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Plastic debris is thought to be widespread in freshwater ecosystems globally 1 . However, a lack of comprehensive and comparable data makes rigorous assessment of its distribution challenging 2,3 . Here we present a standardized cross-national survey that assesses the abundance and type of plastic debris (>250 μm) in freshwater ecosystems. We sample surface waters of 38 lakes and reservoirs, distributed across gradients of geographical position and limnological attributes, with the aim to identify factors associated with an increased observation of plastics. We find plastic debris in all studied lakes and reservoirs, suggesting that these ecosystems play a key role in the plastic-pollution cycle. Our results indicate that two types of lakes are particularly vulnerable to plastic contamination: lakes and reservoirs in densely populated and urbanized areas and large lakes and reservoirs with elevated deposition areas, long water-retention times and high levels of anthropogenic influence. Plastic concentrations vary widely among lakes; in the most polluted, concentrations reach or even exceed those reported in the subtropical oceanic gyres, marine areas collecting large amounts of debris 4 . Our findings highlight the importance of including lakes and reservoirs when addressing plastic pollution, in the context of pollution management and for the continued provision of lake ecosystem services., (© 2023. The Author(s), under exclusive licence to Springer Nature Limited.)

The quality of lake ice is of uppermost importance for ice safety and under-ice ecology, but its temporal and spatial variability is largely unknown. Here we conducted a coordinated lake ice quality sampling campaign across the Northern Hemisphere during one of the warmest winters since 1880 and show that lake ice during 2020/2021 commonly consisted of unstable white ice, at times contributing up to 100% to the total ice thickness. We observed that white ice increased over the winter season, becoming thickest and constituting the largest proportion of the ice layer towards the end of the ice cover season when fatal winter drownings occur most often and light limits the growth and reproduction of primary producers. We attribute the dominance of white ice before ice-off to air temperatures varying around the freezing point, a condition which occurs more frequently during warmer winters. Thus, under continued global warming, the prevalence of white ice is likely to substantially increase during the critical period before ice-off, for which we adjusted commonly used equations for human ice safety and light transmittance through ice., (© 2022. The Author(s).)

Lake eutrophication is a pervasive problem globally, particularly serious in agricultural and densely populated areas. Whenever nutrients nitrogen and phosphorus do not limit phytoplankton growth directly, high growth rates will rapidly lead to biomass increases causing self-shading and light-limitation, and eventually CO 2 depletion. The paradigm of phytoplankton limitation by nutrients and light is so pervasively established, that the lack of nutrient limitation is ordinarily interpreted as sufficient evidence for the condition of light limitation, without considering the possibility of limitation by inorganic carbon. Here, we firstly evaluated how frequently CO 2 undersaturation occurs in a set of eutrophic lakes in the Pampa plains. Our results confirm that conditions of CO 2 undersaturation develop much more frequently (yearly 34%, summer 44%) in these agriculturally impacted lakes than in deep, temperate lakes in forested watersheds. Secondly, we used Generalized Additive Models to fit trends in CO 2 concentration considering three drivers: total incident irradiance, chlorophyll a concentration, and lake depth; in eight multi-year datasets from eutrophic lakes from Europe, North and South America, Asia and New Zealand. CO 2 depletion was more often observed at high irradiance levels, and shallow water. CO 2 depletion also occurred at high chlorophyll concentration. Finally, we identified occurrences of light- and carbon-limitation at the whole-lake scale. The different responses of chlorophyll a and CO 2 allowed us to develop criteria for detecting conditions of CO 2 limitation. For the first time, we provided whole-lake evidence of carbon limitation of phytoplankton biomass. CO 2 increases and eutrophication represent two major and converging environmental problems that have additive and contrasting effects, promoting phytoplankton, and also leading to carbon depletion. Their interactions deserve further exploration and imaginative approaches to deal with their effects., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Globally, our knowledge on lake fisheries is still limited despite their importance to food security and livelihoods. Here we show that fish catches can respond either positively or negatively to climate and land-use changes, by analyzing time-series data (1970-2014) for 31 lakes across five continents. We find that effects of a climate or land-use driver (e.g., air temperature) on lake environment could be relatively consistent in directions, but consequential changes in a lake-environmental factor (e.g., water temperature) could result in either increases or decreases in fish catch in a given lake. A subsequent correlation analysis indicates that reductions in fish catch was less likely to occur in response to potential climate and land-use changes if a lake is located in a region with greater access to clean water. This finding suggests that adequate investments for water-quality protection and water-use efficiency can provide additional benefits to lake fisheries and food security.

