Temporal and Spatial Dynamics of Plant Pigments in Bottom Sediments of the Volga River Reservoirs

New data on the contents of plant pigments in bottom sediments of the Volga River reservoirs in the summer of 2015–2021 are presented. It has been shown that the production properties of benthal do not differ significantly from those at the end of the twentieth century. The concentrations of chlorophyll a and its degradation products, pheopigments, in the upper 5-cm layer of sediments decrease from the Upper Volga to the Lower Volga and its unregulated part, with the exception of the Cheboksary Reservoir with high values of pigment indicators. The spatial dynamics of sedimentary pigments largely depends on the morphometry of reservoirs and hydrodynamic activity affecting the distribution of bottom sediments. The concentrations of sedimentary pigments are positively related to the content of organic matter, water content, and the total contribution of aleuritic and pelitic fractions, and negatively related to the water current velocity, the mean diameter of particles, and volumetric mass of bottom sediments. It has been shown that the relationship between pigment content and depth in the reservoirs of the lower part of the cascade is weakened. During the study period, no temporal trends in the content of sedimentary pigments in reservoirs were identified. The average concentrations of sedimentary pigments in 2015–2021 characterize benthal in the Ivankovo reservoir as hypertrophic, in the Uglich, Rybinsk, Gorky, and Cheboksary reservoirs as eutrophic, in the Kuibyshev, Saratov, and Volgograd reservoir as mesotrophic, and in the unregulated Volga as oligotrophic. The content of chlorophyll a (with pheopigments) in bottom sediments in terms of the conditional biomass of algae amounts an insignificant part (0.24–0.86%) of the primary production of phytoplankton, the main producer of organic matter in the Volga River reservoirs.