Plankton community of the lower course of the Kama River in the late autumn period

Abstract

Abstract The features of the plankton community structure and transformation have been investigated in the lower course of the Kama River in the late autumn 2020. The transformation of organic matter and seston composition of the Kama River was affected by the inflow of the largest tributary (the Vyatka River) and by the operating mode of the Nizhnekamsk hydroelectric power station. Three structural groups of plankton have been defined: the Kama River community (upstream the confluence with the Vyatka River), the Vyatka River community, and the transformed community downstream of the Vyatka River confluence. The waters of the Vyatka River were characterized by the highest plankton biomass, which affected the quantitative indicators of the Kama River community downstream the tributary inflow. The transformation of the planktonic community under the influence of the Vyatka River inflow was manifested in the change of one dominant group (heterotrophic bacteria) to another (diatoms). In general, despite the lower volume of Vyatka runoff compared to the Kama River, 81% of the total organic carbon of plankton on weekends, and 61% on working days, was formed due to runoff from Vyatka. On the contrary, detritus mainly came directly from the Kama River waters (more than 97%). The influence of the Vyatka River on the Kama River ecosystem in its lower course and further on the Volga River was large, increasing even more on weekends as the amount of runoff through the hydroelectric power station reduced.