Nutrient exchange across the sediment–water interface in the eastern Gulf of Finland

Benthic nutrient fluxes (sedimentation, degradation and burial within the sediment, and release to the water column) were estimated for a series of stations in the Neva Bay and different areas of the eastern Gulf of Finland (GOF). It was shown, that the Gulf sediments act as an efficient trap for both nutrients: 20%–50% of P and 40%–65% of N in the Neva estuary and in the open Gulf, and up to 100% in the Neva Bay are buried within the accumulating sediment. The rest is released to the overlying water. Minor portion of dissolved nutrients is released by molecular diffusion from the deep sediment layers. The diffusion from immediate sediment-water interface and convective transport seem to be of greater importance in nutrient release. The variations in the intensity of benthic processes of nutrient sedimentation, adsorption, minerals formation, nitrification, denitrification and convective transport from the sediments in the sub-areas of the Gulf are generally determined by the chemical composition and amount of sedimenting material, in combination with bottom dynamics. Benthic nutrient flux to the overlying water could supply generally a small fraction of estimated phytoplankton nutrient demand (0%–10% of P and 1%–5% of N).