BENTHIC BACTERIAL PRODUCTION AND NUTRIENT SEDIMENT-WATER EXCHANGE IN SANDY NORTH-SEA SEDIMENTS

The relationship between benthic bacterial production and biomass and sediment-water exchange rates of inorganic nutrients was examined in t he North Sea (Dogger Bank region), in summer. The sediments were sandy , poor in organic matter and with low buffering capacities for nutrien ts. Fluxes of dissolved inorganic N (DIN) and P (DIP) across the sedim ent-water interface were measured using undisturbed sediment cores. Ba cterial production (H-3-thymidine incorporation method) in the sedimen t surface layer and bacterial biomass were analysed in the same sedime nt. By comparison of the benthic activities at 13 stations we assessed significant negative relations between bacterial production and sedim ent-water fluxes of nutrients. With increasing bacterial production th e net efflux of DIN and DIP decreased. Bacterial production was signif icantly related to bacterial biomass and bacterial biomass was signifi cantly related to chlorophyll a and pheopigment in the sediment, sugge sting that enhanced bacterial production rates were associated with in put of organic carbon. The observed relationship between bacterial pro duction and nutrient sediment-water exchange could be explained by tem porary immobilization of N and P in bacterial biomass. It was demonstr ated that in response to a short-term sedimentation event, the increas e in benthic bacterial biomass (over a 5 d period) may equal the decre ase in sediment-water effluxes of DIN and DIP. Heterotrophic benthic b acteria can apparently act as sinks for N and P, which only release N and P upon death.