Microbial activities in estuarine sediments (Ebro Delta, Spain) influenced by organic matter influx
S. Mallo, F. Vallespinós, S. Ferrer and D. Vaqué

Bacterial activities and biomass in sediments at two stations (Sta. 2 and Sta. 3) in Alfacs Bay, Ebro Delta. Spain were determined on a monthly basis, from April 1986 to March 1987. Maximal respiratory activity (aerobic and anaerobic) was highest in summer, which implied active transformation of accumulated organic matter in the sediment. This accumulation of organic material was always higher at Sta. 2 (average: 77 mg g-1).than at Sta. 3 (average: 16 mg g-1) due to the proximity of freshwater allochthonous inputs. In Sta. 2 we observed temporal changes in the activities of bacterial functional groups implying a succession in time of different electron acceptors. e.g., from the use of molecular O2 to NO3 and, eventually, to SO4, as the redox potential decreased. Maximum rates of oxygen consumption, heterotrophic activity, denitrification and the presence of anoxic sediments occurred at the end of summer. These sediment conditions should favour the development of sulphate reducing bacteria and their participation in the global flow of electrons. Sta. 3 always showed lower values of bacterial activities and biomass than Sta. 2, as well as positive redox potential. Averages of oxygen consumed along the year were 1.12 mmol O2 g-1 d-1 at Sta. 2 and 0.37 mmol O2 g-1 d-1 at Sta. 3. Denitrification rates averaged 147.87 nmol N2 g-1 d-1 at Sta. 2 and 50.73 nmol N2 g-1 d-1 at Sta. 3, and heterotrophic activity averages were: 0.037 nmol 3H thymidine g-1 h-1 at Sta. 2, and 0.012 nmol g-1 h-1 at Sta. 3. Bacterial biomass (heterotrophs, denitrifiers, and sulphate reducing bacteria) presented values one or two orders of magnitude higher at Sta. 2 than at Sta. 3. Our results showed that the development of bacterial communities changed with time at these two stations, depending on the proximity of external inputs of organic material.

Keywords: Microbial activities, allochthonous inputs. seasonal variations. estuarine sediments, Ebro Delta.
Contents of this volume Sci. Mar. 57(1) : 31-40 Back PDF
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