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Deep lakes are critical for freshwater storage, yet they are struggling against major ecological issues from climate change and nutrient pollution. A comprehensive understanding of internal feedback mechanisms is crucial for regulating nutrients in these lakes. A five‐year study was conducted on the diatom community and environment in Lake Fuxian, China's largest deep freshwater lake, which is becoming eutrophic. The results indicate a shift in the diatom community from a stable state dominated by a single species to a rapid seasonal fluctuation, and there is a significant increase in diatom biomass. Specifically, stable stratification and low nutrient concentrations are limiting the growth of diatom biomass and maintaining the dominance of Cyclotella. Nutrients in the hypolimnion were replenished in the epilimnion during the extreme cold of winter, triggering a shift in the diatom community. This shift may imply that future climate change will exacerbate the positive feedback of hypoxia‐nutrient release of algal blooms, potentially triggering a regime shift in the ecosystem of the entire lake. This study underscores the fact that climate change alters the internal feedback mechanisms of deep lakes, reducing ecosystem stability, and provides a scientific basis for further clarification of protection measures for deep lakes. [ABSTRACT FROM AUTHOR]

Microbial functional composition is important for biogeochemical cycles, and is usually constrained by taxonomic species pool and natural environmental gradients. However, the distribution of functional genes in deep lakes and the driving factors remains elusive. Here, we quantified the abundance of 71 functional genes relevant to carbon degradation, carbon fixation, methane metabolism, nitrogen cycling, phosphorus cycling, and sulfur cycling in 38 sediments along the water depth ranging from 0 to 90 m in Lugu Lake, China, using Quantitative Microbial Ecology Chip (QMEC) and then explored their water-depth diversity pattern and abiotic and biotic drivers. Functional gene diversity showed a hump-shaped pattern along the depth and peaked at around 50 m which is the low boundary of thermocline layer. There were specific environmental preferences among functional gene subgroups such as nitrogen and sulfur cycling genes preferring to deeper and shallow waters, respectively. The dissimilarity of total functional genes increased with water depth distance indicating a distance-decay relationship. There was a congruence between functional and taxonomic composition by showing the positive correlations between the compositions of functional genes and bacteria or archaea. This phenomenon is consistently observed for the six functional gene subgroups, and the congruence strength was highest for nitrogen cycling while lowest for sulfur cycling. Compared to abiotic factors, biotic factors were more relevant to the functional gene diversity and composition. Biotic factors explained 28.5 % of the variance of functional gene diversity, while water depth and other environmental factors such as water total phosphorus and sediment carbon explained 4.2 % and 3.8 %, respectively. For functional gene composition, biotic factors accounted for 25.2 % of the variance, whereas water depth and other environmental factors contributed to 0.7 % and 4.4 %, respectively. Among all explanatory variables for function genes, bacterial composition had the highest contribution, which was further supported by showing its direct effects of 1.45 and 0.86 on functional diversity and composition, respectively. This study for the first time quantified the microbial functional genes along water depth in deep lakes and provided a more comprehensive understanding of the functional dynamics in microbial communities within aquatic ecosystems.

Abstract Deep lakes are critical for freshwater storage, yet they are struggling against major ecological issues from climate change and nutrient pollution. A comprehensive understanding of internal feedback mechanisms is crucial for regulating nutrients in these lakes. A five‐year study was conducted on the diatom community and environment in Lake Fuxian, China's largest deep freshwater lake, which is becoming eutrophic. The results indicate a shift in the diatom community from a stable state dominated by a single species to a rapid seasonal fluctuation, and there is a significant increase in diatom biomass. Specifically, stable stratification and low nutrient concentrations are limiting the growth of diatom biomass and maintaining the dominance of Cyclotella. Nutrients in the hypolimnion were replenished in the epilimnion during the extreme cold of winter, triggering a shift in the diatom community. This shift may imply that future climate change will exacerbate the positive feedback of hypoxia‐nutrient release of algal blooms, potentially triggering a regime shift in the ecosystem of the entire lake. This study underscores the fact that climate change alters the internal feedback mechanisms of deep lakes, reducing ecosystem stability, and provides a scientific basis for further clarification of protection measures for deep lakes.

