Comparative analysis of the structure of planktonic algae of the Volga and Kama rivers before their confluence in the Kuibyshev reservoir (the Republic of Tatarstan, RF)

The article presents the results of comparative analysis of the structure of planktonic algae in the Volga and Kama rivers, as well as the assessment of the trophic state of these water bodies, which form the Kuibyshev reservoir at their confluence. The hydrochemical regime of the Kuibyshev reservoir is nonhomogeneous and is determined by the chemical properties of the Volga and Kama, differing in the ratio of ions and mineralization. The ionic compositionin Kama is often dominated by sulfates. Its mineralization ranges from 168 to 674 mg L^-1, depending on the season and dryness of the year. The Volga contains calcium hydrocarbonate and display a lower degree of mineralization (120-130 mg L^-1). Different composition of the incoming water, runoff rate, the degree of volume drawdown, intra-basin processes and groundwater inflows exhibit a direct impact on the conditions for the existence of planktonic algae. During the growing season of 2012, 123 algae taxa were identified among the phytoplankton of the Volga and Kama rivers (the areas before their confluence in the Kuibyshev reservoir). In terms of species diversity, diatoms and green algae were prevalent. The Volga exhibits higher species diversity (107 species), while the phytoplankton in Kama displays less diverse (77 species). In the seasonal dynamics of phytoplankton in both areas, two peaks of abundance and biomass are observed, i.e., at the middle and at the end of summer. The studied areas of Volga River are characterized by a phytoplankton complex of blue-green, diatoms and green algae, while diatom phytoplankton predominates in Kama River. In the summer-autumn period, the "blooming" of water in both rivers is connected with massive development of blue-green algae of the genera Aphanizomenon, Microcystis, Anabaena and Oscillatoria. During most of the growing season, the waters of Volga and Kama rivers belong to the mesasaprobic type and correspond to the moderately-polluted zone. Moreover, the waters of Kama River are characterized by higher saprobity indices. The trophic status of studied rivers mostly corresponds to eutrophic type, and in the periods of maximum development of planktonic algae - to hypereutrophic type.