Analysis of the Phytoplankton State in Low Mountain Lake Manzherok (Gorny Altai) Using Hydrooptical and Hydrophysical Characteristics

The composition, development, and distribution of the phytoplankton, as well as the hydrooptical and hydrophysical characteristics, were studied in the eutrophic–polytrophic, low-flow, low-mountain, ancient Lake Manzherok (Altai Republic) in April and July 2021. Twenty-nine algae taxa with a rank below the genus level vegetated in the ice-cover period, with an ice thickness of 0.45–0.50 m and a thin snow layer with thaws at a water temperature of 0.1–4.6°C. Their biomass reached 15.9 g/m3 (mean value 11.5 g/m3), Chl a content 2.79 mg/m3, Chl b 58.11 mg/m3, and Chl c 35.81 mg/m3. Summer phytoplankton at a temperature of 24.2–25.5°C was characterized by higher diversity (72 taxa) and higher biomass (up to 7813.3 g/m3, a mean value of 1960.4 g/m3), and higher Chl a content 16.82 mg/m3 and by a lower content of Chl b (10.87 mg/m3) and Chl c (30.54 mg/m3). The strongest relationship between optical properties in situ and the abundance of algae was found between the light absorption coefficients with wavelengths of 520, 550, 580, and 610 nm and cyanobacteria biomass and between the light absorption coefficient with wavelength of 460 nm and the total biomass of green and euglenic algae.