The role of plankton, zoobenthos, and sediment in organic matter degradation in oligotrophic and eutrophic mountain lakes

Abstract

Intensity of organic matter degradation, assessed by the respiratory electron transport system (ETS) activity, was studied in microplankton, zooplankton, chironomid larvae as the dominant group of the macrobenthos, and sediment in mountain lakes of different trophic levels in summer months. The highest ETS activities per unit of surface were observed in sediments. Significantly lower activities were observed in microplankton, and lower still in zooplankton, and chironomids. The total ETS activity m−2 was higher in eutrophic lakes (Jezero na Planini pri Jezeru and Krnsko jezero) than in oligotrophic ones (Zgornje Krisko jezero, Spodnje Krisko jezero, Jezero v Ledvicah). The contributions of communities investigated to total ETS activity m−2 differed between lakes of different trophic level. Estimation of respiratory carbon loss through different components revealed that the most of the organic matter was oxidized in sediments of mountain lakes. The respiratory carbon losses were higher through zooplankton than through microplankton in all lakes. Carbon losses through plankton components and sediments were significantly lower in oligotrophic than in eutrophic lakes. The contribution of respiratory carbon loss through chironomids to total carbon loss m−2 was higher in oligotrophic than in eutrophic lakes. Therefore, it seems that contributions of microplankton and zooplankton to mineralization processes increase, and contributions of chironomids and sediment surface decrease with increasing trophic level of the lakes.