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Title:   Author  item
                                            Walthall, Charlesitem
                                            Gish, Timothyitem
                                            Daughtry, Craigitem
                                            Dulaney, Wayneitem
                                            KUNG, K-J - UNIV. WISCONSINitem
                                            McCarty, Gregoryitem
                                            Timlin, Dennisitem
                                            Angier, Jonathanitem
                                            SENTEK, P. - AUSTRALIAitem
                                            HOUSER, P. - NASA
  Submitted to: International Nitrogen Conference
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 10/1/2001
                                    Publication  Date: N/A
                                    Citation: N/AInterpretive 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.
                                Technical Abstract: 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.


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