Seasonal patterns of sedimentary carbon and anaerobic respiration along a simulated eutrophication gradient

Concentrations of organic carbon and rates of dissimilative sulfate reduction in surface sediments of marine mesocosms were examined along an experimental eutrophication gradient. Phytoplankton biomass increased due to addition of inorganic nutrients (N. P, Si). This increase was especially pronounced during the winter spring diatom blooms, which increased in magnitude and duration along the nutrient gradient. Net system production in winter and spring resulted in carbon deposition and accumulation in surface sediments (maximum net accumulation 17 mol C m-2). Benthic remineralization of carbon exceeded depositional supply during summer and fall. Sediment carbon concentrations approached background levels in December and February, suggesting very little annual accumulation of sediment carbon Sediment oxygen consumption and sulfate reduction rates both increased as a result of carbon sedimentation. Sulfate reduction rates in organic enriched sediments were an order of magnitude higher than control and were correlated with temperature and carbon concentrations (r2 = 0.85). Anaerobic respiration rates in unenriched sediments were related only to seasonal patterns of temperature (r2 = 0.70). Anaerobic metabolism was the dominant metabolic pathway in control and treated sediments, with 50 to 70% of annual carbon remineralization due to sulfate reduction

A carbon budget for a eutrophic marine ecosystem and the role of sulfur metabolism in sedimentary carbon, oxygen and energy dynamics

Organic carbon was budgeted for an experimental marine ecosystem which received 21.2 mol C m–2 of allochthonous sewage sludge plus 12.4 mol C m–2 in situ net daytime production over a 99 day experiment. The fate of carbon, in order of importance, was remineralization, storage in the sediments and export. Sediment carbon metabolism was dominated by sulfate reduction which resulted in the dissociation of organic carbon remineralization from oxygen consumption and energy cycling. The sediments were inefficient in processing sedimented carbon and its associated chemical energy. About 70% of the energy reaching the sediments as organic carbon remained as accumulated carbon and sulfide minerals at the end of the experiment (71% of remaining energy was in the form of unrespired C and with the remaining 29% of energy stored as precipitated sulfides). Sediment oxygen consumption was a poor estimator of benthic metabolism. Total CO2 flux from the sediments was, however, balanced by the sum of sediment oxygen consumption plus oxygen equivalents stored as sedimentary sulfides. Sludge additions drove the experimental ecosystem to a eutrophic state with periods of severe oxygen depletion, death of macrofauna, hydrogen sulfide concentrations in excess of 1 mmolar in surface sediments, and the presence of a white filamentous bacterial mat over the sediment surface

A carbon budget for a eutrophic marine ecosystem and the role of sulfur metabolism in sedimentary carbon, oxygen and energy dynamics

Organic carbon was budgeted for an experimental marine ecosystem which received 21.2 mol C m-2 of allochthonous sewage sludge plus 12.4 mol C m-2 in situ net daytime production over a 99 day experiment. The fate of carbon, in order of importance, was remineralization, storage in the sediments and export. Sediment carbon metabolism was dominated by sulfate reduction which resulted in the dissociation of organic carbon remineralization from oxygen consumption and energy cycling. The sediments were inefficient in processing sedimented carbon and its associated chemical energy. -from Author

Bacterioplankton dynamics in the Mondego estuary (Portugal)

In this work, the density of bacterioplankton and environmental parameters were monitored over a 11 month period (July 1999-June 2000), and also during one tidal cycle (15 June 2000), at two sampling stations, in the estuary of River Mondego. These data were treated by multivariate analyses methods in order to identify the key factors that control the dynamics of the bacterioplankton in the estuary. Bacterial dynamics were dominated by temporal gradients (annual seasons and tide-related) and less by the spatial structure of the estuary. Three main metabolic groups of bacterioplankton--aerobic heterotrophic bacteria, sulphate-reducing bacteria (SRB) and nitrate-reducing bacteria (NRB)--involved in the cycling of organic matter, were present in the water column of the estuary. Their relative abundance depended on the particular physical, chemical and biological environment. The abundance of aerobic heterotrophic bacteria, during the 11 month study, was modelled as a function of nitrate (the most important variable, with a negative effect), temperature, salinity and pH (with positive effects). SRB appeared to be limited to the water-sediment interface, where concentrations of sulphate and POM were greater. A competition between SRB and NRB for carbon has also been suggested.http://www.sciencedirect.com/science/article/B6VR3-4B6JTC7-8/1/1f5b2e8bcb56fdceb5fffe6f34b30e3