Ecohydrogeophysics at the Edwards Aquifer: insights from polarimetric ground-penetrating radar
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Three-dimensional multicomponent ground-penetrating radar (GPR) reflection data and horizontal GPR transmission profiles were acquired and analyzed to better understand the interaction of vegetation with subsurface flow conduits at a hydrologic experimentation site. Previous researchers conducted a set of shallow (<2.5 m) subsurface hydrology experiments during simulated rainfall events within a small plot (7 m x 14 m) on the fractured and karsted limestone of the Edwards Aquifer region near San Antonio, Texas, USA, to better understand the influence of Juniperus ashei brush control on the local hydrology. Tracer experiments showed a high degree of variability in tracer recovery, advection speed and concentration depending on the location of the application of the tracer. Both 3D multicomponent GPR reflection images and coherency and inversion of GPR horizontal transmission profiles were utilized to identify the main conduits of flow within the experimentation site in order to explain the observations of the experiments. The 3D multicomponent GPR and coherency images revealed that the most obvious potential conduits run nearly parallel with the observation trench. Inversions of the horizontal transmission profiles indicate that some conduits are filled with soil while others have no fill. This information helps explain the high spatiotemporal variability observed in the tracer data. Additionally, the GPR and hydrologic experiments suggest that Juniperus ashei significantly impacts infiltration by redirecting flow towards its roots occupying fractures within the rock. This study demonstrates that GPR provides a noninvasive tool that can improve future subsurface ecohydrologic experimentation. 2009 European Association of Geoscientists & Engineers.