Over the last 3-4 decades, Lake Peipsi water (sampling site A, middle part of the lake, and site B, northern part) has experienced a statistically significant increase of bicarbonate, pH, chemical oxygen demand, nitrate (and nitrite in site B), due to combination of climate change and eutrophication. By photochemical modelling, we predicted a statistically significant decrease of radicals ·OH and CO3(-·) (site A, by 45% and 35%, respectively) and an increase of triplet states of chromophoric dissolved organic matter ((3)CDOM(∗); site B, by ∼25%). These species are involved in pollutant degradation, but formation of harmful by-products is more likely with (3)CDOM(∗) than with ·OH. Therefore, the photochemical self-cleansing ability of Lake Peipsi probably decreased with time, due to combined effects of climate change and eutrophication. In different environments (e.g. Lake Maggiore, NW Italy), ecosystem restoration policies had the additional advantage of enhancing sunlight-driven detoxification, suggesting that photochemical self-cleansing would be positively correlated with lake water quality., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

The world's 1.4 million lakes (≥10 ha) provide many ecosystem services that are essential for human well‐being; however, only if their health status is good. Here, we reviewed common lake health issues and classified them using a simple human health‐based approach to outline that lakes are living systems that are in need of oxygen, clean water and a balanced energy and nutrient supply. The main reason for adopting some of the human health terminology for the lake health classification is to increase the awareness and understanding of global lake health issues. We show that lakes are exposed to various anthropogenic stressors which can result in many lake health issues, ranging from thermal, circulatory, respiratory, nutritional and metabolic issues to infections and poisoning. Of particular concern for human well‐being is the widespread lake drying, which is a severe circulatory issue with many cascading effects on lake health. We estimated that ∼115,000 lakes evaporate twice as much water as they gain from direct precipitation, making them vulnerable to potential drying if inflowing waters follow the drying trend, putting more than 153 million people at risk who live in close vicinity to those lakes. Where lake health issues remain untreated, essential ecosystem services will decline or even vanish, posing a threat to the well‐being of millions of people. We recommend coordinated multisectoral and multidisciplinary prevention and treatment strategies, which need to include a follow‐up of the progress and an assessment of the resilience of lakes to intensifying threats. Priority should be given to implementing sewage water treatment, mitigating climate change, counteracting introductions of non‐native species to lakes and decreasing uncontrolled anthropogenic releases of chemicals into the hydro‐, bio‐, and atmosphere. Plain Language Summary: Lakes around the world come in an array of sizes, shapes and colors, each telling a unique story of geological history and environmental importance. When lakes are healthy they contribute to the achievement of the global sustainable development goals by providing many important ecosystem services. Lakes are, however, not always healthy. Here, it is shown that lakes can suffer from a large variety of health issues, ranging from thermal, circulatory, respiratory, nutritional and metabolic issues to infections and poisoning. Without improved treatment strategies, many of the health issues may become chronic, affecting millions of people who are dependent on the ecosystem services from the lakes. To prevent and cure lakes from critical health conditions, strategies that are similar to those used in human healthcare should be applied: intervention and preventative actions before health problems occur, regular screening and early identification of lake health issues, and remediation and mitigation efforts at an appropriate scale, spanning from local to global. Key Points: Anthropogenic stressors can cause lake health issues that range from thermal, circulatory, respiratory, nutritional and metabolic issues to infections and poisoningLake health varies geographically, with the highest risk of critical conditions occurring in densely populated low‐income countriesThere is an urgent need to follow‐up the progress of treatments and to make adjustments whenever needed [ABSTRACT FROM AUTHOR]

