MEPS 123:281-293 (1995)  -  doi:10.3354/meps123281

Early microbial degradation processes and accumulation of carbonyl compounds and carboxylic acids in seston aggregates under oxic and suboxic environmental conditions were studied. In laboratory experiments, aerobic decomposition of seston material increased after aggregation and maximum rates were reached after about 70 h. Seston material that became refractory to aerobic degradation was mineralized anaerobically with nitrate as the terminal electron acceptor at a rate amounting to about 50% of the maximum rate during the previous aerobic incubation. During both early aerobic and anaerobic degradation of seston, a decrease in particulate organic carbon (POC) and the C:N ratio was observed. A net production of glyoxylate and glycolaldehyde occurred under anaerobic heterotrophic conditions and concentrations up to 4 and 30 ug l^-1, respectively, were detected in the field when dissolved oxygen concentrations were below 3 mg l^-1. Glycolaldehyde was identified as an indicator of anaerobic degradation processes which occurred in the open water of the Elbe estuary for suspended seston aggregates <=2 mm in diameter. Results indicate a strong coupling between aerobic and anaerobic processes in the aggregates whereby anaerobic net production of DOC could significantly enhance O₂ consumption.

Suspended matter . Nitrification . Oxygen and nitrate respiration . Degradation . DOC . Anaerobic conditions . Elbe estuary