APPLICATION OF THE HBV-N MODEL TO THE BALTIC SEA DRAINAGE BASIN
A hydrochemical model, HBV-N, was set up in a first simple applicarion to simulate the river-borne transport of nitrogen to the Baltic Sea and its main basins. The land area of 1729 000 km2 was divided into 25 subbasins. The input data were coarse and the model was calibrated against long term monthly mean concentradons of inorganic and organic nitrogen. The intention was to set up a model, which can provide data to an oceanographical model for simulation of nitrogen turnover in the Baltic Sea. After calibration, the HBV-N model gave reasonable nitrogen concentrarions and transport levels. The simulation was made for the water years of 1981to 1994. A mean riverine transport to the Baltic Sea of about 660 000 tonnes of nitrogen per year, not including emissions from cities and industries along the coast, was estimated using the model. Most of the nitrogen load was inorganic. DifFuse leakage from open land was the most important source of nitrogen in the model. A considerable deal of the load from the open land came from the drainage basin of the Baltic Proper. The most critical input data were identified to be land use information and leakage concentrations, in particular for arable land