DYNAMICS OF CU RELEASE DURING EARLY AEROBIC DEGRADATION IN AGGREGATEDSESTON FROM THE ELBE ESTUARY

Using a new laboratory device, the mobilization of Cu, Cd, and Pb was monitored continuously by analysing the water overlying and underlying a approximate to 1 mm seston layer using voltammetric methods. The mi neralization of organic matter was quantified by the heterotrophic oxy gen consumption. The CO2 formed was analysed for its C-13-content to c haracterize the organic C-pool used in degradation. Changes in the bio chemical composition of the particulate material were determined at th e beginning and end of an aerobic incubation period. Heterotrophic pro cesses were initiated about 20 h after settling of the seston. The agg regated seston became refractory for aerobic microbial degradation aft er about 120 h of aerobic incubation. At this stage nitrification agai n balanced the total oxygen consumption. The mineralization of the org anic matter was between 7.7 and 17.4% of the total and 62-75% of this consisted of dying algal biomass. A significant release of Cu from the seston layer was restricted to a period of about 40 h and was correla ted to the period when a limitation of heterotrophic processes by orga nic substrates occurred. Then, Cu concentrations increased to between 8 and 28 nM in the water overlying the layer that equalled a mobilizat ion rate of between 0.24 and 0.94 (nmol/cm(2) d). Cd and Pb did not sh ow a similar pattern and were detected at concentrations of always bel ow 2 nM. Deeper parts of the layer functioned as a sink for Cu at oxyg en concentrations of less than or equal to 25 mu M and concentrations of Cu in the water underlying the seston layer remained below 1.5 nM. During periods of short-term release Cu in solution accounted for betw een 3 and 10% of the total particulate Cu. The results suggest that a significant amount of the Cu within the seston material was retained i n the protein fraction of the algal matter and is released into the ov erlying water during its aerobic degradation.