Field and laboratory Validation of ERT-Detected Subsurface Heterogeneity at the Meter Scale

Abstract

Agriculture, industry, airport activities all have impact on the quality of soil and water. To improve risk assessment, monitoring, design and implementation of cost-effective preventive or mitigation measures and/or policies we require a better understanding of the underlying environmental processes. Spatial heterogeneity plays a critical role for describing water and solute transport processes in the unsaturated zone. Heterogeneous water flow in soils is complex and challenging to quantify due to changes in soil hydraulic properties across different spatial scales. We conducted an experiment involving different field and laboratory sensory techniques and measurements to examine 3D functional heterogeneity and its physical drivers in natural soil. We compare the spatial heterogeneity of the soil from ERT measurements at two scales with the observed spatial distribution of hydraulic properties calculated from soil samples and TDR data. ERT helped to visualize the heterogeneity of the studied system. Although at first the high resistive feature observed with ERT could not be explained by tensiometer and/or TDR data, there was a distinct difference in the retention curves inside and outside the feature, which creates difference in resistivity values. These observations help us to better understand the links between soil hydraulic properties and heterogeneous water flow.