DIAGENETIC PROCESSES AND NUTRIENT FLUXES AT THE SEDIMENT-WATER INTERFACE, NORTHERN ADRIATIC SEA, ITALY

Early diagenetic processes that control pore-water chemistry and nutri ent fluxes at the sediment-water interface were studied in late summer 1989 and spring 1990 at four sites influenced by fine sediments of th e Po River. Parameters on the solid fraction (grain size and C, N and P) and pore-water profiles of SO42-, NO3-, NH3, alkalinity, PO43-, Fe, Mn, Ca and Mg were determined. Data interpretation was supported by a pplication of kinetic and stoichiometric modelling. Nutrient fluxes we re calculated by Fick's first law. In the prodelta station the pore-wa ter profiles showed large depletion in SO42- ions, jointly with the in crease with depth of alkalinity, NH3 and PO43- concentrations, thus in dicating anaerobic decomposition of organic matter, mainly due to bact erial sulfate reduction. At the other three sites the results were com pletely different. Nutrient concentrations in pore water were one orde r of magnitude lower. The peaks of alkalinity, NH3 and PO43- values ne ar the interface and the constant presence of SO42- ions indicate aero bic decomposition of organic matter in the uppermost sediment. Nutrien t fluxes showed much higher values in the prodelta station, whereas fl uxes in the remaining stations decreased southward. In addition, seaso nal variations produced higher summertime fluxes. The clear-cut differ ence in diagenetic processes as a function of the distance from the ma in Po River mouth can be explained by the rapid burial of sediments ri ch in organic matter and inorganic compounds in the prodelta station. At the other stations, the lower sedimentation rate and more efficient bioturbation and resuspension processes cause a prolonged exposure of sediments to aerobic metabolization reactions before burial.