Comparison of Heterogeneous Transport Processes Observed with Electrical Resistivity Tomography in Two Soils

Preferential flow in soils can manifest itself in several ways. To illustrate this, we analyzed solute transport during a step tracer experiment in two soils expected to differ in their governing transport processes: a loamy sand and a silty soil. By combining electrical resistivity tomography (ERT), time domain reflectometry, and effluent measurements, we observed different preferential flow phenomena. The transport process was characterized using voxel- and column-scale effective convective-dispersive equation (CDE) parameters, local velocities, and leaching surfaces. At the column scale, transport in the loamy sand was dominated by a homogenous convective-dispersive transport behavior, but at the scale of the voxel, preferential transport was observed. Transport in the silty soil was considerably more heterogeneous. Preferential flow was identified using ERT, voxel- and column-scale effective CDE parameters, local velocities, and leaching surfaces. In these soils, a clear influence of soil layering on solute transport was observed.