Simulation of soil water, bromide and pesticide behaviour in soil with the GLEAMS model

The GLEAMS model predicts runoff, percolation and soil and chemical losses at the edge of a field and from the root zone. The objective of this study was to test the performance of the GLEAMS model against three observed data sets from different parts of Europe. Three users tested the model independently, i.e. parametrized the model without discussion with the other users. Both uncalibrated and calibrated results are presented. Furthermore, the pesticide sub-model was parametrized according to proposals of the supplier of the measurement data. The test was focused on soil moisture, tracer (bromide) and pesticide movements in soil columns. The results show that GLEAMS soil moisture predictions appear to react too rapidly to wet and dry periods, resulting in a rapid change of soil moisture between field capacity and wilting point. Incomplete simulation of soil water dynamics seems to be the main reason for underestimation of tracer movement in soil. In addition, mismatches in soil pesticide concentrations might be caused by incorrect prediction of degradation processes. The results of the independent users differed considerably from each other, both in uncalibrated and in calibrated results, due to different interpretation of the measured data.