Modelling the flow of nitrogen and phosphorus in Europe: From loads to coastal seas

A model is described that aims at predicting surface water quality from N- and P-inputs on a European scale. The model combines a GIS-based approach to estimate loads, geohydrological data to define model structure and statistical techniques to estimate parameter values. The model starts with an inventory of sources of N and P: agriculture, wastewater 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 comparing total inputs to measured loads shows good agreement between observations 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 intensive agriculture and high population density and locally in southern Europe where dilution is low due to low water discharge. In the marine environment the main problem areas are the Baltic and Black seas, with much lower impacts in the North and Adriatic Sea; in other coastal waters human impacts are essentially negligible.