MODELING THE NITRATE FLOW IN THE GROUNDWATER PROVINCES OF THE OLD FEDERAL STATES OF THE FEDERAL-REPUBLIC-OF-GERMANY

The aim of this study is to trace the nitrate flow in the ground water from diffuse sources over the whole area of the former West Germany r anging from input into the soil up to output into surface waters. A sy stems analysis approach was selected for the implementation of these t asks since this permits an interconnection of large volumes of data wi th complex and interdisciplinary correlations. The problem-relevant as pects were compiled from the profusion of data and regularities on nit rate discharge from the soil, the hydrological and geological circumst ances as well as nitrate conversion processes in the soil and ground w ater, and pieced together to form a comprehensive model. This model wa s transformed into a computer program and coupled to a graphical progr am system permitting a clear illustration in the form of coloured grid maps. A high nitrate pollution of the ground water (> 50 mg NO3/1) ca n be expected in all regions with an intensive agricultural use of the topsoil. In particular ground-water occurrences in solid rock areas a re susceptible to nitrate pollution. There a rapid ground-water turnov er and thus a short residence time for the ground water in the aquifer is typical. Oxidizing aquifer conditions usually prevail in solid rac k aquifers preventing nitrate degradation. In many loose rock areas, i n contrast, the ground water has a low flow velocity and a long reside nce time in the aquifer. Because of a lack of free oxygen a complete d egradation of nitrate can occur, as long as iron-sulphide compounds an d/or organic carbon are available in the aquifer.