Time-domain reflectometry (TDR) is a geophysical tool used in the field and laboratory to determine soil moisture, bulk soil electric conductivity (EC). We employ this tool in many ways to understand temporal and spatial soil dynamics in a small catchment. Several hundred sites within this catchment, located in the Valles Caldera National Preserve, were surveyed using TDR with the intention of characterizing the spatial distribution of soil properties. Data was collected a few weeks after the snowmelt, when we assumed the soil to be at field capacity and therefore, the relationship between soil texture and moisture content is strongest. Laser diffraction particle size analyses of the soils sampled in this survey demonstrated that bulk soil EC correlates very strongly to clay and sand fractions. This relationship provides us with an estimate of soil texture once the difference between estimated clay and sand is calculated. A pedo-transfer function, Rosetta, is used to approximate saturated hydraulic conductivity, Ksat. In order to test the effectiveness of estimating Ksat using this method, ring infiltrometers were used at numerous sample locations. To further investigate the relationship between bulk soil EC and clay, the same type of survey in two catchments of different parent material was completed earlier this year Temporal characterization is achieved with the use of data from soil pits instrumented at several depths with sensors recording, water content, EC, temperature, and matric potential at 10 minute intervals. Preliminary results from HYDRUS 1-D will guide us in determining whether or not a 2 or 3-D model is necessary to characterize subsurface dynamics.
Jones, C.A., Schaap, M.G. (2011): TDR-EC: A Rapid Subsurface Characterization of Particle Size & Hydrologic Properties. AGU Fall Meeting Presentations (Poster) Abstract H41D-1052..