Submitted to: Water Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/21/2011
Publication Date: 11/22/2011
Citation: Jenkins, M., Endale, D.M., Fisher, D.S., Adams, P., Lowrance, R.R., Newton, L., Vellidis, G. 2011. Survival dynamics of fecal bacteria in ponds in agricultural watersheds of the Piedmont and Coastal Plain of Georgia. Water Research. 46:176-186. Interpretive Summary: Animal agriculture in watersheds can be a source of manure bacteria that can contaminate surface waters and put public health at risk. Because of the expanding urban-agriculture interface preventing surface water contamination with manure pathogens such as Salmonella and pathogenic E. coli is important for sustaining surface water quality. USDA-ARS scientists at the J. Phil Campbell, Sr., Natural Resource Conservation Center, Watkinsville, GA, in collaboration with scientists at the USDA-ARS Southeast Watershed Research laboratory, Tifton, GA, and the University of Georgia, Tifton, GA focused on stream impoundments or ponds as a mechanism of exposing manure pathogens to natural disinfection processes such as solar radiation, and attrition by their being consumed by predatory protozoa. The scientists examined three ponds in agricultural watersheds, one in the Southern Piedmont, and two in the Coastal Plain of Georgia. Concentrations of fecal indicator bacteria, E. coli and fecal enterococci, and pathogenic Salmonella and E. coli were determined for pond inflow, within pond, and pond outflow, and pond sediments. Experiments to determine residence times for the pond in the Southern Piedmont were undertaken and they indicated that bacteria entering the pond could be exposed to natural disinfection processes for several weeks. The pond in the Southern Piedmont effectively decreased the inflow concentrations of fecal bacteria; the ponds in the Coastal Plain, however, did not. Because of extensive drought, and unlike the pond in the Southern Piedmont, the in- and outflow at the ponds in the Coastal Plain was ephemeral, and ceased for several months. Nutrient concentrations at the two ponds in the Coastal Plain were significantly greater than the pond in the Southern Piedmont and may also account for the differences in their capacity to remove fecal bacteria and improve sown stream water quality. Concentrations of E. coli in sediments at the three ponds were significantly less than the fecal enterococci indicating that sediments under conditions of storm flow be more of a source of fecal enterococci than E. coli. Salmonella and pathogenic E. coli were detected and measured in all three ponds, and at times when concentrations of the fecal indicator bacteria were below the criterion that would indicate the presence of the manure pathogens. These results indicated that impounds in watersheds containing animal agriculture with continuous in- and outflow may improve down stream water quality.
Technical Abstract: Animal agriculture in watersheds can be a source of manure bacteria that can contaminate surface waters and put public health at risk. Because of the expanding urban-agriculture interface preventing surface water contamination with manure pathogens is important for sustaining surface water quality. We measured fecal indicator bacteria (commensal Escherichia coli and fecal enterococci) and manure pathogens (Salmonella and E. coli 0157:H7), and physic-chemical parameters in pond inflow, within pond, pond outflow, and pond sediments in three ponds in agricultural watersheds once a month for 30 months. Bishop Pond was located in the Southern Piedmont and Ponds A and C in the Coastal Plain of Georgia. Bromide and chloride tracer experiments were undertaken at Bishop Pond to determine baseflow residence time. Tracer data reflected a residence time much greater than the residence time estimated by two models, and indicated that complete mixing within the Bishop Pond was never obtained. The long baseflow residence time meant that fecal bacteria were exposed to solar UV-radiation and microbial predation both known to be factors in the inactivation of fecal indicator bacteria. At Bishop Pond outflow concentrations of fecal indicator bacteria were significantly less than inflow concentrations. Because of extensive drought in- and outflow at Ponds A and C was ephemeral. In contrast to Bishop Pond no differences in inflow and outflow concentrations of fecal indicator bacteria were observed. Both Salmonella and E. coli 0157:H7 were measured when concomitant concentrations of commensal E. coli were below the criterion for surface water impairment further indicating problems with the effectiveness of indicator organisms. Bishop Pond with continuous inflow and outflow improved down stream water quality. The drought conditions and ephemeral inflow and outflow of Ponds A and C, and possibly greater nutrient concentrations within the two ponds appeared to make them less effective at improving down stream water quality.