This contribution applies the "mean temperature of the catch" (MTC) concept of Cheung et al. (Nature 497:365–368, 2013) to fish catch data for Lake Peipsi, Estonia/Russia, covering the years 1931 to 2019. The preferred temperature of each of the ten target fish species was obtained from the literature, and combined with the species-specific catch data to obtain MTC values for each year. The analysis of the MTC time series thus obtained with a segmented regression yielded two trend lines, one horizontal at 14.5 °C (1931–1986), and the other (1987–2019) ascending with a slope 0.85 °C·decade−1. Overall, the segmented regression model explains over half of the variance of the MTC data set (multiple R2 = 0.53; adjusted R2 = 0.51). Lake surface water temperatures correlate with MTC, even though weakly (r = 0.30), when considering a 2-year time lag. The fish community of the shallow Lake Peipsi reacts more strongly to temperature changes than marine ecosystems so far studied using the MTC. [ABSTRACT FROM AUTHOR]

Nutrient pollution causes frequent blooms of potentially harmful cyanobacteria in Lake Peipsi (Estonia/Russia). Although external nutrient loading has reduced since the 1990s, lake water quality has barely improved, and eutrophication is still considered a threat to lake biota and water usage. To understand the recovery dynamics of the lake it is necessary to analyse the effects of land use and lake management on water quality to develop mitigation strategies. Comprehensive analysis has thus far failed due to information gaps inherent to conventional monitoring strategies. We show how two large-scale hydrological models using Earth observation data provide spatial information on pollution and can help explain the causes of past and current lake eutrophication. WaterGAP3.2 provides valid estimates of present and probable future phosphorus concentration in the lake water, based on past hydrological conditions. WaterWorld models spatial potential water quality and a scenario of optimal pollution reduction. Remotely sensed optical water quality data can be used to analyse recent, spatial water quality dynamics. The spatial and temporal algae distributions and can help explain eutrophication causes at Lake Peipsi and its catchment, adding value to in situ monitoring and supporting river basin management with large scale data. [ABSTRACT FROM AUTHOR]

Climate change in recent decades has been identified as a significant threat to natural environments and human wellbeing. This is because some of the contemporary changes to climate are abrupt and result in persistent changes in the state of natural systems; so called regime shifts (RS). This study aimed to detect and analyse the timing and strength of RS in Estonian climate at the half-century scale (1966−2013). We demonstrate that the extensive winter warming of the Northern Hemisphere in the late 1980s was represented in atmospheric, terrestrial, freshwater and marine systems to an extent not observed before or after the event within the studied time series. In 1989, abiotic variables displayed statistically significant regime shifts in atmospheric, river and marine systems, but not in lake and bog systems. This was followed by regime shifts in the biotic time series of bogs and marine ecosystems in 1990. However, many biotic time series lacked regime shifts, or the shifts were uncoupled from large-scale atmospheric circulation. We suggest that the latter is possibly due to complex and temporally variable interactions between abiotic and biotic elements with ecosystem properties buffering biotic responses to climate change signals, as well as being affected by concurrent anthropogenic impacts on natural environments. [ABSTRACT FROM AUTHOR]

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Long-term datasets of nutrient levels provide a unique opportunity to study the changes that occur in lake ecosystems subjected to multiple man-induced and natural pressures. Unfortunately, the relevant dataset of thousands of records for Lake Peipsi (Estonia/Russia) is rather fragmentary and therefore difficult to analyse. Focusing on the total phosphorus concentration (TP), which is believed to be the main reason for degradation of the shallow lowland lake, we tailored, using SAS/STAT software, a special mixed regression model having 61 linear parameters and a repeated measures approach with spatial covariance structure. The model describes the dependence of TP in the surface water on year number (1985–2010), on the day of year and on geographical coordinates. Based on Akaike's criterion, the present model is superior to the analogous model, where the prediction errors (residuals) are supposed to be independent. Another advantage of the present model is that it distinguishes two groups of factors related to the variation in TP residuals. Factors of the first group affect TP synchronously within the larger areas, while this synchrony is weakening down to about 75 km or even more as has been shown by the SAS VARIOGRAM procedure. Factors in the other group can be associated with sampling instability and random errors in laboratory analyses. The influence of both factor groups on TP is approximately equal, with the related variance components on a log2-scale being 0.12 and 0.15. [ABSTRACT FROM PUBLISHER]

