MODELING THE FLOW OF NITROGEN AND PHOSPHORUS IN EUROPE - FROM LOADS TO COASTAL SEAS

A model is described that aims at predicting surface water quality fro m N- and P-inputs on a European scale. The model combines a GIS-based approach to estimate loads, geohydrological data to define model struc ture and statistical techniques to estimate parameter values. The mode l starts with an inventory of sources of N and P: agriculture, wastewa ter and (for N) atmospheric deposition. Nitrogen flows are assumed to follow both surface- and groundwater flows, while for phosphorus only surface water flow is taken into account. A calibration of loss terms of N and P (assumed to be constants for the whole of Europe) by compar ing total inputs to measured loads shows good agreement between observ ations and calculated river discharges. For the coastal seas of Europe concentrations are calculated by assuming conservative behaviour of N and P. Freshwater quality problems occur in western Europe with its i ntensive agriculture and high population density and locally in southe rn Europe where dilution is low due to low water discharge. In the mar ine environment the main problem areas are the Baltic and Black seas, with much lower impacts in the North and Adriatic Sea; in other coasta l waters human impacts are essentially negligible.