Mikrobielle Aktivität in dem huminstoffreichen Moorsee Große Fuchskuhle

Dystrophic lakes are characterized by a large pool of dissolved organic carbon (DOC) with a high portion of humic substances. These high molecular weight substances can be utilized by microorganisms releasing extracellular enzymes such as peroxidases, resulting in the formation of unstable radicals. Most organisms known for the production of extracellular peroxidases were found in terrestrial environments whereas investigations on these enzymes in the aquatic environment are rather rare. For investigations on microbial activities in a humic rich environment Lake Große Fuchskuhle has been chosen. This lake was artificially subdivided into four compartments which subsequently developed divergent chemical and microbiological characteristics. Thus, the DOC pool differed remarkably between the compartments. Due to a strong impact of the catchment area at one side of the lake two compartments are rich in humic substances whereas the other two compartments have a lower concentration of humic substances but a higher concentration of polysaccharides. Only few studies focus on the hydrogeology of lakes and the catchment area with respect to the genesis. In this thesis results are presented from field investigations on the water balance and on chemical fluxes between Lake Große Fuchskuhle and the catchment area. During high groundwater inflow into one compartment higher concentrations of DOC, nitrogen and phosphorus were detected. These findings then raised the questions i) whether specific bacterial groups rapidly respond to changes in DOC availability and ii) after their potential to degrade humic substances by extracellular enzymes. Seasonal changes of microbial community composition were studied in a humic rich and a humic poor compartment. These changes were compared to community shifts induced during short-term enrichment experiments. In these experiments beta-proteobacteria were enriched whereas Actinobacteria declined during the incubations. However, in Lake Große Fuchskuhle the beta-proteobacteria and Actinobacteria appeared in high numbers. In the humic rich compartment the abundance of beta-proteobacteria (beta II cluster) was significantly higher than in the humic poor compartment. The abundance of Actinobacteria was similar in both compartments. The ratio between the bacteria of the beta II cluster and the Actinobacteria showed a high saisonal fluctuation between the compartments. This indicates differences in their ecological role which is supported by the rapidly response of the beta-proteobacteria and a decline of the Actinobacteria to the changed growth conditions in the enrichment experiment. Measurements of extracellular peroxidase activity indicated seasonal differences between the humic rich and humic poor compartment. The activity of extracellular peroxidases was higher in the humic rich than in the humic poor compartment, with highest values during fall and winter which coincided with a high abundance of Actinobacteria.