Biomass of phytoplankton and content of chlorophyll "A" in the rivers of the Kuybyshevskoe, Saratovskoe and Volgogradskoe reservoirs

Data on the biomass and chlorophyll-a content in the phytoplankton of some river tributaries of the Kuibyshev, Saratov and Volgograd reservoirs are given. The taxonomic and structural characteristics of phytoplankton are dependent on hydrological factors; their connection with the content of nutrients in conditions of eutrophy was not revealed. The limits of the change in the phytoplankton biomass in the rivers were 0.01 to 6.40 mg/l, the chlorophyll-a concentration 0.01 to 13.71 μkg/l, the specific chlorophyll-a content in biomass 0.36-1, 48.The level of biomass and the content of chlorophyll-a in the Usa river and its tributaries, as well as in the investigated sections of the Chagra river generally correspond to oligo- mesotrophy. Trophic status of the B.Irgiz river, estimated by phytoplankton indicators, varies from oligo- mesotrophy to eutrophy in some areas. Despite the dynamics of quantitative indicators, there is an increase in the biomass and concentration of chlorophyll «a» downstream. For the estuaries of rivers, the presence of a hydrological backwater and the features of its influence on the regime of the lower course of the river are of great importance. The investigated watercourses are characterized by a positive correlation between the biomass of algae and the concentration of chlorophyll-a. An analysis of the variation in the composition of the dominant algal groups and the specific chlorophyll-a content in the plankton of the rivers revealed a statistically significant dependence of these indices only on the biomass of Chlorophyta algae.