Integrated modelling of oxygen deficits in the Danish marine area

Abstract

A model has been developed with the focus of describing the oxygen deficits in the bottom water of the Danish marine area. This area is divided into the Western Baltic, the Belts and the Kattegat. The freshwater from the Baltic Sea gives a brackish water mass, which leaves the area in the top of the water-column, and creates a bottom inflow of saline water originating from the Skagerrak. Measurements of the salinity, wind and current were used to set up a hydrodynamic flow submodel. On top of this model a nitrogen source model was added. The model quantifies the nitrogen sources to the upper layers into runoff from the land, atmospheric deposition, input from the Baltic Sea, the pool of nitrogen at the start of the period and entrainment from the bottom layers, which is the biggest source of all. The results show that the year to year variation in the oxygen concentrations over the period 1980–1987 can be described as a function of the nitrogen input and pools, and contemporaneous weather conditions. The study shows also that an integration between modelling and monitoring is necessary to achieve predictive tools. The model is validated towards independent data from 1988–1989.