No abstract

Unstable water level regime in the Kuibyshev Reservoir affects coastline formation as well as allocation and development of aquatic vegetation on the coast. These factors determine the composition and structure of biocenosis in shallow waters of the reservoir. The aim of this study was to reveal the patterns of formation, distribution and dynamics in phytoplankton communities in the shallow coastal waters on two reaches of the Kuibyshev Reservoir (Volga and Volga-Kama, Russia). These reaches differ by the extent of anthropogenic influence, protection from wind and waves and other environmental conditions. The research was done during the growing season of 2002 in the thickets of Typha angustifolia L. and Phragmites australis (Cav.) Trin. Ex Steud., as well as in the open water areas. Seasonal changes in the total biomass and abundance of phytoplankton in the thickets of macrophytes and in the open areas of the reservoir differed little. On the outer edge of the thickets, where intensive contact with the open water occurs, the highest algal species diversity and abundance were revealed, which is known as the ''edge effect''. Two peaks of phytoplankton development with maximums in June-July and late August were observed. By the end of the summer, a decrease in water level led to the autumn outbreak in volvocine algae abundance and biomass. The maintaining of an optimal water level in the reservoir is recommended for controlling of water ''blooming'' and thus maintaining high water quality.

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The paper presents the results of a comparative analysis of planktonic algae structure in the Volga and Kama rivers at the confluence of the Kuibyshev reservoir. The author has also assessed the trophic state of the studied river sections in 2012. The hydrochemical regime of the Kuibyshev reservoir is heterogeneous and is determined by the chemical composition of the Volga and Kama waters, which differ in the ratio of ions and mineralization. The ionic composition of the Kama waters is often dominated by sulfates. The salinity depending on the season and water content of the year ranges from 168 to 674 mg/l. The Volga waters contain calcium bicarbonate and have a lower mineralization (120130 mg/l). The variability of the incoming water, the amount of runoff, the degree of volume drawdown within water bodies and groundwater inflows primarily affect the conditions for planktonic algae existence. In the phytoplankton of the Volga and Kama rivers (areas before their confluence in the Kuibyshev Reservoir), 123 taxa of algae were identified during the 2012 growing season. The waters of the Volga River have a higher species diversity (107 species). The phytoplankton of the Kama River is less diverse (76 species). In the seasonal dynamics of phytoplankton in the studied river sections, two peaks of abundance and biomass are observed by the middle of summer and at the end of it, when the maximum values of abundance and biomass are reached. The waters of the investigated sections of the Volga River is characterized by a complex of phytoplankton of blue-green, diatoms and green algae, while the Kama River is dominated by diatom phytoplankton. In summer and autumn the blooming of water in both rivers is due to the massive development of blue-green algae of the genera Microcystis, Aphanizomenon, Anabaena, Oscillatoria. The waters of the Volga and Kama rivers in 2012 during the study period corresponded to the mesasaprobic type and moderately polluted zone; the waters of the Kama River had higher saprobity indices. The trophic status of the rivers under consideration in the study area was mostly related to the eutrophic type; during the periods of maximum reproduction of blue-green algae to the hypereutrophic type.