GEOELECTRIC EVIDENCE OF REGIONAL CONTROLS FOR GROUND WATER DISCHARGE FROM SALINE LAKES

Ground water-dominated saline lakes in eolian semi-arid environments are direct manifestations of climate change resulting from a shift from dry to wet conditions. An antecedent arid climate creates conditions for dune development, while the following wet period results in the water table rising creating lakes in interdunal valleys. The salinity of these lakes range three orders of magnitude from fresh to brine, while upgradient ground water is fresh. A consensus exists that the elevated salinity results from ground water and lake evaporation in the Sand Hills of Nebraska. Solute advection, diffusion, dispersion, variable-density flow in ground water, and eolian transport of dust forms of salts are processes that control salinization and divergence of salinity paths between different lakes. It is now feasible to simulate the influence of variable-density groundwater near lakes, in addition to the topography-driven flow that completely dominated lake studies previously, but field data to support the models are lacking. Using two dimensional electrical resistivity imaging of three lakes on the kilometer-scale in the Sand Hills, the location of saline discharge from the lakes was mapped. The results to date indicate that geological and regional hydrogeological controls exert greater influence on the saline plumes discharging from the lakes than local topography. The lakes appear to be poorly connected in the subsurface and generate independent plumes of saline water. Additional work will be performed using borings to confirm the geoelectrical evidence of plume location.