Modelling and mapping pesticide exposure risk at the catchment scale (MOMAPEST)

A quantitative description of the fate of pesticides in the aquatic environments is very complex. Models are needed to give realistic evaluations of pesticide exposure of streams and groundwater at the landscape level. Complex, fully distributed models with great demands on input data have been tested in Denmark to describe transport of pesticides in streams in Denmark without satisfactory results. The project tested the ability of the semi-distributed SWAT model to quantify and visualize pesticide exposure of groundwater and surface water from small scale to landscape scale. SWAT is a freely available, open-source eco-hydrological catchment model that flexibly can be adapted to the available input data. A new module for SWAT describing the transport of dissolved and particulate bound pesticides via macro-pores to tile drains was developed. The model was used to produce maps of pesticide exposure for the island of Fyn subdivided into 102 sub-basins for the pesticides Bentazone, Primicarb and Propiconazol. Scarcity of local pesticide measurements hampered a proper validation of the modelling results. However, a comparison to all available pesticide measurements in Danish streams indicated that modelling results are in the right order of magnitude for all three test pesticides. Thus, despite the uncertainty surrounding model predictions, the SWAT model may be a useful tool for assessing the risk of pesticide exposure of surface waters at landscape level. Regarding groundwater, the project concluded that SWAT at its current development stage is not useful for decision-making or to inform policy on the risk of pesticides exposure.