SECO CREEK WATER QUALITY DEMONSTRATION PROJECT IMPROVES WATER QUANTITY AND WATER QUALITY ASSOCIATED WITH THE EDWARDS AQUIFER

The Edwards Aquifer provides water for over 1.3 million Texans and 103,000 acres of irrigated land. It is the sole-source aquifer providing municipal, industrial, and recreational water for San Antonio and other cities and communities overlying the aquifer. Edwards Aquifer is excellent quality when compared to United States Environmental Protection Agency (USEPA) drinking water standards.

Karst topography overlies the aquifer and during high intensity rainstorms sediment and other contaminants move directly into the aquifer through fractured limestone, sinkholes, and open caves, and could eventually threaten the health of the aquifer. One of the primary goals of the Seco Creek Water Quality Demonstration Project which covers approximately 170,000 acres, mostly rangeland, is to prevent contamination and to increase the awareness of producers, landowners, and the public concerning the hazards of non-point pollution.

As a result of project activities, numerous producers and landowners have realized environmentally safe agricultural practices exist that continue to provide economical benefit. Precision herbicide application techniques and prescribed burning on rangeland are two practices that have had impact on the watershed and have contributed toward the prevention of non-point source contamination. Another demonstration is showing that short grazing periods followed by adequate rest to allow re-growth have the potential for improving surface water quality, infiltration, and reducing the detrimental effects of drought on the vegetation.

United States Geological Survey (USGS) has noted an improvement in water quality at spring enhancement sites including a decrease in total ions as well as nitrates. The following table shows the baseline and post treatment water quality at four spring enhancement sites:

Water quality at spring enhancement sites - baseline conditions in ppm

Water quality spring enhancement sites - post treatment conditions in ppm

Best Management Practices (BMP) applied during the demonstration project have led to the reduction in the addition of agricultural chemicals. In one 8000 acre block of cropland, annual nitrogen applications were reduced an estimated 20 percent and phosphorus the same amount. An integrated brush management program on rangeland has made it possible to use all available technology for managing undesirable vegetation. The use of the herbicides, Triclopyr and picloram, have been reduced forty percent by simply modifying application techniques. Where prescribed burning has been substituted for chemical control, herbicide use has been completely eliminated. These practices, along with improved irrigation water management on cropland have significantly reduced chemical loading at the bottom of the root zone.

Recent evaluations by the USGS and others of the Edwards Aquifer show no identified water problems. However, increasing demands on the aquifer as a water supply coupled with uncertain precipitation does point to future water quantity problems. Two separate demonstrations in the Seco Creek project point to water quantity increases to the Edwards Aquifer through selective woody plant management that increases water yield from rangeland watersheds. The two demonstrations show an increase of 35,000 to 55,000 gallons of water per acre per year following the selective removal of certain woody species. The implementation of species management across the entire Edwards Plateau region of Texas could have tremendous positive impact on both water quality and quantity in the Edwards Aquifer.