Long-term changes in the composition and biomass of the phytoplankton in Lake Niegocin (Great Mazurian Lakes, Poland)

Abstract

Long-term and seasonal studies were made on the changes of phytoplankton composition and biomass in a strongly polluted, eutrophic, dimictic Lake Niegocin. Two maxima were distinguished in the seasonal development of the phytoplankton: spring and summer one. During the studies, in 1978 and in 1986 - 1989 diatoms dominated in the phytoplankton during spring circulation. Their biomass ranged from 1.9 to 18.1 mg^.dm^-3. Summer maximum of phytoplankton development was caused by mass development of blue-green algae, up to 97.8% of the total phytoplankton biomass. Range of average phytoplankton biomass in the peak of development was narrow in particular years, from 5.8 to 8.9 mg^.dm^-3. The paper presents also an analysis of the relationships between phytoplankton development and selected environmental factors.