A thermal system in the very deep Lake Tazawa (maximum depth, 423 m) was investigated by estimating the heat budget. In the heat budget estimate, the net heat input at the lake's surface and the heat input by river inflow and groundwater inflow were considered. Then, the heat loss by snowfall onto the lake's surface was taken into account. Meanwhile, the lake water temperature was monitored at 0.2 m to the bottom by mooring temperature loggers for more than two years. The heat storage change of the lake from the loggers was calibrated by frequent vertical measurements of water temperature at every 0.1 m pitch by a profiler with high accuracy (±0.01 °C). The heat storage change (W/m2) obtained by the temperature loggers reasonably accorded to that from the heat budget estimate. In the heat budget, the net heat input at lake surface dominated the heat storage change, but significant heat loss by river inflow sporadically occurred, caused by the relatively large discharge from a reservoir in the upper region. How deeply the vertical water circulation in the lake occurs in winter was judged according to the differences between water temperatures at 0.2 m depth and at the bottom and between vertical profiles of dissolved oxygen over winter. It is strongly suggested that the whole water circulation process does not occur every winter, and if it does, it is very weak. A consistent increase in the water temperature at the bottom is probably due to the conservation of geothermal heat by high frequency of incomplete vertical water circulation. [ABSTRACT FROM AUTHOR]

In March 2019, we studied the taxonomic composition, vertical and horizontal distribution of under-ice zooplankton in Lake Pleshcheyevo and revealed that its quantity (abundance 11.5–13.8 thous.ind./m3, biomass

A thermal system in the very deep Lake Tazawa (maximum depth, 423 m) was investigated by estimating the heat budget. In the heat budget estimate, the net heat input at the lake’s surface and the heat input by river inflow and groundwater inflow were considered. Then, the heat loss by snowfall onto the lake’s surface was taken into account. Meanwhile, the lake water temperature was monitored at 0.2 m to the bottom by mooring temperature loggers for more than two years. The heat storage change of the lake from the loggers was calibrated by frequent vertical measurements of water temperature at every 0.1 m pitch by a profiler with high accuracy (±0.01 °C). The heat storage change (W/m2) obtained by the temperature loggers reasonably accorded to that from the heat budget estimate. In the heat budget, the net heat input at lake surface dominated the heat storage change, but significant heat loss by river inflow sporadically occurred, caused by the relatively large discharge from a reservoir in the upper region. How deeply the vertical water circulation in the lake occurs in winter was judged according to the differences between water temperatures at 0.2 m depth and at the bottom and between vertical profiles of dissolved oxygen over winter. It is strongly suggested that the whole water circulation process does not occur every winter, and if it does, it is very weak. A consistent increase in the water temperature at the bottom is probably due to the conservation of geothermal heat by high frequency of incomplete vertical water circulation.

The spatial distribution of 39 species of Chydoridae, representing seven families, was examined in a stratified Palaearctic lake in Poland (Lake Piaseczno). Thirty-one of the species living in that lake were found to exist exclusively in the littoral zone. No species were found exclusively in the pelagic zone; in this zone, eight species were identified, but all of these were also quite abundant in the littoral zone. Almost all species of Chydoridae and all species of Macrothricidae were found only in littoral, whereas Daphnidae and Sididae families comprised species either restricted to the littoral or occurring in both pelagic and littoral zones. Two Bosminidae species, in turn, displayed quite a consistent distribution in both biotic zones, but differed in their habitat preferences. On the other hand, species of Polyphemidae and Leptodoridae exhibited littoral and littoral-pelagic distributions, respectively. Few species occurred in one habitat only. Most species, despite showing clear preferences for a distinct habitat (or habitats), were also present at lower densities throughout the littoral zone, or the whole lake, in the case of limnetic species. Archetype analysis showed that cladocerans were distributed along the entire gradient of macrophyte characteristics and habitat depth. Among Chydoridae, which displayed the strongest attachment to habitats overgrown by macrophytes, few species showed above 50% similarity to the archetype representing species living among submerged macrophytes with the highest plant per volume infested. Furthermore, many littoral species, including these of the Macrothricidae family, P. pediculus and S. mucronata, avoided staying in habitats with particularly complicated spatial architecture. Regarding their distribution in relation to depth, cladocerans could be grouped into species found in the whole littoral zone, species settling in relatively shallow parts of the littoral zone, species found mainly in habitats 3–6 m deep and species settling throughout the lake. Archetype analysis showed negligible similarity between cladocerans and the archetype representing species living in macrophyte-free habitats in the deepest parts of the lake. The study provides quantitative support showing that cladocerans display a distribution threshold at one time in one lake. Although this group of aquatic invertebrates is widely suspected of being ecologically flexible and tolerant to environmental gradients, individual species showed high spatial segregation according to depth and habitat architecture. [ABSTRACT FROM AUTHOR]

