TRANSPORT AND RETENTION OF MANURE-BORNE COLIFORMS IN SOIL COLUMNS

Authors: GUBER, ANDREY - ARS VISITING SCIENTIST; Shelton, Daniel; Pachepsky, Yakov

Submitted to: Vadose Zone Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/10/2005
Publication Date: 6/12/2005
Citation: Guber, A.K., Shelton, D.R., Pachepsky, Y.A. 2005. Transport and retention of manure-borne coliforms in soil columns. Vadose Zone Journal. Vol.4:828-837

Interpretive Summary: There is increasing concern regarding the potential for contamination of potable and recreational waters by manure-borne pathogens. Previous research indicates that beef/dairy cattle can excrete a variety of bacterial pathogens, such as E. coli, Salmonella and Clostridium. Since manures are frequently applied to soils or naturally deposited by grazing animals, there is concern that pathogens can inadvertently contaminate water supplies via runoff or leaching. Previous studies conducted with pure strains of bacteria suggest that bacteria readily attach to soil, thereby limiting leaching to groundwater. However, since pathogens are excreted with manure, they will be transported simultaneously with other manure constituents. Consequently, manure could affect the leaching of pathogens through the soil profile. A study was conducted to elucidate the effects of manure and leaching rate on bacterial transport though soil. E. coli and different manure dilutions were leached through soil columns with different leaching rates. E. coli attachment to soil was affected both by manure concentration and leaching rate. Attachment was diminished at higher manure concentrations due to competition for attachment sites and at higher leaching rates due to reduced contact time with soil. These findings indicate that manure facilitates pathogen leaching though soils. 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: Manure is a source of several bacterial pathogens that can potentially contribute to surface and ground water contamination. Results from most bacterial transport studies in soils are only partially applicable to manure-borne bacteria because microorganisms are released along with manure particulates as manure dissolves. We hypothesized that manure could enhance bacterial transport in soils due to competition for adsorption sites, thereby limiting attachment, and as a colloidal carrier. To test these hypotheses, breakthrough column experiments were conducted with undisturbed, 20-cm long Tyler silt loam columns from A horizon. A pulse of 4 % filtered bovine manure solution with E. coli and KCl was passed through columns. E. coli concentrations, chloride content and turbidity were measured in influent and in effluent. Columns were cut into 2-cm layers after the experiment to measure (i) viable bacterial concentrations in pore solution and attached to soil, (ii) bulk density, and (iii) water content. Companion batch experiments were carried out to measure attachment of E. coli to soil in the presence of various amounts of manure. E. coli attachment to soil decreased with increased manure content due to increased competition for attachment sites. Flow velocity affected E. coli transport and attachment to soil; there was relatively more attachment at slower flow velocity than at higher flow velocity. The distribution of E. coli between pore solution and soil particles in soil after high flow velocity experiments was similar to that in the batch experiments with the 4% manure suspension. Attachment in the batch experiments with 0% and 2% manure bracketed the attachment observed in the slow-flow columns after the breakthrough experiment. These data indicate that the presence of manure enhances E. coli transport in soil.