Soil structure and soil moisture dynamics inferred from time-lapse electrical resistivity tomography

The semi-arid sagebrush steppe in the western United States faces pressures from agriculture industry, recreation use, invasive grasses, and a changing climate. A key to facilitating healthy management of this ecosystem is understanding distribution behavior soil moisture vadose zone both natural agricultural settings. Within unsaturated environments, spatially temporally heterogeneous, changes porosity permeability within arid soils complicate characterization hydrologic properties. Importantly, accumulations ‘caliche’ or pedogenic calcium carbonate can greatly limit permeability; however, observing role that caliche plays process difficult because installation situ instruments disturbs only provides information at single point. To investigate processes on broad temporal spatial scale, we installed 7x8m2 electrical resistivity tomography (ERT) array Reynolds Creek Critical Zone Observatory southwestern Idaho. Existing observations show infiltration limited depths less than 60 cm site, as compared least 90 other sites watershed. capture seasonal wetting drying soils, well soils’ response rainfall events, monitored site bi-weekly during spring, summer, fall 2015 2016. time-lapse ERT was placed adjacent coaxial impedance dielectric reflectometry (CIDR) probes so data could be referenced precise measurements volumetric water content. In addition provided by CIDR probes, texture analysis profile descriptions near-by pit typical morphology, with clays B horizon. resulting inversions following structure: (1) high-resistivity top layer corresponding minor amounts carbonate; (2) low-resistivity intermediate substantial (stage IV) (3) deep saprolite. varies seasonally precipitation, while does not. This agrees depth measured suggests limits infiltration. However vertical structure cracks create preferential flow paths; these paths responds large precipitation events moisture. implies are conduit for not captured probes. From combined interpretation conclude presence calcic horizons inhibits summer dry months winter wet flux period; provide an important connection between shallow portions critical zone.