Re-assessment of Wundsch's (1940) ‘H2S-Oscillatoria-Lake’ type using the eutrophic Lake Scharmützel (Brandenburg, NE Germany) as an example

Abstract

Thienemann's 1922 ‘biological lake’ classification indicates the increase in the trophic level of lakes. It is based on the sucession of the disappearance of certain benthic indicator organisms in relation to the gradient of a decreasing O2concentration in the deep water, i.e. from O2-sensitive Chironomidae spp. (non-biting midges) to the less sensitive Chaoboridae (phantom midges) larvae. As early as the mid 1930s, several lakes in Brandenburg, e.g. Lake Scharmutzel, belonged to the last category of this classification. They were O2-deficient in deep water during summer and lacked the Chironomidae larvae. Simultaneously, filamentous cyanobacteria (Oscillatoriales) appeared. This lead to the replacement of Thienemann's indicators, i.e. O2 by H2S and Chironomidae by Oscillatoriales, and to Wundsch's 1940 new ‘H2S-Oscillatoria-Lake’ type. Since H2S and Oscillatoriales were not clearly identified as symptoms of eutrophication, it is not justified to use them to characterise a separate lake type. However, these indicators are of ecological importance, since the regional and common creeping increase in SO42- concentration favoures the current high H2S formation. The successive deterioration in O2 conditions, the increase in the extent of H2S formation related to the decrease in species diversity clearly indicates that Lake Scharmutzel reached a qualitatively new state of eutrophication within 60 years.