ARBOREAL UPTAKE, DROUGHT AND INTERNAL SEDIMENT BUILDUP AS POSSIBLE CAUSES FOR DISCHARGE RATE VARIATION IN THE EPIKARST AND MANTLED KARST AQUIFER AT SAVOY EXPERIMENTAL WATERSHED

A comparative study of variable discharge rates in six epikarst springs and two overflow-underflow base-level springs at Savoy Experimental Watershed (SEW) reflects the spatial and temporal variation of the groundwater flow system in a mantled karst aquifer.

SEW is a site for long-term collaborative research on hydrology and animal waste management owned by the University of Arkansas and located in the Southern Ozarks. It encompasses 1250 hectares which have been delineated into six watershed basins. Past studies at this site have focused on conduit flow and transport in the nearly flat-lying, mid-Paleozoic, regolith-mantled karst, comprised of the Boone and St. Joe limestone Formations which overlie a regional confining unit, the Chattanooga Shale Formation.

This specific study is part of a long-term assessment of hydrologic budget components in Basin One at SEW. It is conducted as part of the Research Experiences for Undergraduates (REU) program and is funded by the National Science Foundation. Within Basin One there are six small springs that contribute to a losing stream which seeps back into the aquifer and is discharged through two larger springs further downgradient. Spatial and temporal variance in discharge rates at these seeps is believed to be a product of three possible causes: uptake by trees, recent climatic variation and sediment accumulation within the aquifer. Discharge rates, conductivity, temperature and pH level for three of the springs from two three week periods in July and December of 2005 are compared with similar data for the same three springs for the month of July, 2006. All three demonstrate significantly decreased discharge rates during extreme low-flow conditions. The five other springs likewise appear to have notably decreased discharge rates. In order to discern the primary causes for the reduction in discharge from these springs multiple tracer testing will be used to provide rigorous assessment of new developments in the hydrologic budget at this location.