Pesticide Transport Models: Comparison and Validation with Soil Column Leaching Experiments

Computer models to simulate pesticide transport in the unsaturated zone will be an important management tool in coming years. However, not many efforts were directed to validate the usefulness of such models. In this study, the simulation models GLEAMS, PRZM, and LEACHM were validated. The three models use different mathematical concepts to compute one-dimensional flow and transport in a homogeneous, unsaturated soil. In laboratory experiments, the two pesticides atrazine and terbuthylazine and a conservative tracer were applied to four different soils packed in stainless steel columns. The breakthrough curves obtained from the steady-state unsaturated leaching experiments were compared to the modeling results. The model simulations were based on standard laboratory measurements of the physical and chemical soil-pesticide properties of the sample soils and pesticides. The three models predicted solute breakthrough in general within a factor of two of the measured breakthrough curves. Among the three models, PRZM and LEACHM performed best, while GLEAMS computations are fast at the cost of accuracy.