Development of a GIS method to localize critical source areas of diffuse nitrate pollution

The present study aimed at developing a universal method for the localization of critical source areas (CSAs) of diffuse nitrate (NO₃⁻) pollution in rural catchments with low data availability. Based on existing methods, land use, soil, slope, riparian buffer strips and distance to surface waters were identified as the most relevant indicator parameters for diffuse agricultural NO₃⁻ pollution. The five parameters were averaged in a GIS-overlay to localize areas with low, medium and high risk of NO₃⁻ pollution. A first application of the GIS approach to the Ic catchment in France, showed that identified CSAs were in good agreement with results from river monitoring and numerical modelling. Additionally, the GIS approach showed low sensitivity to single parameters, which makes it robust to varying data availability. As a result, the tested GIS-approach provides a promising, easy-to-use CSA identification concept, applicable for a wide range of rural catchments.