Abstract

Estimates are needed to assess the vulnerability of the soils in the Netherlands to pesticide leaching. The most important processes determining the ultimate fate of pesticides are degradation, sorption, uptake and transport. As the interaction between these processes is complex and non-linear, the use of a process oriented, dynamic simulation model in prediction and spatial interpolation is indispensible. The model must meet the following requirements: (i) it must have a modular set-up to facilitate model development and maintenance, (ii) it must be easy to link the model to an external environment, in particular GIS, (iii) the model must be applicable to all relevant major combinations of soil type, land use and pesticides and (iv) the model must confirm to high quality standards with respect to design, documentation, validation and configuration management. In this context, the dynamic process oriented model PESTRAS was developed at RIVM. The model is built from existing submodels, i.e. the soil water transport submodel SWIF, the heat transport submodel of ILWAS and the pesticide leaching and accumulation model PESTLA. The existing submodels were adapted to meet the above mentioned requirements. This report summarizes the model principles, describes the numerical scheme, provides guidelines for model use, gives examples of model output for a case study on a maize plot on a sandy soil and describes the results of a sensitivity analysis. The method for regionalization and the data derivation for this purpose will be described in a seperate report.