INVESTIGATION OF WATER QUALITY AND GROUNDWATER FLOW IN A KARST WATERSHED IN BLANCO COUNTY, TEXAS

Water sampling and flow measurements were conducted to advance the understanding of a complex karst system by integrating studies of water quality and water quantity around the Honeycut Creek Spring, Blanco County, Texas. Spring responses to rainfall have been investigated by hydrochemical and isotopic analysis as tracers. These investigations would create a baseline model for a better understanding of how the aquifer responds to recharge events.

Flow measurements revealed that the discharge of Honeycut Creek Spring does not respond to local and regional precipitation. The wettest September in 2018 in recorded history in south-central Texas resulted in minimum discharge, which is one order of magnitude lower than the discharge recorded from April 2017. During low flow conditions, the salinity of spring water is higher with elevated levels of nitrate and higher concentrations of other ions, especially sulphate. The δ¹⁸O and δD measurements of Honeycut Creek Spring water samples were performed on a Picarro L2130-i water isotope analyzer (cavity ring-down spectroscopy, CRDS) in the Department of Geological Sciences, University of Texas at San Antonio. There are little variations for the water isotopes of Honeycut Creek Spring during 2017-2018, which may demonstrate relatively long residence time of groundwater and a deeper flow path. This could also explain why the discharge of Honeycut Creek Spring does not respond to local and regional precipitation. The deuterium excess values of these spring water samples are close to 10%, which may indicate little evaporation during precipitation infiltration and groundwater movement.