ABSTRACT-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 pg 1-', respectively, were detected in the field when dissolved oxygen concentrations were below 3 mg I-'. Glycolaldehyde was identified as an indicator of anaerob~c degradation processes which occurred in the open water of the Elbe estuary for suspended seston aggregates 5 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 consun~ption.
From 1989From to 1992, the concentration of formaldehyde was measured along the Elbe estuary as well as at anchor stations. In mesocosm experiments, the turnover of formaldehyde could be investigated avoiding the variability caused by tidal advection of different water bodies. Formaldehyde concentrations in the Elbe estuary ranged from 0.5.. .180 pg/L. As sources, a release by algae and microbial processes were identified. Three areas with different dominance of formaldehyde turnover processes were found in the estuary. In the limnic part of the estuary, a release of formaldehyde by algae was dominant. In the mixolialine zone and the turbidity maximum, bacterial degradation of organic matter increased the formaldehyde concentration.In the mouth of the estuary, the adjacent Wadden sea areas influenced the concentration due to formaldehyde-rich runoff from the tidal mud flats. In the other parts of the estuary, a fast degradation of formaldehyde kept the formaldehyde concentration at a low level. In sediment cores from the Elbe and a mesocosm, the formaldehyde concentrations were in the same range as in the water column. Mesocosms with and without sediment showed no significant differences in concentration levels which were similar to those measured in the Elbe at the same time. During the investigated period, no anthropogenic impacts of formaldehyde into the Elbe estuary could be detected.
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