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

Authors: FENG, QINGYU - Purdue University; Flanagan, Dennis; ENGEL, BERNARD - Purdue University; YANG, LEI - Chinese Academy Of Sciences; CHEN, LIDING - Chinese Academy Of Sciences

Submitted to: Environmental Modelling & Software
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/25/2019
Publication Date: 10/25/2019
Citation: Feng, Q., Flanagan, D.C., Engel, B., Yang, L., Chen, L. 2019. GeoAPEXOL, a web GIS interface for the Agricultural Policy Environmental eXtender (APEX) model enabling both field and small watershed simulation. Environmental Modelling & Software. 123:104569. https://doi.org/10.1016/j.envsoft.2019.104569.
DOI: https://doi.org/10.1016/j.envsoft.2019.104569

Interpretive Summary: Runoff from agricultural fields can transport a wide range of pollutants, including sediment, nutrients, and pesticides from cropped areas. While knowledge about the amount of flow and pollutants leaving a site is very important for planning conservation practices or doing other environmental assessments, measurement in the field is difficult, costly, and impractical for large areas. Instead, computer simulation models are often applied that simulate the effects of climate (rain storms, temperatures), topography (slope length and steepness), soils (infiltration, runoff generation, erodibility), and cropping/management practices (crop rotations, tillage systems, etc.) on runoff, tile flow, soil erosion, and chemical losses. One current USDA-ARS tool used for these types of applications is the Agricultural Policy Environmental eXtender (APEX) model. While this model provides good estimates of runoff and pollutant losses, it can be difficult to apply by ordinary field users. In this study, we created an internet web-based geographical information system (GIS) interface, which allows users to easily apply APEX after simply drawing a polygon around their field boundary. The interface determines all contributing areas to and through the field drawn, sets up the APEX model simulation, and provides output results to the user for the amount of runoff, sediment loss, nitrogen losses, and phosphorus losses. This impacts field conservation personnel, extension agents, farmers, and others interested in assessing various cropping management system effects combined with environmental and site characteristics on possible pollutant losses.

Technical Abstract: 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.