Submitted to: Letters in Applied Microbiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/5/2006
Publication Date: 2/1/2007
Citation: Guber, A.K., Karns, J.S., Pachepsky, Y.A., Sadeghi, A.M., Van Kessel, J.S., Dao, T.H. 2007. Comparison of release and transport of manure-borne E. coli and Enterococci under grass buffer conditions. Letters in Applied Microbiology. 44(2):161-167. Interpretive Summary: Escherichia coli and enterococci are common indicator organisms used to detect potential fecal contamination of surface and ground water and to determine water quality. Coupled monitoring of both organisms demonstrated differences in dynamics of their concentrations in waters that were reached by fecal contamination. Little if anything is known about the differences in the transport characteristics of the two indicator organisms in soil, or about the differences in their transport in overland flow. If differences in the transport of E. coli and enterococci exist, that may substantially affect the efficiency of using these organisms as indicators of fecal contamination from agricultural lands. The objective of this work was to test the hypothesis that E. coli and enterococci have similar patterns of release from animal feces and subsequent transport in the environment. The bacteria release and transport experiments in this work consisted of application of bovine manure with added bromide salt on the upper part of grass-covered turfgrass soil in experimental boxes followed by continual sampling of the runoff water and water infiltrated through soil during the simulated rainfall. Concentrations of E. coli, Enterococci, bromide, and turbidity were determined in the collected water samples. Novel construction of the boxes allowed us to separate the effect of release rates and from the effects of differences in consequent transport. Significant differences in release kinetics of E. coli and enterococci were found. A change in the type of the release kinetics s after 1 h of rainfall simulation was observed. No differences in the transport characteristics of the two organisms were observed because the 1.5-m distance appeared to be sufficient to bring the concentrations of the organisms released from the simulated cowpat to runoff and infiltration water to the background levels. Such differences may be pronounced in conditions where infiltration is less dominant, i.e. either soil is sealed or soil water content is high. The concentrations at the source of release need to be monitored to discern the differences in organisms’ release from differences in their transport.
Technical Abstract: Aims: To test the hypothesis that Escherichia coli and enterococci bacteria have similar release rates and transport characteristics after being released from land-applied manure. Methods and Results: Turfgrass soil sod was placed into 200-cm long boxes that had the top 25-cm sections separated to monitor the release and infiltration of bacteria which affected bacteria transport in the rest of the box. Dairy manure with added KBr was broadcast on the top section and on the upper 25-cm section of the rest of the slope. Boxes with either live or dead grass stand were placed under rainfall simulator for 90 minutes. Runoff and infiltration samples were collected and analyzed for Br, E. coli, enterococci and turbidity. Significant differences in release kinetics of E. coli and enterococci were found. A change from first-order release kinetics to zero-order kinetics after 1 h of rainfall simulation was observed. Conclusion: Differences in release rates but not in the subsequent transport were observed for E. coli and enterococci. Significance and Impact of the Study. Because both E. coli and enterococci are currently used as indicator organisms for manure-borne pathogens, the differences in their release rates may affect the efficiency of using these organisms as indicators.