NUTRIENT (P,N) DYNAMICS IN THE SOUTHWESTERN KATTEGAT, SCANDINAVIA SEDIMENTATION AND RESUSPENSION EFFECTS

The yearly nutrient supply from land and atmosphere to the study area in SW Kattegat is 10 900 tons of N and 365 tons of P. This is only few percent of the supply from adjacent marine areas, as the yearly trans port through the study area is 218 000 tons of N and 18 250 tons of P. Yearly net deposition makes up 1340 tons of N (on average 2.5 g m(-2) yr(-1)) and 477 ton of P (on average 0.9 g m(-2) yr(-1)). Shallow-wat er parts of the study area have no net deposition because of frequent (> 35% of the year) resuspension. Resuspension frequency in deep water is < 1% of the year. Resuspension rates, as averages for the study ar ea, are 10-17 times higher than net deposition rates. Because of resus pension, shallow-water sediments are coarse lag deposits with small am ounts of organic matter (1.1%) and nutrients (0.04% N and 0.02% P). De epwater sediments, in contrast, are fine grained with high levels of o rganic matter (11.7%) and nutrients (0.43% N and 0.15% P). Laboratory studies showed that resuspension changes the diffusive sediment water fluxes of nutrients, oxygen consumption, and penetration into the sedi ment. Fluxes of dissolved reactive phosphate from sediment to water af ter resuspension were negative in organic-rich sediments (13.2% organi c matter) with low porosity (56) and close to zero in coarse sediments with a low organic matter content (2.3%) and high porosity (73). Flux es of inorganic N after resuspension were reduced to 70% and 0-20% in relation to the rates before resuspension, respectively.