Zoning factors and their influence on the lakes’ zooplankton in the Middle Volga Region (Russia)

We analyzed the results of studies of 176 different types of lakes in the Middle Volga region (Russia). The impact of various environmental factors (morphometric parameters of lakes, physical and chemical indicators of water) on the lakes’ zooplankton communities of two landscape-geographical zones (forest and forest-steppe) was studied. The aim of the work was to identify the biodiversity of pelagic zooplankton and to assess the role of environmental factors in the development of zooplankton communities. Statistical studies included the calculation of the Spearman and Pearson correlation coefficients, data analysis using linear and logistic regression methods. We identify 230 species of zooplankton, including Rotifera – 107 (45.6%), Cladocera – 76 (33.6%), Copepoda – 47 (20.8%). Forest lakes show more species in the sample and higher quantitative indices compared to the forest-steppe lakes. The values of these indicators are determined by a complex of factors, the most important of which are the morphometric parameters of the lakes, the content of mineral nitrogen, oxygen, water mineralization and its determining ions. The depth of the reservoir can increase in the number of species in the sample or decrease them. Zooplankton quantification decreases as maximum depth increases. In deep-water lakes they are usually lower than in wellwarmed high-trophic and shallow ones. High mineralization and higher content of nutrients reduce the number of species in the sample and quantitative indicators of zooplankton. The increase in mineral nitrogen concentration and average ranking index is negatively related to zooplankton abundance, which is due to the occurrence of negative effects associated with anthropogenic eutrophication. Local conditions determine the composition and structure of zooplankton communities within the landscape-climatic zones, which determine the ionic composition of water and the concentration of major ions.