Submitted to: Vadose Zone Journal
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/6/2003
Publication Date: 3/1/2003
Citation: Shelton, D.R., Pachepsky, Y.A., Sadeghi, A.M., Stout, W.L., Karns, J.S., Gbarek, W.J. 2003. Release rates of manure-borne coliform bacteria from data on leaching through stony soil. Vadose Zone Journal. 2:34-39. Interpretive Summary: There is increasing concern regarding the potential for contamination of potable and recreational waters by manure-borne pathogens. For example, pathogenic E. coli in general, and enterohemorrhagic E. coli O157:H7 in particular, are serious health threats. Enterohemorrhagic E. coli O157:H7 causes bloody diarrhea and, if not treated promptly, can result in kidney failure and death. There are an estimated 73,000 cases of E. coli O157 infections per year in the U.S., of which approximately 11,000 are water-borne. Previous research indicates that dairy and beef cattle can harbor this organism without being affected and shed it in their feces. Since manures are frequently applied to soils or naturally deposited by grazing animals, there is concern that pathogenic E. coli can inadvertently contaminate water supplies via runoff or leaching. A study was conducted to mathematically model the release rates of fecal coliform bacteria (a surrogate for pathogenic E. coli) from cow manure and their ability to leach through highly fractured soils common to the Northeast U.S. Fecal coliform bacteria were readily released from fresh cow manure and quickly leached through three yards of subsoil. This findings indicate that manure-borne pathogens can potentially leach through these subsoils, however, the potential for contamination of ground water or surface water will also depend on many other factors including amount and timing of rainfall, distance to water reservoirs, and bacterial mortality rates.
Technical Abstract: Manures are sources of several human pathogens that can potentially contribute to surface and ground water contamination. Microorganisms must first be released from the manure matrix before they can infiltrate into and leach through vadose zone. The objective of this study was to estimate rates of rainfall-induced release of fecal coliform (FC) from surface-applied bovine manure. Simulated rainfall of 7.1 cm h-1 was applied to the surface of 90 cm-long lysimeters filled with the undisturbed stony soil, and, when the steady-state was reached, clumps of manure were placed on the surface. Rainfall was continued for about 5 hours after application of manure, and 10-min leachate portions were analyzed for turbidity and FC. The convective-dispersive equation with linear adsorption/exclusion and the first-order removal/regrowth terms was used as a model of the coliform transport in soil. Asymptotic properties of the solution of this equation with the exponentially decreasing boundary concentration were used to infer the release rate constant from the FC breakthrough curves. A value of 0.0054"0.0015 min-1 was found for the FC release rate constant. The regression line of reduced coliform concentrations on reduced turbidity values was not significantly different from the 'one-to-one' line; R2 was 0.807. Assuming that turbidity can be used as a measure of concentration of manure particulates in leachates, we found that average values for the release rate constants were not significantly different for FC and manure particulates. The average velocity of bacteria and manure particulates transport was about seven times larger than the average pore velocity. The proposed technique of estimating FC and manure release rates shows promise to be used in further studies needed to elucidate and assess factors affecting release rate.