Plant Pigments in Water of the Volga River Reservoirs: Current Status, Trends in Long-Term Changes

Data on the composition and content of photosynthetic pigments in plankton of the Volga River reservoirs in summer period of 2015–2023 are under consideration. The determination of pigments was carried out using standard spectrophotometric methods. Chl a concentrations are close to those obtained in 1989–1991. The distribution of Chl a throughout the water area of reservoirs retains its long-term characteristics. The waters of tributaries, coastal waters, and shallow water areas are characterized by an increased abundance of phytoplankton. A negative relationship between reservoir-average Chl a concentrations and the total inflow volume (R² = 0.50) and a direct dependence on water temperature (R² = 0.35) were revealed. Based on the average Chl a concentrations over the years of observation, the current trophic status of the Ivankovo, Uglich, and Cheboksary reservoirs is assessed as eutrophic (29.5±1.9, 22.7±1.6 and 28.2±2.7 µg/L respectively), the Saratov and Volgograd reservoirs are mesotrophic (6.8±0.6 and 9.6±0.8 µg/L), Kuibyshev and Gorky reservoirs are moderately eutrophic (13.0±0.7 and 13.1±1.4 µg/L). The content of additional chlorophylls b and c, pheopigments, plant carotenoids and their ratio with chlorophyll a, as well as the composition of green pigments in the Volga River reservoirs are characterized by significant similarity and have not changed over the 30-year period.