Concentration and bacterial utilization of sub-micron particles and dissolved organic carbon on lakes and a coastal area

The distribution of organic carbon among dissolved organic carbon (DOC, 0,7 μm) was studied in a number of aquatic systems differing in trophic status and humic content. COC and POC were positively conelated and found in equal concentrations. The relative contribution of COC to total dissolved organic matter (DOM, < 0,7 μm) tended to increase with increasing DOC concentration and constituted from 3 to 30 % of total DOM (i.e. DOC + COC). This indicated an increase in the quantitative importance of sub-micron particles with increased productivity of the systems. Labile COC concentration, estimated in long-term bacterial decomposition experiments, varied between 62 and 371 μg C1 −1 , and constituted from 12 to 45 % of total DOM lability. Bacterial COC utilization generally occuned during the last part of the incubations by use of bacterial extracellular enzymes. It was suggested that significant bacterial COC degradation in natural systems are limited to periods of low input rates of easily available substrates