LAKE MUGGELSEE AND THE INFLOWING RIVER SPREE - COMPARISON OF PHYTOPLANKTON COMMUNITIES 1980-1990

Biomass and community structure of phytoplankton have been analysed in the eutrophic, shallow, polymictic Muggelsee and in the inflowing Spree since 1980. In both lake and river, mean biomass and vitality of phytoplankton were similar. A regular annual succession of planktonic algae was found in both the river and the lake. The same species were found to be dominant, although the actual biomass of single phytoplankton populations differed normally from inflow to lake. Lake phytoplankton was characterized by higher proportions of Cyanobacteria (45.9 +/- 11.3 % resp. 34.5 +/- 8.2 %) and lower proportions of centric diatoms (35.1 +/- 9.5 % resp. 41.9 +/- 10.3 %, average April-October, 1980-90). The less abundant Pennales, Chlorophytes, and unidentified planktonic algae < 10 mum had attained a relatively higher importance in the river than in the lake. In the last decade, a pronounced shift from Cyanobacteria to diatoms (mainly Centrales) has been observed in the river.