The species composition and biomass of phytoplankton in the eutrophic Lake Lovojärvi, southern Finland

Phytoplankton species composition and biomass in relation to the concentration of pigments were studied in Lovojärvi, a small, but deep, brown water lake, from 25. IV. 1974 to 6. I. 1975. The vigorous blooms of Cyanophyta observed in 1971 did not recur, because the summer was cooler than usual. The mean phytoplankton biomass during the ice-free period was 13.3 g/m² in the trophogenic layer. Biomass showed peaks occurring at intervals of one month. The greatest biomass was recorded at the end of May. Diatoms dominated in spring, and Peridinium bipes caused a peak in September. The proportion of chlorophyll a in fresh weight averaged 0.36 % during the ice-free period. The percentage was clearly dependent on the species composition and the season; it was smallest when diatoms dominated, but exceptionally high in the middle of the winter. The proportion of chlorophyll b was highest in summer at the lower boundary of the euphotic zone.