This grant supports acquisition of an ten channel electrical resistivity (ER) system (IRIS Syscal Pro) for the Department of Geosciences at Penn State University. ER is sensitive to changes in the electrical conductivity of the shallow subsurface and has applications for spatially and temporally resolved observations of subsurface fluid content and composition. As measured resistances between source and receiver electrodes record the average electrical properties of porous media and conductive fluids along the path length, measurements are a useful complement to discrete in situ sampling and observations from wells. The ER system will support a range of research including remote time series monitoring of hydrologic tracer transport, imaging solute transport between aquifers and stream base flow, studies of groundwater transport in desert ecosystems, and studies of the kinetics of subsurface diagenesis of organics via bacterial iron reduction. The ER system will support research at a Critical Zone Observatory (Shale Hills) and research training through a three-week integrated hydrogeophysics summer course aimed at underrepresented undergraduates from three Historically Black Colleges and Universities partnered with Penn State (Jackson State University, MS; Fort Valley State University, GA; and Elizabeth City State University, NC).
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The resistivity meter purchased with this grant allows us to "see" into the Earth, similar to a medical CAT scan; however, as geophysicists, we’re forced to work with partial views rather than what is available to doctors, reconstructing what’s below the land surface from slices that might not tell the whole story. Because we only get partial information, these indirect data are considered in conjunction with other direct sampling measurements. Because taking direct measurements of many of these properties is often too expensive to be feasible, geophysicists use these indirect, inexpensive methods to help guide the location of sampling and to interpolate between them. We have used this instrument to explore a number of subsurface processes where we otherwise wouldn’t have data: to help determine the movement of contaminants in groundwater, changes in moisture content in soils after fire, the extent of permafrost thaw, and also the movement of sap in trees. These data have been collected at a range of research sites across the country, including some long-term research sites such as Peru Creek, near Keystone, Colorado, and the Boulder Creek Critical Zone Observatory. The equipment has also been used in lab studies, by a field methods course taught at the Colorado School of Mines, and also by approximately 10 graduate students in their research.
