Assessment of eutrophication in Skagerrak coastal waters using oxygen consumption in fjordic basins

Abstract

The mean rates of oxygen consumption have been estimated for 9 different fjordic sill basins in 1990 on the Norwegian Skagerrak coast. The mean oxygen consumption rate was about 50% higher than in similar basins on the west coast of Norway. The observations are in accordance with an empirical model from the Norwegian west coast, where mean oxygen consumption rate in sill basins is derived as a function of sill depth and mean basin depth. Historical oxygen observations suggest that increased oxygen consumption occurred in the first part of the 1980s. Due to intensive water exchange above sill level and insignificant influence of local inputs of anthropogenic nutrients, increased oxygen consumption in the sill basins is most likely to be related to increased large scale eutrophication of the Skagerrak coastal waters. The natural low oxygen concentrations in many sill basins along the Skagerrak coast make them particular sensitive to increased oxygen consumption.