Telesford-Checkley, Judlyn Merium (2014-12). Assessing Avian Contribution of Escherichia coli and Nutrient Loads to Watersheds. Doctoral Dissertation.
The impairment of waterways by pathogens as indicated by the detection of high Escherichia coli (E. coli) levels continues to be a problem in Texas. Almost half of the assessed waterbodies designated for contact recreation in Texas are impaired by bacteria. In addition, Texas is in the process of developing nutrient criteria for waterbodies. Avian species such as herons and egrets frequently establish large heronries in close proximity to water. These heronries are potentially major contributors of nutrients and E. coli to watersheds. I enumerated E. coli in water and fecal samples from four heronries dominated by cattle egrets (Bubulcus ibis) during 2011, 2012, and 2013. I compared the fecal sterol profiles of feces to those of water associated with each heronry using sterol ratios, correlation analyses, and principal component analysis. I also analyzed total nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sodium (Na), sulfur (S), zinc (Zn), copper (Cu), iron (Fe), manganese (Mn), and boron (B) in water and fecal samples and compared concentrations among sample types. I found that E. coli and nutrients deposited through feces from birds at heronries are influenced by the size and location of the heronry. The highest E. coli counts in water samples were collected at the two larger heronries, which were both located directly over water. In addition, the highest estimated E. coli loads generated by adults ranged between 2 x 1014 and 4 x 1014 Colony Forming Units (CFU) breeding season^-1. I also found positive correlations between E. coli counts and the sum of bird sterols from water direct under a heronry. N and P concentrations in water samples were as high as 62.4 mg/L and 4.69 mg/L, respectively. K, Ca, Mg, and Fe were most abundant in feces and/or water samples and when birds nested directly over water, concentrations of K, Ca, and Mg were significantly higher than concentrations in water adjacent to birds nesting on islands. The results obtained in this study contribute to furthering the understanding of the potential contributions of bacteria and nutrients from large heronries located on the edge of or near waterbodies.