Aquatic electrical resistivity imaging of shallow-water wetlands

Abstract

This study uses aquatic electrical resistivity imaging (ERI) to predict spatial and temporal patterns of pore-fluid conductivity in wetland soils of a shallow-water wetland. The technique involves floating electrodes from a paddleboat. Resistivity measurements for the study were obtained six times over a four-month period, covering a [Formula: see text] grid. Three-dimensional inversion is used in the study to determine the conductivity distribution of the subsurface, using the smoothness-constrained least-squares optimization method. Surface water depth and conductivity were entered as known information in the 3D inversion and measurement error (for constraining the inversion) estimated from tie points. Pore-fluid conductivity was constrained using (1) surface conduction measurements obtained from laboratory experiments on soils extracted from the wetland and (2) a correction for temporal and spatial temperature variations using direct surface water temperature measurements. The study demonstrates that aquatic ERI is an ideal method for determining the resistivity structure of wetland sediments covered by a shallow surface water layer. In the field example presented here, changes in pore-water conductivity estimated from inverted models suggest that contamination migrates from marginal landfills into the wetland soils during rainfall.