Effects of soil saturation and pore fluid salinity on complex conductivity

Recent studies have shown that induced polarization (IP) coupled with electrical resistivity surveys can be used for in-situ lithological and hydrologic discrimination of the subsurface; yet the driving factors behind the effects of water content dynamics on IP are relatively understudied. We sought to improve understanding of the relationship of IP on variations in saturation state for an undisturbed agricultural soil. Our experiment consisted of collecting IP measurements concurrently with hydraulic data during multistep outflow experiments. We determined the hydraulic properties of the undisturbed soil samples and correlated them with IP data, primarily changes in saturation. Due to an increase in salinity with decreasing saturation, we found that imaginary conductivity (σ”) may offer distinct advantages for determining moisture content over real conductivity (σ’) measurements. Although σ” exhibits a weaker dependence on saturation compared to σ’, the relative insensitivity of σ” to salinity creates a more robust measure of moisture content in the presence of changing salinities. As changes in pore fluid conductivity are likely to occur in the field simultaneously with water content changes, we argue that, although IP has traditionally been used to discriminate lithology, temporal IP measurements may additionally provide a robust indicator of changes in saturation state.M.S.Includes bibliographical referencesIncludes vitaby David A Gruna