Pikeperch is a major predator in the pelagic zone of eutrophic waters, such as the large north-temperate lowland lakes Võrtsjärv (Estonia) and Peipsi (Estonia/Russia). The size and structure of the pikeperch population is strongly influenced by their success at the juvenile stage. Therefore, we investigated the diet and prey selection of pikeperch fry caught in the ice-free period in lakes Peipsi and Võrtsjärv in 2007 and 2008. We analysed the stomach contents of 635 pikeperch from Lake Peipsi and 202 pikeperch from Lake Võrtsjärv, and compared our findings with similar data from the 1950s (Erm, About Biological and Morphological Differences of Pikeperch. Hydrobiological Researches II (in Estonian), ). Analysing 4-20 cm long fry, we studied differences in prey size, seasonal diet patterns and the ontogenetic diet shift. In both lakes, 0+ pikeperch feed mostly on large predatory zooplankters. However, in Lake Peipsi the stomach content weight and the average number of food items in stomach were higher, and the food spectrum was wider than in Lake Võrtsjärv. There was also a difference in the type of food that dominated fry's stomach content (calculated by weight) in the two lakes. In Lake Peipsi, chironomids larvae, as well as zooplankters Daphnia galeata and Bythotrephes longimanus dominated, while in Lake Võrtsjärv zooplankters Mesocyclops leuckarti and Leptodora kindti. Seasonal analysis showed that cladocerans dominated in pikeperch fry stomach content in summer and at the beginning of September, but copepods were dominant in autumn and spring. In contrast to the studies carried out from 1952 to 1958 (Erm, About Biological and Morphological Differences of Pikeperch. Hydrobiological Researches II (in Estonian), ), the shift from planktivory to piscivory at the end of the first growing season was hardly ever observed during our investigation. We believe this is due to the lack of suitable prey fish as there was a collapse of the smelt, Osmerus eperlanus (L.), population in both lakes. The transition of pikeperch from planktivory to piscivory was delayed till the next summer. [ABSTRACT FROM AUTHOR]

We investigated changes in the spatial distribution of nitrogen (N) and phosphorus (P) in Lake Peipsi using limnological data from 1970 to 2005. The results show differences in nutrient content between the northern and southern parts of the lake (polarity) and indicate possible causes of eutrophication of this large international lake. The results show a steady gradient in total P (TP) and total N (TN) content along the lake: the northern and deepest part, Lake Peipsi s.s., is significantly less loaded with nutrients than the southern and very shallow part, Lake Pihkva, into which the main inflow, the Velikaya River, discharges. However, the long-term temporal patterns of N and P polarity are different. Statistical analysis, using a parametric functions technique in the framework of general linear analysis provided by the SAS procedures GLM and MIXED, revealed that the polarity of N compounds has been relatively stable over the years and can be related to differences in natural conditions between different parts of the lake. Our study indicates that Lake Peipsi is quite resistant to year-to-year changes in N load, and the in-lake N concentrations are quite stable on a long-term scale. In contrast, the increasing difference in P concentrations between the northern and southern parts of the lake clearly shows that the input of P from the south is increasing. Our results confirm that the anthropogenic input of P is the main reason for the deterioration of the Lake Peipsi ecosystem. [ABSTRACT FROM AUTHOR]

