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Salinity largely determines the species diversity and structure of the food web in lake ecosystems. Many studies have been focused on the salinity tolerance of various plankton species. There are fewer studies investigating the modifications in the food web interactions under the effect of salinity. An appropriate system for such studies is closely located lakes of different salinity. We took samples during the summer stratification and analyzed the physicochemical and biological characteristics of 20 lakes (salinity 0.1-35 g/l) in southern Siberia in order to provide general description of this system and to test a number of hypotheses about the effect of salinity on the structure of the food web. The analysis revealed two key factors structuring ecosystems of the studied lakes. The species composition of zooplankton was determined by salinity, with a decrease in the number of species and the transformation of the community from a diverse community of zooplankton (salinity up to 3 g/l) to the dominance of large daphnia (3-8 g/l), copepods (> 8 g/l), small cladocerans and rotifers (20-30 g/l), and Artemia (> 30 g/l). The top predator (fish) was eliminated at salinity above 10 g/l. The biomass of zooplankton did not depend on salinity, but significantly increased in lakes with an increased nutrient load. The nutrient load also had a significant effect on the concentration of total phosphorus, turbidity and transparency of water, and the concentration of chlorophyll “a”. Thus, we recorded the structuring effect of the nutrient load (bottom-up control) on the biomass of the trophic levels and the parameters of water transparency, while salinity transformed the trophic chain from the top, leading to the disappearance of fish and a change in the dominant species of zooplankton. At the same time, salinity did not affect the biomass of the trophic levels. In order to detect top-down effects in the ecosystems of saline lakes, it is necessary to perform a comparative analysis of the seasonal dynamics of ecosystems of lakes with different salinity

In recent decades, freshwater ecosystems have regularly experienced blooms of green algae (green tides), causing environmental and economic damage. Blooms of green alga Spirogyra sp. occur in the ‘Abakanskaya’ anabranch of the Yenisei River in summer months. The anabranch is influenced by several anthropogenic factors: construction of a dam in the upper reaches; heated water discharge from a thermal power plant; fish farming. The aim of this study was to assess the impact of anthropogenic factors on the ecosystem of the Abakanskaya anabranch and to identify the main factors favoring Spirogyra sp. blooms. Samples were taken in May-September 2018-2019 at four sites: 1 – upstream of the dam (control), 2 – downstream of the dam, 3 – near the point of heated water discharge, 4 – downstream of the fish farm. Physical and chemical parameters, biomass and species composition of phytoplankton, phytoperiphyton, zooplankton, zoobenthos, and higher water plants, gross primary production (GPP), nitrogen content in biomass of periphyton, higher plants, and zoobenthos were studied. The main factor that caused changes in the community was that there was no water flow in the anabranch because of the low capacity of the dam drainage pipes. While upstream of the dam most ecosystem features were within the limits typical for this part of the Yenisei River, downstream of the dam, the system seemed to change from lotic to lentic: percentage of motile forms of phytoplankton, biomass of zooplankton, percentage of true zooplankton species, taxon number and taxonomic diversity of zooplankton and zoobenthos became higher; phytoperiphyton primary production rose (because of Spirogyra sp. bloom); higher water plants thrived. The other investigated factors, namely, thermal, nutrient, and organic pollution evidently produced combined effect on the ecosystem because of the absence of water flow, and their specific effects were not obvious

Traditionally, the abundance, cell size distribution and species identification of algae are determined by microscopic counts. In recent years, various rapid methods have been developed for routine algal studies. However, each of these methods has its drawbacks. It is important for aquatic ecologists to understand the advantages, disadvantages, and limitations of these methods. We compared the sensitivity of three rapid methods (multichannel fluorimeter FluoroProbe, imaging flow cytometer FlowCam, and CASY particle counter) to changes in cell abundance of three algae species (Chlorella vulgaris Beyerinck, Arthrospira platensis Gomont, and Nostoc sp.). We also assessed the ability of rapid methods to estimate the cell abundance of different species in the mixed samples. All instruments showed high sensitivity to changes in the cell abundance of different algae species and a mixture of these species. Any one of these methods, once calibrated, can be reliably used to estimate the abundance of a single-species/laboratory culture of microalgae. At the same time, FlowCam, without preliminary calibration, recorded the cell abundance closest to microscopic counts. When analysing a mixture of three microalgae differing in their cell sizes and spectral characteristics, FluoroProbe showed the highest accuracy in assessing the proportions of species in the mixture and FlowCam – in assessing their abundance. To study mixtures of algae and/or natural phytoplankton communities, it is advisable to use jointly a flow cytometer and a multichannel fluorimeter. The images of algae saved by the flow cytometer, if necessary, can be used to identify them, with a certain accuracy, to the species. Information on cells size and spectral characteristics obtained by two methods will be detailed enough to perform such common tasks as studying trophic interactions between phyto- and zooplankton or creating warning systems to inform of unwanted blooms of phytoplankton and their individual groups (for example, cyanobacteria)

Midges (Chironomidae, Diptera) are dominant amphibiotic insects in zoobenthos of the large saline Lake Shira located in the arid landscape of South Siberia. During two vegetation seasons we measured the dynamics of chironomid emergence from littoral parts of four stations in the lake. During one of the vegetation seasons we also measured chironomid emergence from profundal parts (depth of 6 m) of the same stations using original floating traps. Both seasonal dynamics and daily means of emergence values significantly varied among the studied stations and depths and were related to the bottom sediment type. The annual export of wet biomass (calculated as the sum of daily values for a vegetation season) was equal to 0.61 g per square meter of water surface and included proportional contributions of the areas with various bottom sediment types. Based on the values of benthic secondary production, we estimated additional annual export of chironomid biomass from the profundal part of the lake of approximately 1 g of wet weight · m−2. Besides, the total export of polyunsaturated fatty acids (PUFA) calculated using the previous data on PUFA content in the studied chironomid taxa (~ 2 mg · m−2 year−1) appeared to be one of the lowest when compared to estimations for chironomids and some other amphibiotic taxa from similar steppe landscapes