Deep lakes under climate change are experiencing reduced deep mixing, with a consequent increase in nutrients concentration and oxygen deficit in the hypolimnion. From this perspective, greater efforts should be made to reduce the phosphorus load delivered to these lakes by their tributaries. An essential precondition for this action is a reliable estimate of the loads, which is challenging due to the marked temporal variability of the hydrologically‐driven diffuse sources. In this article, we used a high‐resolution phosphorus time series measured at the mouth of the main tributary of Lake Iseo and a machine learning algorithm to show the dominant role played by the acute, storm‐dependent transport. The results emphasize the need to control loads strictly linked to precipitation and runoff in the drained watershed, representing 31% of the observed events but responsible for 64% of the overall load to the lake. We also proved evidence that the current obligations on nutrients monitoring miss the total phosphorus dynamics, leading to a systematic underestimation of the load conveyed by the inflows. Accordingly, we propose a sampling methodology where the timing and the methods for data interpolation are established according to the hydrological conditions in the drained watershed. Accounting for the economical and practical constraints imposed by the monitoring authorities, we propose to integrate, at the mouth of lake tributaries, a monthly manual sampling with an auto‐sampler programmed to fill 2 bottles in correspondence of each high flow event. Our simulations showed that in this case the load estimation error was reduced below 1%, implying, on average, 13 field surveys/year and 21 laboratory analyses/year only. It is reasonable to expect comparable performances in hydrologically similar watersheds. [ABSTRACT FROM AUTHOR]

[Display omitted] • Functional gene diversity showed a hump-shaped pattern along the water depth gradient. • Specific environmental preferences existed among subgroups of functional genes. • Functional gene composition increased with depth change. • Functional gene composition was positively correlated with microbial composition. • Biotic factors explained more variance in microbial functional gene diversity. Microbial functional composition is important for biogeochemical cycles, and is usually constrained by taxonomic species pool and natural environmental gradients. However, the distribution of functional genes in deep lakes and the driving factors remains elusive. Here, we quantified the abundance of 71 functional genes relevant to carbon degradation, carbon fixation, methane metabolism, nitrogen cycling, phosphorus cycling, and sulfur cycling in 38 sediments along the water depth ranging from 0 to 90 m in Lugu Lake, China, using Quantitative Microbial Ecology Chip (QMEC) and then explored their water-depth diversity pattern and abiotic and biotic drivers. Functional gene diversity showed a hump-shaped pattern along the depth and peaked at around 50 m which is the low boundary of thermocline layer. There were specific environmental preferences among functional gene subgroups such as nitrogen and sulfur cycling genes preferring to deeper and shallow waters, respectively. The dissimilarity of total functional genes increased with water depth distance indicating a distance-decay relationship. There was a congruence between functional and taxonomic composition by showing the positive correlations between the compositions of functional genes and bacteria or archaea. This phenomenon is consistently observed for the six functional gene subgroups, and the congruence strength was highest for nitrogen cycling while lowest for sulfur cycling. Compared to abiotic factors, biotic factors were more relevant to the functional gene diversity and composition. Biotic factors explained 28.5 % of the variance of functional gene diversity, while water depth and other environmental factors such as water total phosphorus and sediment carbon explained 4.2 % and 3.8 %, respectively. For functional gene composition, biotic factors accounted for 25.2 % of the variance, whereas water depth and other environmental factors contributed to 0.7 % and 4.4 %, respectively. Among all explanatory variables for function genes, bacterial composition had the highest contribution, which was further supported by showing its direct effects of 1.45 and 0.86 on functional diversity and composition, respectively. This study for the first time quantified the microbial functional genes along water depth in deep lakes and provided a more comprehensive understanding of the functional dynamics in microbial communities within aquatic ecosystems. [ABSTRACT FROM AUTHOR]

