Instream Bacteria Influences from Bird Habitation of Bridges

The representativeness of ambient water samples collected from bridge crossings has occasionally been challenged because critics contend birds nesting on bridges elevate fecal indicator bacteria concentrations over samples collected from river reaches not spanned by bridges. This study was designed to evaluate the influence, if any, of bridge‐dwelling bird colonies on instream bacteria concentrations. Three bridges in central Texas were sampled under dry‐weather conditions for instream Escherichia coli. Two bridges were inhabited by migratory cliff swallows and one was devoid of birds. Numerous samples were collected from locations upstream, at the upstream bridgeface, and downstream of each bridge to determine whether significant increases in E. coli occurred in a downstream direction when birds were present. E. coli values increased significantly at bridgeface and downstream locations compared to upstream locations throughout the nesting season. During peak bird activity in May, bacteria geometric mean concentrations at bridgeface and downstream locations jumped from background levels <50 to >190 colony forming units (CFU)/100 mL, well above the state geometric mean criterion of 126 CFU/100 mL for primary contact recreation use. Results confirmed that under dry‐weather conditions bird colonies can have a significant impact on bacteria concentrations in the vicinity of the bridges they inhabit and therefore, to avoid this impact, monitoring should occur upstream of bridges.     

Population Dynamics of Escherichia coli in Surface Water1

Bucci, Vanni, Marin Vuli?, Xiaodan Ruan, and Ferdi L. Hellweger, 2011. Population Dynamics of Escherichia coli in Surface Water. Journal of the American Water Resources Association (JAWRA) 47(3):611‐619. DOI: 10.1111/j.1752‐1688.2011.00528.x Abstract: Present models of the fate of enteric bacteria in surface water usually assume simple first‐order decay. However, observed decay kinetics are typically biphasic and there is increasing evidence for growth in the ambient environment. These features are similar to the stationary phase of long‐term batch cultures, where the dynamics are the result of repeated cycles of population takeovers by Growth Advantage in Stationary Phase (GASP) mutants able to scavenge nutrients released from dead cells. We investigated the possible role of this mechanism (i.e., growth of an adapted subpopulation) in surface water using laboratory experiments with various strains of Escherichia coli in different types of water. Addition of ampicillin (which only kills dividing cells) to these cultures caused a decrease in the total cell density, demonstrating the presence of a growing subpopulation. Furthermore, long‐term survivors from surface water cultures outcompete naïve cells and take over the population in surface water. This growth advantage is heritable (i.e., aged strains were isolated from a single cell) and consistent with the GASP mechanism, although the responsible loci were not identified. Our results show that E. coli populations in surface water are dynamic and consist of dying naïve cells and growing surface water adapted cells. These results can explain the apparent biphasic decay pattern observed in laboratory experiments. This mechanism may also be important in the ambient environment.     

Common Snapping Turtles (Chelydra serpentina) as a Source of Fecal Indicator Bacteria in Freshwater Systems1

Habersack, Mathew J., Theo A. Dillaha, and Charles Hagedorn, 2011. Common Snapping Turtles (Chelydra serpentina) as a Source of Fecal Indicator Bacteria in Freshwater Systems. Journal of the American Water Resources Association (JAWRA) 47(6):1255–1260. DOI: 10.1111/j.1752‐1688.2011.00572.x Abstract: The United States Total Maximum Daily Load program is required by Section 303(d) of the Clean Water Act to clean up waters that do not meet state water quality standards. While conducting research into the bacterial composition of semiaquatic mammal feces, the opportunity presented itself to quantify commonly used pathogen indicator bacteria in the gastrointestinal contents from an ectothermic (cold‐blooded) animal, the common snapping turtle. Indicator bacteria concentrations were on the order of 10⁶ CFU/g feces (dry weight basis). The estimated bacterial loadings from this study demonstrate that the common snapping turtle, if present in sufficient numbers, may contribute significant bacterial loadings to waterways and should be considered when developing bacterial Total Maximum Daily Loads and in other bacterial water quality assessments.