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

Abstract

Wetland soil properties and stratigraphic heterogeneity influence their water-holding capacity, 15 infiltration, and subsurface flow. Infiltration, however, depends on the soil’s saturated hydraulic 16 conductivity (Ksat) whose spatial variability at field scale is difficult to quantify. In this study, we 17 combined electromagnetic imaging (EMI) and electrical resistivity (ER) with infiltration tests to 18 assess the spatial variation in the shallow subsurface stratigraphy and Ksat at a restored wetland in 19 northwest Ohio. We used a Geonics EM38-MK2, with a transmitter and two receivers spaced 0.5 20 and 1.0 m to map the spatial distribution of the soil’s apparent electrical conductivity (ECa). The 21 ER measurements were acquired along nine transects using a SuperSting R8 resistivity meter 22 with 84-electrode and a dipole-dipole electrode array. The ER results, constrained with 23 lithostratigraphic logs, showed 0.7 m thick topsoil (silty loam) underlain by 0.5 m thick clayey 24 loam interspersed with coarser materials and alternating units of diamictons. The observed ECa 25 were relatively higher (10 – 40 mS/m) for the 0.5 m T-R spacing compared to the 1.0 m spacing 26 (8 – 36 mS/m). The spatial distribution of Ksat ranged from 0.01 – 0.9 mm/min with higher 27 values at areas with high silt and sand content. A least-squared linear regression between Ksat 28 and ECa yielded coefficient of determination (R2) values >0.62 indicating the effectiveness of 29 EMI for predicting the spatial variation of Ksat. Thus, combining geophysical imaging with field 30 infiltration tests provided valuable insights into infiltration through the soil and potential 31 subsurface flow at the restored wetland with limited details on subsurface flow.