The study presents changes in the elements of the hydrological regime of Lake Hańcza in the period 1960–2019, including water temperature, ice cover characteristics and water level. It was determined that statistically significant changes resulted in an increase in water temperature (0.11°C·dec−1), a decrease in maximum ice thickness (5 cm·dec−1) and an increase in water levels (6.7 cm·dec−1). Changes in water temperature and ice cover in the analysed case are different from those in other lakes of the region. As the tests conducted in this study and in previous research have shown, the lake has resisted global warming for a relatively long time, and the change in thermal conditions occurred a decade later than in other lakes in this part of Europe. The analysed case leads to the conclusion that the morphometric features of lakes significantly modify the influence of overriding factors, such as climate conditions. [ABSTRACT FROM AUTHOR]

We review the state of the art of limnological studies in Lake Iseo and provide updated data concerning long-term investigations (from 1993 to 2018) carried out on chemical and physical parameters (e.g., oxygen, phosphorus, silicon). Changes observed in Lake Iseo were compared with those reported in other Deep South alpine Lakes (DSLs) to highlight analogies and differences of long-term chemical, physical, and biological patterns. Until the 1960s, Lake Iseo and other DSLs were oligotrophic. The increase of anthropogenic pressure and global warming has led to a progressive and unrecovered process of eutrophication. Moreover, the decrease in frequency of full mixing episodes has induced a state of temporary meromixis. Other changes have been identified over the last two decades, especially concerning the phytoplankton and zooplankton communities, and new emerging chemical pollutants were detected. Given the important ecological and socioeconomic role of Lake Iseo, long-term investigations are of paramount importance to understand the response of the lake ecosystem to climatic and anthropogenic stressors. These two factors can also act coupled with new combined and synergic effects.

We review the state of the art of limnological studies in Lake Iseo and provide updated data concerning long-term investigations (from 1993 to 2018) carried out on chemical and physical parameters (e.g., oxygen, phosphorus, silicon). Changes observed in Lake Iseo were compared with those reported in other Deep South alpine Lakes (DSLs) to highlight analogies and differences of long-term chemical, physical, and biological patterns. Until the 1960s, Lake Iseo and other DSLs were oligotrophic. The increase of anthropogenic pressure and global warming has led to a progressive and unrecovered process of eutrophication. Moreover, the decrease in frequency of full mixing episodes has induced a state of temporary meromixis. Other changes have been identified over the last two decades, especially concerning the phytoplankton and zooplankton communities, and new emerging chemical pollutants were detected. Given the important ecological and socioeconomic role of Lake Iseo, long-term investigations are of paramount importance to understand the response of the lake ecosystem to climatic and anthropogenic stressors. These two factors can also act coupled with new combined and synergic effects. [ABSTRACT FROM AUTHOR]

Highlights • PCLake+ is an extended version of the lake water quality model PCLake. • PCLake+ is improved with respect to stratification and climate-related processes. • In the development of PCLake+ we embraced the philosophy of the PCModel family. • PCLake+ complies well with limnological knowledge. • PCLake+ holds promise for future application to lakes around the globe. Abstract The lake ecosystem model PCLake is a process-based model that was developed to simulate water quality based on ecological interactions in shallow, non-stratifying lakes in the temperate climate zone. Here we present PCLake+, which extends the PCLake model to cover a wide range of freshwater lakes that differ in stratification regime and climate-related processes. To this end, the model was extended with a hypolimnion layer that can be invoked and configured by forcing functions or by simple built-in empirical relationships that impose stratification. Further adjustments to the original PCLake model have been made with respect to the calculation of 1) light irradiation in the water column, 2) evaporation processes and 3) phenology of macrophytes. The simulation output of PCLake+ for different types of lakes complies well with generally accepted limnological knowledge, thus holding promise for future contributions to ecological theory and application to lakes around the globe. [ABSTRACT FROM AUTHOR]

The aim of this study was to develop faecal pollution model structures with artificial neural networks (ANNs) for cost-effective lake water quality management studies. In this study 5 artificial neural networks model structures were applied to predict the Faecal coliform concentrations for 4 different coast areas "Göllüce, İnciraltı, Darka, Orhangazi" and all data of the coasts in Lake İznik- Turkey. The Levenberg-Marquardt and backpropagation algorithm was proposed for feed-forward neural networks training. According to performance functions root mean squared error (RMSE), neural network model structures provided acceptable results. Correlation values (R) were found between 0.590 and 0.999. Increasing the number of hidden layer in the model structures was not raised the model efficiency in each trial. Type and number of input parameters were more effective for some model efficiency. Increasing the number of hidden layer and inputs in the model structures did not raise the model efficiency in each trial. Because depending on the numbers and chemical compositions of the substrates in the lake water microorganism's metabolism and their growth rates could be influenced differently and the larger error values of the modeling results determined in Göllüce and Orhangazi Coasts which influenced by pollution sources. Water quality modeling studies and increasing of monitoring would provide more productive results for protection and management of coastal. [ABSTRACT FROM AUTHOR]

