Modeling pesticide leaching at field-to-regional scale using an integrated GIS/solute transport approach

Non-point source pollution (NPS) is a major environmental problem that exists over multiple scales. Field experimentation to assess leaching and transformation of NPS is limited by the difficulties involved in obtaining field measurements at the required scales. Solute transport models are widely used to predict NPS pollutants especially at the watershed scale. Transport models are linked with a geographic information system (GIS) to allow for a better representation of the spatial variability found in soils and to enhance and facilitate the analysis and representation of the large amount of spatial data associated with NPS pollution.; In this study, a regional scale soils database was compiled at three different hierarchical scales, and a mechanistic solute transport model was linked through GIS to the soils database to evaluate pesticide leaching at the watershed scale. A methodology to extract and average soil properties and to estimate soil hydraulic properties based on pedo-transfer functions was presented. Spatial variability and the effect of scaling from field to regional scale was investigated. In general, more atrazine leaching was observed under transient as compared to steady-state flow. Leaching was dominated by soils with low organic matter and thin A horizons. Scaling was possible between the two smaller-scale watersheds. The approach presented is limited by several assumptions and simplifications. Lateral movement and macropore flow were not considered in the simulation; nevertheless, the simulations predicted the susceptibility of leaching pesticides under the assumption of vertical flow. The linkage between transport models and GIS proved to be a useful approach to identify areas with higher potential for leaching problems.