A field-based evaluation of the effects of spatial and temporal variability on water quality along Geronimo Creek watershed in Guadalupe County, Texas

With the exploding human population coupled with the advancements in technology and sophistication in life style, water quality is constantly being compromised and has lately been getting the desired attention from all the stakeholders. Following the monitoring results on Geronimo creek by Guadalupe-Blanco River Authority (GBRA) as reported in the 2004 and subsequent Texas Water Quality Inventory (TWQI) and the Federal Clean Water Act (CWA) 303(d) List, bacteria concentrations exceeded the standard for normal recreational use (mean of 162 organisms/100 mL) while the nitrate-nitrogen level was documented as high and increasing (mean concentration of 11.0 mg/L). This study monitored water quality for twelve months along the Geronimo Creek in Guadalupe County, Texas in order to conduct an assessment of pollutants, their estimates and likely sources. It also examined the influence of spatial and temporal variability on the water quality along the entire segment of Geronimo creek. The study goal was to conduct and present a Texas Commission on Environmental Quality Clean Rivers Program (TCEQCRP) quality assurance-compliant water quality monitoring and data analysis to establish an estimate, likely origin and distribution of pollutants for various planning and management needs. Statistically, monitoring data was analyzed using the two-way ANOVA to assess the impact or contribution of land use and/or season on water quality of Geronimo creek during the sampling period. Correlation analysis was also done on some of the parameters. Data was compared with established state standards to determine compliance. Consistent with the foregoing, this study focused on sampling flow, field, conventional, and bacteriological parameters to establish baseline pollutant levels for future monitoring programs. The majority of the routine water quality parameters were at levels lower than what would be considered detrimental to the stream and public health. Only TSS, total hardness, E. coli and nitrate-nitrogen values exceeded specific limits established by state agency. Metal toxicity was not an issue with this creek as the metal concentrations of both historical and current monitoring programs were far below the established standards. The Soil and Water Assessment Tool (SWAT) was applied to quantify, and predict under different control scenarios, the effects of the reported impairments and guide the development of best management practices (BMPs) for reducing the nitrate and E. coli levels. It was, however, verified that the model could not produce reliable results given the available data and location of existing stream flow monitoring station. Necessary recommendations for a reliable future data collection and better modeling results were identified.