LAUSR

Phytoplankton composition, development, and distribution, as well as hydrooptical characteristics, were studied in mesotrophic drainless Lake Krasilovskoe (Altai krai, Russia) in March and August 2017, and February 2018. Phytoplankton comprised 147 taxa with a rank below genus. In winter, the phytoplankton abundance was 0.03–1.06 × 106 cells/L, biomass 0.2–12.2 g/m3, and Chl a content 1.8–24.1 mg/m3 at a snow depth of 0.13–0.34 m, ice thickness of 0.56–0.70 m, and water temperature of 0.1–4.5°C. Summer phytoplankton was characterized by higher values of indicators of development (0.11–1.74 × 106 cells/L, 0.6–18.2 g/m3, and 27.5–83.4 mg/m3 Chl a, respectively). A positive relationship between the Chl a content and the absorption coefficient in the range of 400–460 and 670–800 nm and the total phytoplankton abundance and absorption coefficient in the range of 520–580 nm was found both in winter and summer periods. This indicates that active photosynthesis in algae takes place not only in summer, but also during the ice period.