WATER TEMPERATURE AS AN INDICATOR OF SURFACE WATER-GROUND WATER INTERACTIONS IN A KARST HYDROGEOLOGIC SETTING

The degree to which surface water interacts with the underlying ground water system is important for hydrologic modeling, wellhead protection, bank filtration, conjunctive use, stream ecology, and non-point source pollution concerns from adjacent lands. Streams, lakes, and wetlands in carbonate settings exhibit a wide variety of relationships with respect to the underlying ground water system. Water temperature data provide both qualitative and quantitative information on the nature of the surface water-ground water interactions. In the hydrogeological setting of the karst-underdrained, Nittany Valley in the Valley and Ridge Province of the Appalachian region of central Pennsylvania, two field studies were conducted from 1998-2002 to evaluate the interactions between surface water bodies and the underlying ground water systems. Time series of surface and ground water temperature were used to determine seasonal variations of surface water-ground water interactions in streams and wetlands. In the stream study, surface and ground water temperatures were recorded at hourly intervals during the period of stream flow along a losing stream segment during 2002. Regression analyses of air temperature versus surface water temperature revealed that the stream reverted from losing to gaining conditions for a two-month period of above normal precipitation. Total precipitation for the months of May and June (36.1 cm) was approximately five times larger than the long-term average. The deviation from predicted surface water temperatures was found to relate well to measured ground water inputs, indicating that time series of surface water temperature data can provide information on seasonally varying ground water inputs. In a nearby chain of 17 karst wetlands located adjacent to one of Penn State University’s wastewater irrigation sites, surface water and ground water temperatures were recorded on a monthly basis during 1998-1999 in ponds and piezometer nests screened at four depths from 1.5 to 9.1 meters. Ground water temperatures compared to surface water temperatures indicated the perched nature of the ponds and complimented hydraulic head data. These studies indicate that water temperature data provide a low-cost tool to analyze spatial and temporal variations of surface water-ground water interactions.