Submitted to: International Nitrogen Conference
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 1, 2001
Publication Date: N/A
Interpretive Summary: Tracking subsurface flow of water and chemicals suffers from an inability to locate and evaluate subsurface preferential flow pathways. An approach to locating and evaluating preferential flow that uses ground penetrating RADAR (GPR), near real-time soil moisture sensors, a digital elevation map (DEM), and commonly available geographic information system (GIS) runoff calculation routines was developed. The GPR data and the DEM are used to construct a map of subsurface topography that is then analyzed using GIS routines in the same manner that surface topography is analyzed for runoff. Analysis of patterns from yield maps and remote sensing imagery were used to validate the results. This procedure will be of considerable value to producers and government agencies seeking to understand and control chemical runoff of agricultural landscapes.
Fundamental watershed-scale processes governing chemical flux to neighboring ecosystems are so poorly understood that effective strategies for mitigating chemical contamination cannot be formulated. Adequate characterization of subsurface flow has been especially difficult as conventional sampling methods are ineffective for measuring preferential flow of water and solutes. A sampling strategy using ground penetrating radar mapping of subsurface structures and near-real time soil moisture data, surface topography, remotely sensed imagery and a geographic information system appear to offer a means of accurately identifying subsurface preferential flow pathways. Four small adjacent watersheds draining into a riparian wetland and first order stream at the USDA ARS Beltsville Agricultural Research Center, Beltsville, Maryland are being studied with this protocol. The spatial location of some of the preferential flow pathways for chemicals exiting these agricultural watersheds to the neighboring ecosystems have been identified. Verification of the pathways is via analysis of patterns in yield monitor data and remote sensing imagery.