Monitoring nonpoint source pollutants in the vadose zone with GIS

Nonpoint source (NPS) pollutants are recognized as the single greatest threat to surface and subsurface sources of drinking water throughout the world. The vadose zone serves as the conduit through which NPS pollutants travel through surface soil to groundwater supplies. Because of increased dependency on groundwater supplies, the ability to model groundwater vulnerability to the leaching of NPS pollutants through the vadose zone has grown in significance. Geographic information systems (GIS) have emerged as a useful tool in environmental modeling, particularly for NPS pollutants. A review is presented concerning the modeling of NPS pollutants in the vadose zone with GIS. Areas discussed include the significance of NPS pollutants as a global environmental problem, the justification for the modeling of NPS pollutants in the vadose zone with GIS, the basic components of environmental modeling with GIS, a review of existing GIS-based NPS pollutant models, the application of geostatistics to GIS-based NPS pollutant modeling, the influence of scale, the reliability of NPS pollutant models based on model error and data uncertainties, and the future direction of GIS-based NPS pollutant modeling. The proliferation of GIS-based NPS pollutant models holds promise, yet caution is needed to avoid misuse of a potentially valuable environmental assessment tool for decision makers.