Modeling non-point source pollutants in soil: Applications to the leaching and accumulation of pesticides and cadmium

The general objective of the present study was to contribute to a justified application of plot-scale developed models of non-point source pollutants on a regional-scale. Two environmental issues were studied, i.e. the leaching of pesticides to the shallow groundwater and the accumulation of cadmium in the topsoil and leaching into the groundwater. These two issues were chosen because they required entirely different model approaches. Pesticide leaching was calculated with a detailed, numerical, multi-layer model with a high temporal resolution (PESTRAS). Processes included were transient flow, convection, hydrodynamic dispersion, equilibrium sorption, degradation, uptake by plant roots and volatilization. In the heavy metal accumulation study two models were used: A comprehensive, multi-layer, numerical model (METRAS), which was applicable at the plotscale, and a simple analytical, one-layer model with a lower temporal resolution (SOACAS), which was used for the regional-scale assessments. Processes included in SOACAS are steady-state waterflow, convection, equilibrium sorption, complexation, and plant-uptake.