RAPID SITE CHARACTERIZATION OF OHIO RESTORED WETLANDS USING GEOPHYSICS

Restored wetlands (RWs) are a popular treatment solution for Lake eutrophication globally and in the United States. Researchers and managers must therefore monitor RW nutrient retention to quantify wetland health and effectiveness. Nutrient retention in wetlands, however, depends on hydrological and biogeochemical properties and processes within their soils, which vary spatially and temporally. Conventionally, quantifying soil nutrients is done by collecting intact cores at random or chosen points at a site. RWs have highly heterogeneous soil, thus, point sampling of intact cores is not an efficient means of characterization. Using soil stratigraphy to understand preferential water flow paths is another means to track nutrients. Non-geophysical methods for characterizing stratigraphy require boreholes that compromise soil structure and may not yield high-resolution results. Geophysical methods provide a cost-effective and minimally invasive alternative to investigating subsurface information at a high spatial scale. This study combines geophysical methods including electromagnetic induction (EMI), ground penetrating radar (GPR), and electrical resistivity tomography (ERT) with soil properties and stratigraphic units, to provide a better understanding of spatial soil variability in RWs. GPR, EMI, and ERT datasets collected at three wetland sites in northwest Ohio were correlated with bulk density, soil organic matter, and porosity. Point samples were collected and analyzed in a separate laboratory to ground-truth geophysical measurements. Results show that porosity, soil organic matter, and bulk conductivity correlate strongly with EMI. GPR was shown to be an effective means of determining soil stratigraphy between 0 and 4m. ERT was able to identify potential aquifers and stratigraphic units up to approximately 20m. These results indicate that geophysical methods are an effective means of rapid site characterization for complex wetland systems.