GEOCHEMICAL SPATIAL VARIABILITY OF THE COLORADO RIVER ASSOCIATED WITH KARST SPRINGS, COLORADO BEND STATE PARK, CENTRAL TEXAS

Numerous karst springs discharge from Ordovician Ellenberger carbonates along the Colorado River in Colorado Bend State Park at the boundary between San Saba and Lampasas Counties in Central Texas. Seven perennial springs have traditionally been recognized within the park along an eight kilometer stretch of the Colorado River, but more are suspected to discharge below stream level as the deeply incised Colorado River functions as a major regional potentiometric low. In order to attempt to delineate additional springs in the study area, a YSI Multi-parameter Sonde coupled with a GPS was used to map geochemical variability within the Colorado River. The Sonde was towed with kayaks through two traverses of the eight kilometer river stretch, continuously recording parameters that include: conductivity, dissolved oxygen, pH, resistivity, salinity, temperature, total dissolved solids and turbidity. Collected data was plotted through spatial interpolation using geographic information system software (ArcGIS). Comparison of spatial variability of river chemistry suggests that several additional springs discharge subaqeously through fractures or conduits into the Colorado River within the study area; however, the dominance of input from known perennial springs masks much of the signature of suspected smaller springs. Additional sampling is planned to unequivocally delineate exact spring discharge locations in order to develop better models of the complex karst hydrogeology within this Ellenberger karst system. This study shows the potential for spring inventories using multi-parameter sondes in other karst regions where additional springs are suspected to contribute to fluvial systems.