In Lake Iseo (Lombardia, Italy), the predominant species in the cyanobacterial taxa was Planktothrix rubescens. However, since 2014, the presence of an allochthonous Cyanobacteria, Tychonema bourrellyi, able to produce consistent biomasses and harmful toxins, was detected. The causes of this expansion are poorly understood. Many studies have linked the development of allochthonous Cyanobacteria populations with climate change. This study shows the spatio-temporal dynamics, the ecological requirements, and the interspecific relationship of P. rubescens and T. bourrellyi. Samples were collected monthly in 2016 at six different depths in the water column; 20 chemico-physical characteristics were measured; and Cyanobacteria density, morphology, and biovolume were evaluated. The results allowed a comparison of the spatial pattern of the two species, which showed a greater distribution at a depth of 10-20 m, and their seasonal dynamics. Both Cyanobacteria were present throughout the year, with the greatest abundance during the period from March to May. A temporal shift was observed in their development, linked to different capacities for overcoming winter and mixing periods. Principal Component Analysis, performed on 20 observations (4 months × 5 depths), highlighted the important role of the stability of the water column in determining T. bourrellyi settlement in Lake Iseo and the role of solar radiation in spring population development. [ABSTRACT FROM AUTHOR]

Monitoring during three meteorologically different spring seasons in 2012, 2013, and 2014 revealed that temperature increase in spring, which influences spring lake mixing duration, markedly affected nutrient availability and diatom deposition in a sediment trap close to the bottom of deep Tiefer See, NE Germany. Deposition of Stephanodiscus taxa and small Cyclotella taxa was much higher after late ice out and a deep, short lake mixing period in spring 2013, compared to that after gradual warming and lengthy lake mixing periods in spring 2012 and 2014, when only brief or marginal ice cover occurred. Availability of dissolved Si and P was 33 and 20 % higher, respectively, in 2013 compared to 2014. The observed relation between high (low) diatom deposition and short (lengthy) mixing duration in spring was applied to varved sediments deposited between AD 1924 and 2008. Low detrital Si content in trapped material and a sediment core enabled use of µXRF-counts of Si as a proxy for diatom silica. The spring mixing duration for 1951-2008 was derived from FLake-model calculations. The spring warming duration related to lake mixing was approximated from air temperatures for 1924-2008 using the dates when daily mean air temperature exceeded 5 °C (start) and 10 °C (end). Diatom silica deposition showed a significant ( p < 0.0001) inverse linear relationship with the modeled spring mixing duration (R = 0.36) and the spring warming duration (R = 0.28). In both cases, the relationship is strengthened when data from the period of low diatom production (1987-2005) is excluded (R = 0.59 and R = 0.35). Part of this low diatom production is related to external nutrient supply that favored growth of cyanobacteria at the expense of diatoms. This approach shows that diatom Si deposition was strongly influenced by the availability of light and nutrients, related to the duration of lake mixing and warming in spring, during most of the studied period. The remaining unexplained variability, however, indicates that additional factors influence Si deposition. Further tests in other deep, temperate lakes are necessary to verify if this relation is a common feature and consequently, if diatom Si can be used as a proxy for spring mixing duration in such lakes. [ABSTRACT FROM AUTHOR]

