a shift from littoral benthic to more pelagic food resources by the dominant fish species. Our findings provide further evidence that lake restorations can lead to substantial changes in lake food webs and fish communities, thereby potentially facilitating a shift toward an ecological state resembling the pristine reference state, less influenced by anthropogenic factors.

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