Gerold Hepp , Eva Strenge, Matthias Zessner

This study presents an algorithm for the allocation of particulate phosphorus (PP) loads entering surface waters to their sources of origin, which is a basic requirement for the identification of critical PP source areas and in turn a cost-effective implementation of mitigation measures. Furthermore, it conducts a sensitivity analysis determining the impacts of storm drains, discharge frequencies and flow directions on the designation of critical source areas with the help of present-day scenarios for a case study catchment with an area of several hundred square kilometres. The results show that the scenarios at least partially disagree on the identified critical source areas and suggest that especially open furrows at field borders have the potential to cause deviating critical source areas. Finally yet importantly, the Particulate PhozzyLogic Index based on model results as well as fuzzy logic is introduced. Its main feature is to transform the results of diverse scenarios or even models into a final map showing a catchment-wide ranking of the possibility of high PP emissions reaching surface waters for all agricultural fields.