GeoAPEXOL, a web GIS interface for the Agricultural Policy Environmental eXtender (APEX) model enabling both field and small watershed simulation

Nonpoint source (NPS) pollution is a common problem faced in many places around the world. On-site evaluation of NPS pollution is helpful in deciding how serious the pollution is and where a controlling practice can potentially be implemented with the best effectiveness. In this study, a web GIS interface for the Agricultural Policy Environmental eXtender (APEX) model named GeoAPEXOL was developed. The interface serves as a tool to automatically setup the APEX model for a watershed or field and conduct a rapid evaluation of the NPS pollution. A background database including DEM, landuse, soil, climate, and agricultural management was prepared for automating the process of model setup. One important feature of the interface is that NPS pollution can be evaluated for a field boundary considering contribution from upstream areas, which may be located outside the field boundary and is generally ignored by traditional NPS evaluation methods at the field scale.