Improved PADDY-Large model including lateral seepage loss from paddy fields to predict pesticide behavior in river basins.

We developed an improved simulation model for predicting pesticide concentrations in river basins based on PADDY-Large, which includes lateral seepage loss of pesticides from paddy fields. Based on the structure of typical Japanese paddy fields, pesticide transport process due to lateral seepage through bunds was modeled as a compartment system consisting of pore water and soil particle. The model was validated with concentrations measured by monitoring paddy pesticides in a tributary of the Sakura River in Japan. The improved model by including loss of pesticides due to lateral seepage through bunds successfully simulated temporal changes in the pesticide concentrations.