Release Rates of Manure-Borne Coliform Bacteria from Data on Leaching through Stony Soil

groundwater (McMurry et al., 1998). A substantial body of literature exists describing leaching of microorgaManures are sources of several human pathogens that can potennisms through soil. Early studies documenting subsurtially contribute to surface and groundwater contamination. Microorganisms must first be released from the manure matrix before they face bacterial transport from septic effluents were recan infiltrate into and leach through the vadose zone. The objective viewed by Hagedorn et al. (1981) and Bitton and Harvey of this study was to estimate rates of rainfall-induced release of fecal (1992). These studies describe bacterial transport from coliform (FC) from surface-applied bovine manure. Simulated rainfall a few meters to 830 m, depending on soil or sediment of 7.1 cm h 1 was applied to the surface of 90-cm-long lysimeters filled texture and permeability, water saturation degree, and with the undisturbed stony soil. When the steady state was reached, length of time. More recent studies have quantified the clumps of manure were placed on the surface. Rainfall was continued leaching potential of fecal bacteria and genetically modifor about 5 h after application of manure, and 10-min leachate portions fied bacteria. Although leaching rates were influenced were analyzed for turbidity and FC. The convective–dispersive equato some extent by all soil and microbial properties, the tion with linear adsorption–exclusion and the first-order removal– regrowth terms was used as a model of the coliform transport in soil. predominant factors in disturbed soil cores appear to Asymptotic properties of the solution of this equation with the expobe soil structure and texture and porosity and bulk dennentially decreasing boundary concentration were used to infer the sity, in conjunction with bacterial size (Gannon et al., release rate constant from the FC breakthrough curves. A value of 1991a,b; Huysman and Veerstraete, 1993; Tan et al., 0.0054 0.0015 min 1 was found for the FC release rate constant. The 1991). In intact soil cores, distribution and continuity of regression line of reduced coliform concentrations on reduced turmacropores (preferential flow pathways) in conjunction bidity values was not significantly different from the one-to-one line; with initial water content appeared to be the predomiR 2 was 0.807. Assuming that turbidity can be used as a measure nant factors (Abu-Ashour et al., 1998; McMurry et al., of concentration of manure particulates in leachates, we found that 1998; Paterson et al., 1993). In general, higher leaching average values for the release rate constants were not significantly rates were observed in undisturbed soils as compared different for FC and manure particulates. The average velocity of bacteria and manure particulates transport was about seven times larger with disturbed soils (Smith et al., 1985; van Elsas et al., than the average pore velocity. The proposed technique of estimating 1991), presumably due to the destruction of macropores FC and manure release rates shows promise for use in further studies during the repacking of soil. needed to elucidate and assess factors affecting release rate. The majority of studies of pathogen bacteria transport in soils used bacterial cells that were suspended in solutions and then applied to soil surface or mixed with the T is growing concern regarding the potential influent solution (Bitton et al., 1974; Abu-Ashour et al., for contamination of surface and ground water by 1998; Devare and Alexander, 1995; Goldschmid et al., pathogens from bovine manures. Even though they are 1973; Gannon et al., 1991a,b; Germann et al., 1987; Henconsidered to be a beneficial fertilizer and soil amenddry et al., 1999; Hekman et al., 1995; Huysman and Verment, bovine manures are a substantial agricultural source straete, 1993; Hornberger et al., 1992; Lahlou et al., 2000; of several human parasites/pathogens. Escherichia coli Paterson et al., 1993; Smith et al., 1985; Tan et al., 1991; O157 and other EHEC strains are commonly found in van Elsas et al., 1991). Results of those studies are only beef and dairy cattle (Bos taurus L.) (Elder et al., 2000; partly applicable to microbial leaching from either landHancock et al., 1998; Porter et al., 1997). On-farm moniapplied or naturally deposited manures, since microortoring of E. coli O157:H7 suggests that shedding occurs ganisms must first be released from the manure matrix episodically (up to 105 organisms g 1 feces) and can perbefore they can infiltrate into and leach through the soil sist for variable periods of time ranging from about 1 profile. We are not aware of any data on bacteria release to 5 mo (Shere et al., 1998; Zhao et al., 1995). rates from manure subject to rainfall, and could find Pathogens applied onto soil surfaces may enter the only one recent paper (Bradford and Schijven, 2002) soil and travel through the vadose zone until they reach that contains data on manure dissolution in laboratory conditions. It is not known whether rates of manure D.R. Shelton, Y.A. Pachepsky, and J.S. Karns, U.S. Dep. of Agriculdissolution and bacteria release can be equated since ture, Agricultural Research Service, Animal and Natural Resources the bacteria distribution within manure material has Institute, Animal Waste Pathogens Laboratory, Bldg. 173, BARCnot been studied. At the same time, knowledge of the East, 10300 Baltimore Ave, Beltsville, MD 20705-2350; A.M. Sadeghi, U.S. Dep. of Agriculture, Agricultural Research Service, Animal and release rates is a precondition of bacteria and manure Natural Resources Institute, Environmental Quality Laboratory; W.L. transport simulations. Stout and W.J. Gburek, U.S. Dep. of Agriculture, Agricultural ReThe objective of this study was to estimate rates of search Service, Pasture Systems and Watershed Management Refecal coliform and manure release due to rainfall action. search Laboratory. Received 6 Nov. 2002. Original Research Papers. V02-0069. *Corresponding author ([email protected]). Abbreviations: CFU, colony forming units; FC, fecal coliform; NTU, nephelometric turbity units. Published in Vadose Zone Journal 2:34–39 (2003).