Phytoplankton and Phytoperiphyton Characteristics of Lake Pyasino and Its Tributaries after an Accidental Fuel Spill in 2020

— An assessment of the species composition, abundance, biomass, and pigment characteristics of phytoperiphyton and phytoplankton of Lake Pyasino, its tributaries (Bezymyannyi Stream, Daldykan, Ambarnaya, and Norilskaya rivers), and the head of the Pyasina River has been carried out after a manmade accident (a diesel-fuel spill near the city of Norilsk in May 2020). A significant decline in the biomass and changes in the species composition of phytoperiphyton after the water was contaminated by fuel is revealed only near the spillage site (in the Daldykan River and the Ambarnaya River downstream the mouth of the Daldykan). Downstream, in the Ambarnaya mouth zone, as a response to the release of a large amount of nutrients during the decomposition of fuel products and dead organisms, as well as the mechanical cleaning of the bank line, there has been a massive growth of diatom and green algae ( Tabularia tabulata , Spirogyra sp.) in the water column and the appearance of indicators of organic pollution (Euglenophyceae and Cryptophyceae). No significant changes in the plankton of Lake Pyasino and the Pyasina River in comparison with the data obtained in the second half of the 20th century (i.e., long before the accident) are found. Species composition and quantitative features, as well as amount and ratio of pigments, characterized the phytoplankton and phytoperiphyton of Lake Pyasino and the Pyasina River as a normally functioning freshwater community of oligotrophic waters. All this indicates the absence of a negative impact of the accidental fuel spill on the ecosystem of Lake Pyasino and the Pyasina River.