Characterization of reactive transport by 3-D electrical resistivity tomography (ERT) under unsaturated conditions

Abstract

The leaching of nitrate from intensively used arable soil is of major concern in many countries. In this study, we show how time lapse electrical resistivity tomography (ERT) can be used to characterize spatially heterogeneous processes of ion production, consumption, and transport in soils. A controlled release fertilizer was introduced into an undisturbed soil core in a laboratory lysimeter and subjected to infiltration events. The production of ions resulting from processes associated with nitrification and their transport through the soil core was observed by time lapse ERT and analysis of seepage water samples from a multicompartment sampler. ERT images show development and propagation of a high‐conductivity plume from the fertilizer source zone. Molar amounts of nitrate produced in and exported from the soil core could be well reproduced by time lapse ERT using a spatial moment analysis. Furthermore, we observed that several shape measures of local breakthrough‐curves (BTCs) of seepage water conductivity and nitrate derived by effluent analyses and BTCs of bulk conductivity derived by ERT are highly correlated, indicating the preservation of spatial differences of the plume breakthrough in the ERT data. Also differences between nitrate breakthrough and a conservative tracer breakthrough can be observed by ERT. However, the estimation of target ion concentrations by ERT is error bound and the smoothing algorithm of the inversion masks spatial conductivity differences. This results in difficulties reproducing spatial differences of ion source functions and variances of travel times. Despite the observed limitations, we conclude that time lapse ERT can be qualitatively and quantitatively informative with respect to processes affecting the fate of nitrate in arable soils.

Spreading of Localized Information across an Entire 3D Electrical Resistivity Volume via Constrained EMI Inversion Based on a Realistic Prior Distribution

“…As such, they are useful to infer the electrical resistivity (and chargeability) of the subsurface [1][2][3][4]. ERT data are collected using arrays of dozens of electrodes coupled with the soil to ensure galvanic contact with the ground and are, nowadays, regularly inverted using 2D or 3D forward modeling [5][6][7]. On the contrary, EMI measurements can be performed without any physical contact with the surface and can be generally inverted using simple 1D forward modeling [8][9][10].…”

Real-Time Monitoring and Simultaneous Verification of Water Percolation Using Electrical Resistivity Tomography and Photography Techniques

“…To solve these limitations, geophysical exploration methods, such as ERT [7][8][9][10][11][12][13] and ground-penetrating radar [14][15][16][17], are commonly employed. These methods have a minimal impact on the soil and allow for profile measurements.…”