Data for the vegetation periods (May–November) of 1985–2003 were used to collate the nutrient content and biomass of the most important phytoplankton groups in Lake Peipsi (Estonia). Two periods differing in external nutrient load and water level were compared by analysis of variance. The years 1985–1988 were characterized by the highest loads of nitrogen and phosphorus, high water level and cool summers. The years 2000–2003 were distinguished by low or medium water levels and warm summers. The first period showed statistically significantly higher values of total nitrogen (Ntot) and a higher Ntot:Ptot mass ratio. The second period showed a higher content of total phosphorus (Ptot), a higher ratio of dissolved inorganic compounds N to P and higher phytoplankton and cyanobacterial biomasses. Comparison between parts of the lake demonstrated that the differences between the two periods were more evident in the shallower and strongly eutrophic parts, Lake Pihkva and Lake Lämmijärv, than in the largest and deepest part, the moderately eutrophic Lake Peipsi s.s. Temperature and water level acted synergistically and evidently influenced phytoplankton via nutrients, promoting internal loading when the water level was low and the temperature high. The effect of water level was stronger in the shallowest part, Lake Pihkva. The difference in Ptot content between the southern and northern parts was twofold; the Ntot:Ptot mass ratio was significantly lower in the southern parts, and phytoplankton biomass (particularly the biomass of cyanobacteria) was significantly higher for Lake Pihkva and Lake Lämmijärv than for Lake Peipsi s.s. [ABSTRACT FROM AUTHOR]

A self-organising map (SOM) was applied to extract long-term dynamic patterns of fish community in shallow eutrophic Lake Peipsi using the commercial fishery statistics recorded for 64 years from 1931 to 2002 (excluding 1940–1949 due to the World War II). In the dataset of fishery statistics, mainly 11 taxa were recognised according to their commercial importance. Therefore, we used the dataset consisting of 64 sample units (i.e., year) with 11 taxa for patterning the fish community by the SOM. Our results suggest that the fish community of Lake Peipsi was mostly gradually changed in long-term scale, but some abrupt changes were also noticeable. Despite the same species composition, the total annual catch has declined indicating changes of fish community. The fish community of Lake Peipsi has shifted in long-term scale from clean-and cold-water species like vendace Coregonus albula (L. ), whitefish C. Lavaretus L. And burbot Lota lota (L. ) to more pikeperch Sander lucioperca (L. ) preferring productive warm and turbid waters. Both, the deterioration of aquatic environment and predatory effect of pikeperch prevent recovery of vendace population. Gradual reduction of the stock of smelt Osmerus eperlanus L. Is also a sign of ongoing eutrophication, while its disappearance from catches for 3 years (1973–1975) was the result of summer fish-kill. The effect of fishing is the most important human impact on the fish community in Lake Peipsi. Extensive use of fine-meshed towed fishing gear (e.g., trawls replaced later by bottom seines) affected mostly recruitment of pelagic predator, pikeperch, killing young specimens of this fish in large quantities. Even though the fishery methods have changed, the fish stocks of the lake have repeatedly suffered from the over-fishing. [Copyright &y& Elsevier]

