Assessment of the current ecological state of the Russian section of the transboundary Irtysh river based on the structural parameters of phytoplankton

Based on the materials of studies in 2019 of phytoplankton in the Russian section of the transboundary Irtysh River (middle and lower reaches), the species composition, taxonomic structure, and distribution of phytoplankton abundance along the river were established. The basis of the species richness of phytoplankton is created by green algae (Chlorophyta group), Cyanoprokaryota, Bacillariophyta and Euglenophyta play a significant role. The maximum abundance of phytoplankton was observed in the summer-autumn period. Throughout the entire length of the river, small-celled, heterocyst-free cyanoprokaryotes, chlorococcal and centric diatoms intensively vegetate in phytoplankton in the summer-autumn period. The influence of settlements on the indicators of phytoplankton abundance along the river is most noticeable in the Omsk region. Below the city in the river the number of phytoplankton significantly increases due to the intensive vegetation of heterocyst-free cyanoprokaryotes. At that, the growth of biomass is mainly due to the development of centric diatoms, among which the share of anthropogenic eutrophication of Stephanodiscus hantzschii Grun is noticeable. The water quality in the river corresponded to the 3rd class of satisfactory purity, the trophic status ranged from mesotrophic to eutrophic category. The parameters of alpha diversity indicate a prosperous state of the phytoplanktocenosis of the Irtysh. Anthropogenic ecological stress of the Irtysh ecosystem persists to the present time, but in general, the river ecosystem is in a fairly stable state of ecological modulation.