Evaluation of fecal indicator bacteria loadings from a wildlife point source and sediment resuspension in inland streams
The contamination of inland surface water by point and nonpoint sources is a widespread human health concern. To address this problem, a thorough understanding of the sources and persistence of this pollution is necessary. Using fecal indicator bacteria (FIB) as a surrogate for enteric pathogens, the Environmental Protection Agency (EPA) and state agencies have developed surface water quality standards. If a segment does not meet these standards, a Total Maximum Daily Load (TMDL) must be developed for the watershed to identify sources of bacterial pollution. Currently, FIB pollution is the leading pollution type addressed by TMDLs in the country.
One source of FIB identified in TMDLs is colonies of birds roosting under bridges. It has been proposed that the birds’ feces can augment the FIB concentrations downstream of bridges. In this year-long study of Bull Creek in Austin, Texas, it was determined that the concentrations of Escherichia coli and fecal coliform downstream of a bridge were significantly greater when migratory cliff swallows were nesting under the bridge. The downstream concentrations of both FIB exceeded contact recreation standards. Data also suggest that FIB from the feces could be swept into the stream by runoff from storm events. No enterococci loading was observed in conjunction with the swallows.
This study also investigated the affects of sediment resuspension on surface water FIB concentrations and the persistence of FIB in shady, inland streams. The resuspension of sediments with attached FIB could also increase the FIB concentration in the water column and increase its persistence. The results of reactor-based experiments demonstrated that the concentration of E. coli in water from an effluent-dominated stream increased by a factor of 3 when riverine sediments were resuspended and exceeded single sample standards for contact recreation, suggesting sediments as a reservoir of E. coli. Additionally, concentrations of E. coli decreased by approximately 90% and 70% over 2 days in reactors containing stream water and sediment-laden stream water, respectively.