1. This synthesis examines 35 long-term (5–35 years, mean: 16 years) lake re-oligotrophication studies. It covers lakes ranging from shallow (mean depth <5 m and/or polymictic) to deep (mean depth up to 177 m), oligotrophic to hypertrophic (summer mean total phosphorus concentration from 7.5 to 3500 μg L−1 before loading reduction), subtropical to temperate (latitude: 28–65°), and lowland to upland (altitude: 0–481 m). Shallow north-temperate lakes were most abundant. 2. Reduction of external total phosphorus (TP) loading resulted in lower in-lake TP concentration, lower chlorophyll a (chl a) concentration and higher Secchi depth in most lakes. Internal loading delayed the recovery, but in most lakes a new equilibrium for TP was reached after 10–15 years, which was only marginally influenced by the hydraulic retention time of the lakes. With decreasing TP concentration, the concentration of soluble reactive phosphorus (SRP) also declined substantially. 3. Decreases (if any) in total nitrogen (TN) loading were lower than for TP in most lakes. As a result, the TN : TP ratio in lake water increased in 80% of the lakes. In lakes where the TN loading was reduced, the annual mean in-lake TN concentration responded rapidly. Concentrations largely followed predictions derived from an empirical model developed earlier for Danish lakes, which includes external TN loading, hydraulic retention time and mean depth as explanatory variables. 4. Phytoplankton clearly responded to reduced nutrient loading, mainly reflecting declining TP concentrations. Declines in phytoplankton biomass were accompanied by shifts in community structure. In deep lakes, chrysophytes and dinophytes assumed greater importance at the expense of cyanobacteria. Diatoms, cryptophytes and chrysophytes became more dominant in shallow lakes, while no significant change was seen for cyanobacteria. 5. The observed declines in phytoplankton biomass and chl a may have been further augmented by enhanced zooplankton grazing, as indicated by increases in the zooplankton : phytoplankton biomass ratio and declines in the chl a : TP ratio at a summer mean TP concentration of <100–150 μg L−1. This effect was strongest in shallow lakes. This implies potentially higher rates of zooplankton grazing and may be ascribed to the observed large changes in fish community structure and biomass with decreasing TP contribution. In 82% of the lakes for which data on fish are available, fish biomass declined with TP. The percentage of piscivores increased in 80% of those lakes and often a shift occurred towards dominance by fish species characteristic of less eutrophic waters. 6. Data on macrophytes were available only for a small subsample of lakes. In several of those lakes, abundance, coverage, plant volume inhabited or depth distribution of submerged macrophytes increased during oligotrophication, but in others no changes were observed despite greater water clarity. 7. Recovery of lakes after nutrient loading reduction may be confounded by concomitant environmental changes such as global warming. However, effects of global change are likely to run counter to reductions in nutrient loading rather than reinforcing re-oligotrophication. [ABSTRACT FROM AUTHOR]

In Lake Peipsi (3550 km², mean depth 7.1 m) sporadic fish kills have been registered repeatedly since 1959 during cyanobacterial blooms in warm summers. At the time of the excessive fish kill in August 2002 comprehensive investigations of phytoplankton abundance, key physical and chemical parameters of lake water (including diurnal fluctuations of the dissolved oxygen and ammonium ion concentrations and pH) as well as species composition and number of dead fish were carried out along the Estonian shore. The aim of the study was to assess how many fish were killed and to determine ecological conditions in the lake that led to the fish kill. The results suggest that the fish kill was induced by the synergistic effect of several unfavourable conditions, which appeared in the lake during the strong bloom of the cyanobacterium Gloeotrichia echinulata accompanied with continuous hot weather and decreasing water level. A combination of factors such as high water temperature (up to 26°C), low water level (70 cm below the long-term average), great spatial and diurnal variations in the dissolved oxygen (saturation 25-165%) and ammonium ion (up to 0.33 mg NL-1) concentrations as well as in the pH (7.7-9.5) were responsible for the mass mortality of fish. The influence of cyanotoxins on the condition of fish cannot be neglected either. Ruffe, a bottom dwelling fish, suffered the most severely. [ABSTRACT FROM AUTHOR]

Ruffe is one of the most numerous fishes in Estonian large Lakes Peipsi (area 3555 km2, mean depth 7.1 m) and Võrtsjärv (270 km2, 2.8 m). Owing to its small size ruffe has little value for commercial or recreational fisheries today. However, due to their high abundance, ruffe play an important role in the food webs of both lakes. The aim of the investigation was to establish the proportion of ruffe in the fish community and to assess the wellbeing of this fish in the two lakes on the basis of growth rate and condition factor. According to experimental catches made in autumn 1998–2002, the average total catch of fishes per trawl-hour (CPUE) in L. Peipsi was about two times higher than in L. Võrtsjärv (204 kg and 105 kg, respectively). CPUE of ruffe made up 16 kg in L. Peipsi and 7 kg in L. Võrtsjärv. In these lakes the fish community composition and food resource appear to be different. Benthivorous fishes were dominating in L. Võrtsjärv and the biomass of macrozoobenthos was significantly lower in this lake than in L. Peipsi. In the first year, the growth rate of ruffe was higher in L. Peipsi where the state of zooplankton was better compared with L. Võrtsjärv. Differences in the linear growth rate of older fishes in L. Peipsi and L. Võrtsjärv were not significant. The lower condition factor of ruffe in L. Võrtsjärv reflects the limited food resource of abundant benthivorous fishes in this lake. Different trophic relationships in Estonian large lakes are better reflected in the ruffe's condition factor than in its linear growth rate. [ABSTRACT FROM AUTHOR]

