Composition, Structure, and Distribution of the Phytoplankton of a Highly Mineralized Karst Lake

The features of the composition, development, and spatial distribution of the phytoplankton of highly mineralized karst Lake Klyuchik (Nizhny Novgorod oblast) are considered. The lake has a pronounced ecotone with respect to the hydrological and hydrochemical parameters. A unique algocenosis with a high quantitative development (the biomass is over 130 g/m3, which is unusual for middle-water bodies) and the dominance of centric diatom Cyclotella distinguenda Hustedt. (a rare species that is untypical for the water bodies of the Middle Volga) have been revealed in the western part of the lake and in the ecotone zone. The vertical phytoplankton distribution shows the bottom maximum in the ecotone zone and in the maximum depth area.