In-situ monitoring of lake water quality in synergy with satellite remote sensing represents the latest scientific trend in many water quality monitoring programs worldwide. This study investigated the suitability of the Operational Land Imager (OLI) instrument onboard the Landsat 8 satellite platform in accurately estimating key water quality parameters such as chlorophyll-a and nutrient concentrations. As a case study the largest freshwater body of Greece (Trichonis Lake) was used. Two Landsat 8 images covering the study site were acquired on 30 October 2013 and 30 August 2014 respectively. Near concurrent in-situ observations from two water sampling campaigns were also acquired from 22 stations across the lake under study. In-situ measurements (nutrients and chlorophyll-a concentrations) were statistically correlated with various spectral band combinations derived from the Landsat imagery of year 2014. Subsequently, the most statistically promising predictive models were applied to the satellite image of 2013 and validation was conducted using in-situ data of 2013 as reference. Results showed a relatively variable statistical relationship between the in-situ and reflectances (R logchl-a: 0.58, R NH4+: 0.26, R chl-a: 0.44). Correlation coefficient (R) values reported of up to 0.7 for ammonium concentrations and also up to 0.5 and up to 0.4 for chl-a concentration and chl-a concentrations respectively. These results represent a higher accuracy of Landsat 8 in comparison to its predecessors in the Landsat satellites series, as evidenced in the literature. Our findings suggest that Landsat 8 has a promising capability in estimating water quality components in an oligotrophic freshwater body characterized by a complete absence of any quantitative, temporal and spatial variance, as is the case of Trichonis lake. Yet, even with the presence of a lot of ground information as was the case in our study, a quantitatively accurate estimation of water quality constituents in coastal/inland waters remains a great challenge. The launch of sophisticated spaceborne sensing systems, such as that of Landsat 8, can assist in improving our ability to estimate freshwater lake properties from space.

• IsoGDGTs in the Lake Fuxian are primarily produced by Group I.1a Thaumarchaeota. • DO concentrations strongly affect the TEX 86 signal in the water column. • The warm-biased TEX 86 signal can be identified by % isoGDGT-2 with a threshold > 45%. The TEX 86 (tetraether index of 86 carbon atoms) temperature proxy has been widely applied to marine settings. The application of TEX 86 in lakes, however, is more complicated, as many other factors, such as dissolved oxygen (DO), also appear to influence the lacustrine TEX 86 signal. In order to better understand how DO content affects TEX 86 , we analyzed an annual cycle of isoGDGT distributions and abundances in the water column (0–100 m) of Lake Fuxian, in southwest China. It appears that isoGDGTs in suspended particulate matter (SPM) of the water column are mainly produced by aquatic Group I.1a Thaumarchaeota. The peak concentration of total isoGDGTs occurs mainly in June and December, which is probably driven by release of nutrients during phytoplankton blooms with a lag of about one month. About 95% of isoGDGTs occurred in the bottom water layer (hypolimnion) of this thermally stratified lake, indicating that Thaumarchaeota prefer to live in suboxic water conditions in Lake Fuxian. IsoGDGT-2 is the most sensitive component to monthly variations in DO contents. This relationship leads to a similar negative correlation between TEX 86 and DO. When TEX 86 values, especially at the hypolimnion, are lower than anticipated, this is caused by %isoGDGT-2 falling below 45%. Conversely, a warm bias of TEX 86 arising from a %isoGDGT-2 greater than 45% appears to be associated with lower DO contents. Therefore, this threshold of %isoGDGT-2 could be used in future paleoclimate reconstructions (of Lake Fuxian, and possibly similar lakes), especially since Thaumarchaeota typically reside at suboxic water layers. [ABSTRACT FROM AUTHOR]

The distribution of benthic macroinvertebrates was studied in deep Lake Motosu (oligotrophic lake), Japan. Bathymetrical sampling surveys were carried out using a standard Ekman grab at each of 16 stations in the lake on 8 March 2013. The average densities of the benthic community for all the stations were 2185 ind./m2, comprised principally of Tubifex tubifex (Müller) 23.4%, Asellus hilgendorfi Bovallius 4.9% and chironomids 65.8%. T. tubifex and chironomids inhabited the entire lake bottom, with higher densities in the shallower region (25 m>) than in the deeper region (ca. 120 m). On the other hand, the density of A. hilgendorfi increased with water depth and was highest in the deeper regions (>70 m). The densities of chironomid larvae were lower in the deeper region, with fewer chironomid larvae located in the center of the lake (637 ind./m2). The most abundant species, Micropsectra yunoprima Sasa, exhibited the widest distribution from 10.0 m to 121.0 m (mean density 926 ind./m2), followed by Procladius choreusi (Meigen) from 10 m to 74.1 m (mean density 365 ind./m2). The results of this study were compared to previous data by Kitagawa (1973) on chironomid larvae. The densities of these chironomid larvae increased throughout the whole lake in 2013. The water quality has not undergone a major change since the 1970's. In this study, the number of M. yunoprima larvae has shown a tendency to increase, especially in shallower regions; where they are widely distributed, suggesting the continuation of favorable bottom condition for larvae since the 1970's. [ABSTRACT FROM AUTHOR]

