Sediment-water nutrient fluxes in the Gulf of Finland, Baltic Sea

High nutrient inputs from the Neva River in the eastern Gulf of Finland, Baltic Sea create steep spatial gradients in water column concentrations of nutrients and of particulates. During July 1993 nun-lent fluxes across the sediment-water interface were measured beginning in this eutrophication gradient and extending out into the open waters of the western Gulf. Dissolved oxygen (O-2) microgradients showed that O-2 concentrations were depleted within the first 2-4 mm of the sediment-water interface and calculated O-2 consumption ranged from -462 to -526 mu mol m(-2) h(-1) with no significant differences [analysis of variance (ANOVA); P>0.05] observed between stations. Spatial patterns, however, were evident with significant differences between stations observed in most nutrient fluxes (ANOVA; P<0.01) with the highest sediment-water fluxes observed at the most eutrophic station in the eastern Gulf of Finland. Sediment-water fluxes ranged between 9.37-34.7 mu mol m(-2)h(-1) for NH4+, -6.8-12.45 mu mol m(-2)h(-1) for NO3-, 0.10-2.45 mu mol m(-2)h(-1) for NO2- and 1.59-28.5 mu mol m(-2)h(-1) for dissolved inorganic phosphate. Dissolved silicate Awes (71.8-83.5 mu mol m(-2)h(-1)) were the only nutrient not to show significant differences (one-way ANOVA; P>0.05) between stations. Estimated denitrification rates from sediments ranged from 6.6-11.5 mu mol m(-2)h(-1) and are not particularly intense compared with other Baltic areas, however, given that these rates only include denitrification supported by water column NO3- concentrations and not denitrification coupled to nitrification with the sediments, then they are not so far from the rates (17.8 mu mol m(-2)h(-1)) estimated from mass balances in the Gulf of Finland. The sediment-water Awes reported here include some of the highest rates reported for the Baltic Sea, but are typical of most eutrophic coastal marine environments. The high fluxes reported here contribute to the large reservoir of dissolved inorganic nutrients contained in the water column immediately below the mixed surface layer. (C) 1997 Academic Press Limited.