Eutrophication issues attacked by a numerical model of the North Sea/Skagerrak

Abstract

Several issues of eutrophication in the North Sea and Skagerrak have been attacked using a three dimensional ecological model, NORWECOM. The focus have been on two different years, 2000 and 2001, their characteristics and the differences between them. The results show that the annual depth integrated primary production in the whole North Sea is higher in 2001 than in 2000, but with large spatial differences. In the North Sea an extreme oxygen minimum were found in 2000 south of Dogger Bank that were not seen in 2001. Both the Atlantic inflow to the northern North Sea and the inflow through the English Channel were lower in 2001 than in 2000. Estimates from a long term modeling experiment, rank the Atlantic inflow in 2001 among the lowest since 1955, and the English Channel net flow in 2000 as the highest. The cross boundary flow of inorganic nitrogen from the German Bight to the Skagerrak was 50% higher in 2000 than in 2001. An eutrophication assessment from the modeled N/P ratio gives significant higher levels in 2000. The effect on this level is also documented from a reduced input of inorganic nitrogen in the river waters.