Groundwater-surface water interactions are an emerging area of research. There is a critical need to determine water budgets, to track contaminants moving across the interface (in either direction), and to understand the influence of groundwater discharge on surface water habitats. But obstacles remain to making the necessary measurements. Flux estimates made using mass balance calculations and models do not provide locations of groundwater discharge and recharge. Point measurements made using seepage meters or piezometers and sediment K have been plagued by lack of spatial coverage and reproducibility problems. This research will map the extent and continuity of groundwater recharge and discharge zones at two well-documented sites, Lake Lacawac in Pennsylvania and Mirror Lake in New Hampshire, using a newly-developed marine resistivity system. Measurements collected by towing the electrodes behind the boat on a floating line can be combined with GPS and bathymetry data during data inversion to produce nearly continuous 2-D resistivity profiles. Resistivity responds to variation in porosity, ionic strength of pore fluids, and clay content. In some cases, changes in pore fluid indicate groundwater recharge from the lake (outseepage) or discharge to the lake (seepage). Increase in porosity may indicate likely areas of discharge and increased clay content may indicate areas of restricted groundwater-surface water interaction. Using the resistivity system, measurements can be made over larger areas, and compared with the geology beneath the lake. The geophysical interpretation of potential areas of groundwater seepage or outseepage will tested by deploying an array of low cost manual seepage meters, as well as new logging seepage meters that make use of an electromagnetic flowmeter to detect changes in flow over time. The geophysical surveys will advance knowledge of groundwater-lake interactions by providing better spatial coverage, linkages between geologic features and seepage, and more temporal data in order to examine system response to stresses (both storms and climate change). This research is important to society because of the increasing pressures on freshwater resources. Better understanding groundwater-surface water interactions will improve prediction of water budgets and chemical transfer (i.e., contaminants). Furthermore, seepage interfaces are often hot spots of biological activity and play an important role in nutrient and carbon cycling. This study is designed for transfer to other sites because it looks at the fundamental relationships between the geophysical signal(s) and the observed hydrology. The educational impact of this research occurs at multiple levels. Funds will be provided for three masters students during their second year of study. In addition, undergraduates will act as field assistants and take ownership of research sub-projects. To further enhance their research experience, funding is included to permit undergraduate students to attend a scientific conference and present their research. Temple often attracts first-generation college students and has a 30% minority population; in the geology department, there is a good gender balance among students. Thus, Temple is able to reach under-represented groups in the sciences. In addition to university education, the project will contribute educational materials on the importance of groundwater-lake interaction for tours at the lakes studied.
