Bacterial loadings watershed model in Copano Bay



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Copano Bay currently exceeds fecal coliform Texas Surface Water Quality Standards for oyster water use. Aransas and Mission River Tidals currently exceed enterococci water quality standards for contact recreation use. The fecal coliform Copano Bay Bacterial Loadings Model will be used to support the TCEQ Total Maximum Daily Load (TMDL) program to develop the TMDLs for the three impaired water segments. The objectives of this research are to identify the major bacterial sources in the Copano Bay watershed, to calculate the total bacterial loadings (i.e., the TMDLs) from these sources, and to estimate the load reductions needed to bring each of the impaired segments into compliance with water quality standards. The potential bacterial sources that were considered in the model were wastewater treatment plants (WWTPs), waterbirds, livestock, failing septic systems, and other non-point sources that originate from different types of land uses (e.g., urban, forest, etc.). This thesis presents an analysis of the existing bacterial monitoring dataset for fecal coliform, including spatial and statistical analysis of the bacterial monitoring data, an estimation of fecal coliform loadings (the input into the models), including non-point and point source calculations, and a description of bacterial transport of fecal coliform from the sources in the watersheds, rivers, and Copano Bay using the model, including explanations for how the model parameters were determined. The main assumptions used in the model were that the fecal coliform bacteria decay (first-order reaction rate) in watersheds and along streams and channels, and Copano Bay is divided up into four Continuous Flow, Stirred Tank Reactors (CFSTRs). The results of the research include the modeled median fecal coliform concentrations throughout the watershed, the impact of different bacterial sources on each of the water segments in Copano Bay watershed, and the load reductions needed (and from what sources) to meet fecal coliform water quality standards. Cattle were determined (based on model results) to be the largest fecal coliform contributor of fecal coliform in Copano Bay.