Assessing subsurface heterogeneity and infiltration capacity at a restored wetland using geophysical imaging and infiltration tests

Wetland soil properties and stratigraphic heterogeneity influence their water-holding capacity, infiltration, and subsurface flow. Infiltration, however, depends on the soil’s saturated hydraulic conductivity (K _sat ) whose spatial variability at field scale is difficult to quantify. In this study, we combined electromagnetic imaging (EMI) and electrical resistivity (ER) with infiltration tests to assess the spatial variation in the shallow subsurface stratigraphy and K _sat at a restored wetland in northwest Ohio. We used a Geonics EM38-MK2, with a transmitter and two receivers spaced 0.5 and 1.0 m to map the spatial distribution of the soil’s apparent electrical conductivity (ECa). The ER measurements were acquired along nine transects using a SuperSting R8 resistivity meter with 84-electrode and a dipole-dipole electrode array. The ER results, constrained with lithostratigraphic logs, showed 0.7 m thick topsoil (silty loam) underlain by 0.5 m thick clayey loam interspersed with coarser materials and alternating units of diamictons. The observed ECa were relatively higher (10–40 mS/m) for the 0.5 m T-R spacing compared to the 1.0 m spacing (8–36 mS/m). The spatial distribution of K _sat ranged from 0.01–0.9 mm/min with higher values at areas with high silt and sand content. A least-squared linear regression between Ksat and ECa yielded coefficient of determination (R ² ) values > 0.62 indicating the effectiveness of EMI for predicting the spatial variation of K _sat . Thus, combining geophysical imaging with field infiltration tests provided valuable insights into infiltration through the soil and potential subsurface flow at the restored wetland with limited details on subsurface flow.