Abstract: Eutrophication has been a major stressor in lakes during the last century, with important implications for fish populations and thus fisheries. We summarised the Arctic charr (Salvelinus alpinus) fishery data available in Lake Geneva between 1887 and 2011 to describe contemporary catches in a broad perspective in relationship to the trophic status and the stocking history. Actual catches are low, but such levels had already been reached before the period of eutrophication. In addition, the high catch levels during the 1990s appeared to be artificially boosted by intense stocking and therefore cannot be used as a reference point. Thus, fishery data only do not allow for population functionality inference. Subsequently, we evaluated the contemporary contribution of stocking to catches and to the spawners by marking all of the fingerlings stocked in 2007 (n =993,300 individuals) with a mass marking otolith technique using alizarine Red S. Multiple markings allowed us to distinguish between three stocking practices and to compare their relative efficiency. From 2009 to 2011, 1929 charr were sampled in recreational catches, commercial catches, and in spawners. More than 51% (980) of the total sample set corresponded to the 2007 cohort. The total contribution of stocked fish was 84% at stage 2+, 72% at stage 3+, and 44% at stage 4+. The results were similar to prior values obtained during the 1980s. Differences in the contributions between the types of samples (commercial catches, recreational catches, and spawners) were found. The results highlighted the fact that the current stocking effectiveness was 4 to 5 times lower compared to the effectiveness during the 1980s. Consequently, the current concern about the Arctic charr population, and the fishery in Lake Geneva, is two-fold: first, the long process of reoligotrophication does not allow for the restoration of self-sustaining Arctic charr populations; second, the stocking effectiveness decreased strongly over the last 30 years. Even if stocking greatly contributes to catches, it still does not ensure a sustainable fishery at a high level. [Copyright &y& Elsevier]

Residential development on lake shores is regularly associated with the conversion of natural littoral habitats to riprap, sheet piles, beaches, parks, or marinas. The subsequent loss of littoral vegetation induces a decline of structural diversity and impacts littoral fish communities. These impacts may be shaped by lake morphology. Using boosted regression trees (BRT) to relate fish abundance data from 57 north-east German lowland lakes to various factors characterizing trophic state, lake morphology, and shoreline development, we investigated the response of 11 fish species to shoreline development. The analyses revealed that mean depth followed by trophic level and shoreline length (SL) contributed most in explaining littoral fish abundance. BRT models built for deep and shallow lakes separately confirmed that primarily trophic level and SL influenced fish abundance but that littoral vegetation was relatively more important in deep compared to shallow lakes, indicating that the effects of shoreline development may be more pronounced in deep lakes where the littoral makes up a smaller proportion of the lake area as compared to shallow lakes. The BRT further demonstrated species-specific responses to shoreline degradation, indicating that the reliability of ecological quality assessments of lakes can be improved by applying separate metrics for individual species. [ABSTRACT FROM AUTHOR]

daily changes in the vertical distribution of phytoplankton biomass were investigated. In both lakes, phytoplankton biomass in metalimnion were two or three times higher than in epilimnion. In Rogóźno Lake, Planktothrix rubescens dominated in phytoplankton (> 80% of biomass), whereas in Zagłębocze Lake − Ceratium hirundinella prevailed (> 90% of biomass). The biomass maxima of Pl. rubescens (at 6 m depth - 43.5 mg dm-3 and at 7 m depth - 24.4 mg dm-3) were always below the lower limit of the euphotic zone, i.e. at the depth where the light was < 1%, and the water temperature was < 10 °C. Large biomass of C. hirundinella was observed always in metalimnion (up to 43.6 mg dm-3 in July) at the lower limit of the euphotic zone (transparency of Sd = 3.0 m). In August, when transparency of Sd = 2.5 m, biomass of C. hirundinella varied significantly during the day in the two thermal layers. In epilimnion, the largest increase of biomass was observed in daylight hours and the decrease at night. The reverse situation was observed in metalimnion − the decline in the daytime and the increase at night. The studies revealed that despite different mechanisms of motility (buoyancy or flagellar movement), vertical migrations of these species corresponded mainly to the changing light. [ABSTRACT FROM AUTHOR]

