According to the USEPA National Section 303(d) List Fact Sheet, bacterial pathogens are the leading cause of water quality impairments in Texas. The automated Spatially Explicit Load Enrichment Calculation Tool (SELECT) uses spatially variable factors such as land use, soil condition, and distance to streams to characterize pathogen sources across a watershed. The results support development of Total Maximum Daily Loads (TMDLs) where bacterial contamination is of concern. SELECT calculates potential E. coli loads by distributing the contributing source populations across suitable habitats, applying a fecal production rate, and then aggregating the potential load to the subwatersheds. SELECT provides a Graphical User Interface (GUI), developed in Visual Basic for Applications (VBA) within ArcGIS 9.X, where project parameters can be adjusted for various pollutant loading scenarios. A new approach for characterizing E. coli loads resulting from on-site wastewater treatment systems (OWTSs) was incorporated into the SELECT methodology. The pollutant connectivity factor (PCF) module was created to identify areas potentially contributing E. coli loads to waterbodies during runoff events by weighting the influence of potential loading, runoff potential, and travel distance. Simulation results indicate livestock and wildlife are potentially contributing large amounts of E. coli in the Lake Granbury Watershed in areas where these contributing sources are not currently monitored for E. coli. The bacterial water quality violations near Lake Granbury are most likely the result of malfunctioning OWTSs and pet waste in the runoff. The automated SELECT was verified by characterizing the potential E. coli loading in the Plum Creek Watershed and comparing to results from a prior study (Teague, 2007). The E. coli potential load for the watershed was lower than the previous study due to major differences in assumptions. Comparing the average ranked PCF estimated by physical properties of the watershed with the statistical clustering of watershed characteristics provided similar groupings. SELECT supports the need to evaluate each contributing source separately to effectively allocate site specific best management practices (BMPs). This approach can be used as a screening step for determining areas where detailed investigation is merited. SELECT in conjunction with PCF and clustering analysis can assist decision makers develop Watershed Protection Plans (WPPs) and determine TMDLs.

A scarcity of comparable research on the transport of bacteria has forced hydrologic models to assume that bacteria travel as dissolved chemicals. In reality, most bacteria preferentially attach to soil aggregates, and behave very differently from planktonic bacteria. The goal of this research project was to identify and evaluate a laboratory method for partitioning between attached and planktonic bacteria that could be used to improve hydrologic modeling. Attachment was measured indirectly as the difference between total and planktonic bacterial concentration. Planktonic concentration was defined as the concentration of bacteria that could pass through an 8 μm screen. Total concentration was determined by disaggregating attached bacteria through a dispersion treatment. A randomized complete block design was structured to test for the effects of filtering, two dispersion treatment options, and the presence of soil on concentration. Tween-85 surfactant was selected as the best dispersant for use in further studies. About 78% of bovine <I>E. coli</I> in the laboratory samples were adsorbed/associated with sterile soil particles. Twenty samples of different bacteria-soil ratios were analyzed using this method to develop an isotherm equation describing <I>E. coli</I> partitioning. The <I>E. coli</I> used to inoculate these samples was cultured using a chemostat reactor to control cell growth stage and control variability. A linear isotherm (R²=0.88) was selected to describe this experimental data; however, future studies characterizing the partitioning behavior of <I>E. coli</I> under different environmental conditions are recommended in order to better understand attachment prior to modeling attached and planktonic <I>E. coli</I> separately. / Master of Science

The median total dissolved phosphorus concentration (0.41 mg/L P) of groundwater from the Mississippi River Valley alluvial aquifer exceeded the U.S. Environmental Protection Agency’s stream nutrient criteria (of 0.1 mg/L P) and the national background for phosphorus in groundwater (0.02 mg/L P). A general association between elevated phosphorus and dissolved iron concentrations suggests that reducing conditions that mobilize iron in the aquifer also may facilitate transport of phosphorus. These elevated concentrations of phosphorus may indicate phosphorus in the study area may be concentrated through irrigation return flow and groundwater discharge, and may contribute to the Gulf of Mexico hypoxic zone. The data do not appear to follow any spatial, geologic, or application pattern. The research indicates that phosphorus concentration in the aquifer was primarily sourced from natural geochemical reactions within the aquifer media.

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