SEDIMENT-WATER NUTRIENT FLUXES IN THE GULF OF FINLAND, BALTIC SEA

High nutrient inputs from the Neva River in the eastern Gulf of Finlan d, Baltic Sea create steep spatial gradients in water column concentra tions of nutrients and of particulates. During July 1993 nun-lent flux es 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 c oncentrations were depleted within the first 2-4 mm of the sediment-wa ter interface and calculated O-2 consumption ranged from -462 to -526 mu mol m(-2) h(-1) with no significant differences [analysis of varian ce (ANOVA); P>0.05] observed between stations. Spatial patterns, howev er, were evident with significant differences between stations observe d in most nutrient fluxes (ANOVA; P<0.01) with the highest sediment-wa ter 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 m ol m(-2)h(-1) for NO2- and 1.59-28.5 mu mol m(-2)h(-1) for dissolved i norganic phosphate. Dissolved silicate Awes (71.8-83.5 mu mol m(-2)h(- 1)) were the only nutrient not to show significant differences (one-wa y ANOVA; P>0.05) between stations. Estimated denitrification rates fro m sediments ranged from 6.6-11.5 mu mol m(-2)h(-1) and are not particu larly intense compared with other Baltic areas, however, given that th ese rates only include denitrification supported by water column NO3- concentrations and not denitrification coupled to nitrification with t he 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 sedi ment-water Awes reported here include some of the highest rates report ed for the Baltic Sea, but are typical of most eutrophic coastal marin e environments. The high fluxes reported here contribute to the large reservoir of dissolved inorganic nutrients contained in the water colu mn immediately below the mixed surface layer. (C) 1997 Academic Press Limited.