Organic matter degradation through respiration in littoral and pelagial including profundal zones of an oligotrophic lake assessed by electron transport system activity

The intensity of respiratory carbon loss through respiration, assessed by respiratory electron transport system (ETS) activity, was studied in net zooplankton, microplankton, zoobenthos, macrophytes and sediment in the littoral and pelagial including profundal zone of Lake Bohinj over a complete year. The contributions of these components to the total metabolic activity in a particular zone of the lake were compared and the relationship between the contributions of littoral and pelagial including profundal respiratory carbon loss and the estimated assimilated carbon in phytoplankton and macrophytes was determined. The greatest areal (m(-2)) carbon loss was observed through sediments in the littoral zone which, on average, contributed 97.6% to total carbon loss in the littoral compartment of the lake. Significantly lower values were observed in this zone for zoobenthos (1.2%), microplankton (0.9%), macrophytes (0.2%) and zooplankton (0.1%). In the combined pelagial and profundal zone, sediments contributed 78.8% to the total carbon loss. Lower values were observed in microplankton (13.4%), followed by zooplankton (7.0%) and zoobenthos (0.8%). Total areal respiratory carbon loss in the littoral significantly exceeded that in the pelagial including profundal zone, but the littoral zone and the pelagial including profundal zone made similar contributions of respiratory carbon loss to whole-lake metabolism. Whole-lake respiratory carbon loss through zooplankton, microplankton, zoobenthos, sediments and macrophytes exceeded the estimated carbon productivity of phytoplankton and macrophytes. The latter was greater in littoral than in pelagial including profundal. In littoral, macrophytes contribute significantly to carbon productivity, but less to respiration, while sediment contributed the greatest part of respiration in both littoral and pelagial including profundal.