Sediment studies in the Stockholm archipelago 2008
A clear indication of improved benthic conditions was found when sediment investigations from the 1990s were repeated in the inner Stockholm archipelago during 2008. In a majority of the investigated areas the surface sediments were oxidized and signs of bioturbation were observed. In the 1990s these areas were dominated by black and laminated surface sediments. When comparing the interpretation of sediment status versus macrozoobenthos data a clear congruence was found. The magnitude of sediment phosphorus (P) turnover in the Stockholm archipelago was closely linked to the sediment accumulation rate. Improvement of the oxygen status in the surface sediment layer have resulted in a temporary accumulation of iron (Fe) bound P. This P might reach high concentrations, and represents a withdrawal of P that otherwise would support primary production. Whether this Fe-P mainly did precipitate in the water column and did settle to the sediment, or if it formed in the oxygenated surface sediment layer due to diffusion of dissolved P and Fe from deeper sediment layers remains uncertain.