The population dynamics of fish in northern lakes is strongly influenced by climatic factors. In this study, we investigated whether there is a link between the late 1980s climate regime shift in Europe and the collapse of vendace (Coregonus albula) population at the same time in Lake Peipsi. Until the end of the 1980s, vendace was very abundant in the lake, but then its catches sharply declined. This decline inspired investigations into the extreme weather events preceding the vendace collapse using data on daily water temperatures and ice phenology together with commercial fishery statistics since 1931 and test catch data since 1986. We identified using advanced statistical methods that the hot summer of 1988, which was accompanied by a severe cyanobacterial bloom and extensive fish kill, and the subsequent non-permanent ice cover and early ice-offs in 1989 and 1990 in Lake Peipsi were the main reasons for the disappearance of vendace from catches in 1991. Moreover, a negative correlation appeared between catches of the predatory pikeperch (Sander lucioperca) and vendace. Predation pressure as well as fish habitat degradation caused by lake eutrophication may contribute to the instability of the vendace population too. Our study showed that extreme weather events such as heat waves in summer and non-permanent ice-cover in winter in consecutive years may have long-lasting harmful effects on the population abundance of cool-water fish species such as vendace whose eggs usually develop under an ice cover in north-temperate lakes. [ABSTRACT FROM AUTHOR]

Changes in the ice phenology, seasonal temperature and extreme events are consistent evidence of climate change effect on lakes. In this study, we analyzed multiannual variability, determined long-term trends and detected changes in the frequency of extreme events in the surface water temperature (LSWT) of Lake Peipsi (Estonia/Russia) for nearly seven decades (1950-2018) and aimed to trace how the LSWT responded to the climate change. Dynamic water temperature parameters were calculated using the smoothed water temperature curve fitted to daily water temperatures. Our results showed that, although the average LSWT did not increase significantly on an annual basis since 1950 it rose rapidly in the winter season during the last decade (∼ +0.5 °C). Ice formation exhibited a marked (∼15 days) delay since 2007 resulting in a longer open water period. Extreme LSWT events did not occur more frequently. We noticed however significant fluctuating in winter LSWT in time series, starting from 2007 and also causing an increase in stochasticity. The consequences of the on-going winter warming and changes of ice cover phenology are expected to be crucial for Lake Peipsi ecosystem functioning and impact on lake biota, especially temperature-sensitive native fishes. [ABSTRACT FROM AUTHOR]

Abstract: Over the last 3–4 decades, Lake Peipsi water (sampling site A, middle part of the lake, and site B, northern part) has experienced a statistically significant increase of bicarbonate, pH, chemical oxygen demand, nitrate (and nitrite in site B), due to combination of climate change and eutrophication. By photochemical modelling, we predicted a statistically significant decrease of radicals OH and (site A, by 45% and 35%, respectively) and an increase of triplet states of chromophoric dissolved organic matter (3CDOM∗; site B, by ∼25%). These species are involved in pollutant degradation, but formation of harmful by-products is more likely with 3CDOM∗ than with OH. Therefore, the photochemical self-cleansing ability of Lake Peipsi probably decreased with time, due to combined effects of climate change and eutrophication. In different environments (e.g. Lake Maggiore, NW Italy), ecosystem restoration policies had the additional advantage of enhancing sunlight-driven detoxification, suggesting that photochemical self-cleansing would be positively correlated with lake water quality. [Copyright &y& Elsevier]