Two halophilic archaeal strains, R30 and tADL, were isolated from an aquaculture farm in Dailing, China, and from Deep Lake, Antarctica, respectively. Both have rod-shaped cells that lyse in distilled water, stain Gram-negative and form red-pigmented colonies. They are neutrophilic, require >120 g/l NaCl and 48-67 g/l MgCl for growth but differ in their optimum growth temperatures (30 °C, tADL vs. 40 °C, R30). The major polar lipids were typical for members of the Archaea but also included a major glycolipid chromatographically identical to sulfated mannosyl glucosyl diether (S-DGD-1). The 16S rRNA gene sequences of the two strains are 97.4 % identical, show most similarity to genes of the family Halobacteriaceae, and cluster together as a distinct clade in phylogenetic tree reconstructions. The rpoB′ gene similarity between strains R30 and tADL is 92.9 % and less to other halobacteria. Their DNA G + C contents are 62.4-62.9 mol % but DNA-DNA hybridization gives a relatedness of only 44 %. Based on phenotypic, chemotaxonomic and phylogenetic properties, we describe two new species of a novel genus, represented by strain R30 (= CGMCC 1.10593 = JCM 17270) and strain tADL (= JCM 15066 = DSMZ 22187) for which we propose the names Halohasta litorea gen. nov., sp. nov. and Halohasta litchfieldiae sp. nov., respectively. [ABSTRACT FROM AUTHOR]

Restoration of anthropogenically eutrophied lake ecosystems is difficult due to feedback mechanisms that stabilize the trophically degraded state. Here, we show rapid recovery of a eutrophic stratified lake in response to multiple restoration that targeted the feedback mechanisms of high external and internal nutrient loads, lack of a trophic cascade, and lack of structured littoral habitats. Lake Tiefwarensee (Germany) was exposed to aluminium and calcium treatment and fisheries management over 5 years. Within this period, in-lake phosphorus concentrations declined by more than 80%, and transparency, zooplankton biomass and fish assemblage structure and biomass responded immediately and almost linearly to the reduction in phosphorus concentrations. Phytoplankton biomass and chlorophyll a (chl a) concentrations likewise decreased in response to restoration, but the declining trend was interrupted by one recovery year with unusually high phytoplankton biomasses. The zooplankton:phytoplankton biomass ratio and the chl a:phosphorus ratio approached values observed in other stratified lakes during natural recovery from eutrophication. The slow response of Tiefwarensee to the reduction of external load, and the quick response to the chemical treatment suggest that the disruption of internal P recycling and loading was the decisive restoration measure in Tiefwarensee. The external load reduction was a necessary but not sufficient measure, at least in the short-term, whereas the low-effort fisheries management was of minor importance. A comparison with other case studies confirms that measures aiming to inactivate phosphorus are the most efficient approaches to restore stratified lakes in the short-term, but a shift to a permanent near-pristine state is possible only by additional P input control. [ABSTRACT FROM AUTHOR]

The deep-lake facies of the Yanchang Formation represents a large outflowing lake basin in the Ordos area. Its deposition can be divided into four stages: lake genetic and expanding stage, peak stage, inversion stage and dying stage. All the stages are obviously consistent with the evolution of depositional environment and the paleoclimate in the region. The study indicates that the lake basin has evolution fluctuations from highstand to lowstand for four times in its evolution history, and the deposition center of the lake has not obviously moved, staying along the Huachi-Yijun belt. The deep lake sedimentary system mainly consists of deep water deltas and turbidite fans during the entire evolution course of the lake basin in the Late Triassic. The former mainly developed on the slope of steep shore of the delta in the early period of the deep-water expansion and gradually experienced a big shift from deep-water deltas to shallow-water platform delta. And the latter appeared almost in all the above stages and had two types of turbidite fans, slope-moving turbidite fans and slump turbidite fans. The slope-moving turbidite fans have relatively complete facies belts overlapping one another vertically and consist of the slope channel of inter fans, the turbidite channel, inter turbidite channel and turbidite channel front of middle fans and outer fans (or lakebottom plain). However, the slide-moving turbidity fans are formed in the deep lake with their microfacies difficult to be distinguished, and only the center microfacies and edge microfacies can be determined. The two types of the turbidity fans are similarly distributing in the near-root-slope and far-root-slope regions. The deep-lake deposition governs the distribution of the hydrocarbon and reservoir, while the slope-moving turbidite fans are excellent reservoirs for oil-gas exploration due to their great thickness, widespread distribution and accumulation properties. [ABSTRACT FROM AUTHOR]