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The research assesses the state of different types of lakes in specially protected natural areas of the Nizhny Novgorod Region and the anthropogenically disturbed territory of Nizhny Novgorod. The trophic status of water bodies was determined using the trophic status index ( TSISD ). It has been established that most of the lakes have eutrophic and mesotrophic status. The analysis of the species structure of zooplankton in water bodies has been carried out. The species richness of both lakes of the protected areas and urban lakes was high. Along with eurybiontic species, alien and rare species of zooplankton were identified. Significant differences in the indicators of the species structure were established, however, no critical values of the abundance, biomass, Shannon and Pielou indices were recorded. Most of the identified zooplankton species were indicative. On the basis of the Pantle-Bukk saprobity index in the Sladecek modification, the water quality class was established. The reservoirs were characterized by quality class II-III (clean-moderately polluted water). In some lakes an excess of the maximum permissible concentrations of ammonium, nitrite, iron, manganese, copper, zinc, lead has been established. However, in general, in terms of a set of indicators, water bodies are in a satisfactory condition. In order to objectively assess the ecological state of aquatic communities, to predict possible changes and develop recommendations for the conservation of species diversity, it is important to carry out regular monitoring studies.

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Information on the functional traits of the most widespread species of freshwater zooplankton (Rotifera, Cladocera, and Copepoda) in European Russia was collected and analyzed. Our database includes 355 species described by 4 traits, namely: maximum body length, trophic group, feeding type, and movement type. Cluster analysis based on Gower's functional distances shows that freshwater zooplankton can be classified into 19 groups with different ecological roles. The characteristics of each identified functional group are presented. We believe it to be fundamentally important to build a unified classification using all available data and applicable characters for all three main taxonomic groups of zooplankton. Comparison with the existing ecological zooplankton classification proposed by Yu. S. Chuikov has demonstrated a number of advantages of our approach. Several ecological groups in Yu. S. Chuikov’s classification are represented by more fractional categories in our classification. Our system of functional groups can be used in studies of the structure of zooplanktocoenoses based on direct cluster analysis and ordination or based on functional distances between samples. To calculate the functional similarity between species, one can use our database of features, which is contained in the Appendix. Analysis based on functional groups gives a better unerstanding of the structure of a community than traditional ordination, which takes into account only the taxonomic affiliation of species. The approach used for functional group identification can be useful in assessing functional diversity and identifying patterns of freshwater zooplanktocoenoses dynamics. The database of functional signs of zooplankton can be used to check the relationship of functional signs with environmental factors.

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The gradients of hydrological, hydrophysical, and hydrochemical conditions form the transition zones in river mouth areas. These areas are considered ecotones in the presence of the edge effect. Our research aimed to identify the main patterns in the structural organization of zooplankton communities in different types of river mouth areas in lowland reservoir tributaries within the Middle Volga basin. A cluster analysis was performed to structure and determine the zooplankton communities. The identified zooplankton communities were characterized by the noticeable heterogeneity in the species structure. We analyzed the spatial distribution of the structural indicators of zooplankton communities and, on the basis of RDA, determined the factors that significantly affect the organization of the ecotone community. An ecotone was found in all types of river mouth areas where the highest density, biomass, diversity, species, and functional richness of zooplankton were noted, as compared to bordering zooplankton communities. As the morphological structure of the mouth areas became more complex, the values of the main structural parameters of zooplankton communities increased. It was demonstrated that conditions in the ecotones are favorable to the development of zooplankton alien species. The major factors determining the species structure of the ecotone zooplankton community were water electrical conductivity (R2 = 21.07%, p-value = 0.001), dissolved oxygen content (R2 = 10.33%, p-value = 0.003), and water transparency (R2 = 9.77 %, p-value = 0.001).