PHYTOPLANKTON - COMMUNITY STRUCTURE, SUCCESSION AND CHLOROPHYLL CONTENT IN LAKE MUGGELSEE FROM 1979 TO 1990

One aspect of the present work on Lake Muggelsee has been a quantitative assessment of phytoplankton changes over the annual cycle and from year to year as a basis for primary production measurements. The investigations of plankton analysis were carried out in Lake Muggelsee (Grosser Muggelsee, Berlin), a eutrophic, polymictic shallow lake with an area of 7.2 km2, a mean depth of 4.9 M. The lake was described as a species rich water with partially considerable developments of diatoms and blue-green algae as was shown by plankton analyses from the beginning of this century. Since the end of the 60s, when macrophytes disappeared, Lake Muggelsee has been recognized as a lake with extensive phytoplankton development characterized by dense and irregular development of blue green algae and diatoms. Especially solitary centric diatoms increased in number and in biovolume from 1979 to 1990 and occurred with greater diameters in spring during the seasonal course. The specific content of chlorophyll a was estimated according to the algal composition. It is suggested that the observed decrease in Chl a per unit biovolume is associated with species size rather than the time of development depending on the unknown portion of inactive algal cells resuspended from the sediment surface.