The Sand Hills aquifer system hosts hundreds of shallow lakes having salinity levels ranging from fresh water to more than 100 g/L. To date, the mechanisms responsible for generating and maintaining these large salinity gradients are poorly understood. In this study, we plan to determine whether or not the spatial and temporal variations in lake salinities observed across the Sand Hills aquifer system are due to: 1) differences in the ratio of groundwater inflow/outflow to lake evaporation or 2) spatial variations in delivery of solutes to lakes from local- and regional-scale groundwater flow systems. In order to test these different end-member hypotheses of lake salinization, we will develop detailed three-dimensional models of variable-density groundwater flow, solute transport, and surface water-groundwater interactions for our study area. The models will be tested using new geophysical (EM, MR, TDEM) surveys. We will also collect hydraulic, geochemical, and isotopic samples of lake water and groundwater in order to characterize the surface/subsurface solute distribution in the near-lake aquifer zone. We will evaluate temporal trends in lake salinity using diatoms and optically-stimulated luminescence methods. The study will lead to improved subsurface salinity detection methods and a better understanding of the consequences of deposition of large volumes of dense saline fluids over shallow freshwater aquifers that result from large-scale environmental disasters, such as tsunamis (e.g., Indonesia, Bangladesh in 2005) and hurricanes (e.g., Mississippi and Louisiana, U.S., 2005). These physically based models may also be applicable to dune-lake systems in other regions, where dune lake systems play an important role in local hydrology and water resources (e.g., China, Niger, Australia). The project will support a number of undergraduate and graduate students from the University of Nebraska, Indiana University, and Oklahoma State University. In addition, we will directly involve K-12 students and teachers in Western Nebraska where the density of population is below 1 person per square km. The study will bring together hydrologists, geophysicists, and limnologists from Australia and North America.
