COMPARATIVE ANALYSIS OF ECOLOGICAL STATE OF WINTER AND SUMMER PHYTOPLANKTON IN DRAINLESS MESOTROPHIC LAKE (ALTAI KRAI, RUSSIA)

The investigation findings are of interest in the fundamental hydrobiological studies and new methodological approaches to the phytoplankton ecological state assessment. In mesotrophic-eutrophic lake the active vegetation of plankton algae was revealed at the end of winter under snow (0.13-0.34 m) and ice (0.56-0.70 m) layers at water temperature of 0-4.5 °C along the water column (6 m depth). The winter phytoplankton involved species from Chlorophyta, Bacillariophyta, Euglenophyta, Dinophyta, Cryptophyta, Ochrophyta and Cyanobacteria. The maximum abundance and biomass are due to passive plankters, incapable of active phototaxis from Microcystis, Gomphosphaeria, Chroococcus, Anabaena, Gloeocapsa, Cyanothece, Monoraphidium, Scenedesmus, Dictyosphaerium and Hyaloraphidium genus. In the ice cover period, the species number reaches 52-56, the abundance – 26.4-1056.0 th. cells/l, biomass – 0.2-12.2 g/m 3 , the chlorophyll a concentration – 1.8-24.1 mg/m 3 . Although these characteristic values appeared to be high for the cold period (at low temperature and insufficient light), they were lower than in the summer season (more than 100 species, 0.11-1.74 mln. cells/l, 0.64-18.16 g/m 3 and 27.49-83.40 µg/m 3 , respectively). It is noted that algae growth in winter period was limited by the depth of snow cover, but not of the ice. Water temperature affects the species composition and chlorophyll a concentration, but not the algae abundance and biomass. The microscopic method results for determining the plankton algae concentration were compared with the non-contact methods of investigation (spectrophotometric method of light attenuation recording). The assumption that since algae photosynthesis is most active in the blue (wavelength is 400-460 nm) and red (670-800 nm) spectral zones, the absorption of these light waves will be maximum, was confirmed by experimental data. The trend of increasing algae abundance, chlorophyll a concentration and spectral light attenuation in the blue and red light from the surface to the bottom during the summer season and the ice cover period at 0.13 m snow depth was noted.