Monday, November 13, 2006

Effect of Manure on Escherichia Coli Attachment to Soil Fractions.

Andrey Guber1, Y.A. Pachepsky2, D.R. Shelton2, and Olivia Yu2. (1) Dept of Earth and Environmental Sci, Univ of California, A135 Bourns Hall, Riverside, CA 92521, (2) USDA-ARS-BA-ANRI-EMSL, Bldg. 173, Rm. 203, BARC-EAST, Powder Mill Road, Beltsville, MD 20705

Escherichia coli are commonly used as indicators of fecal contamination in the environment. Attachment of bacteria to soil and sediment is an important retardation factor of bacterial transport with runoff water. Despite the fact that E. coli are derived exclusively from feces/manure, the effect of the presence of manure colloids on bacteria attachment to soil fractions has never been directly studied.  The objective of this work was to evaluate the magnitude of the effect of manure on E. coli attachment to soil fractions. The attachment to soil was studied in batch experiments with fractions of loam and sandy clay loam topsoil that were taken in Pennsylvania and Maryland. Sand fraction 0.063-0.125, 0.125-0.25, and 0.25-0.5 mm was obtained by wet sieving, while silt and clay fractions were obtained by sedimentation. Manure colloidal suspension (MCS) was obtained by a15-min centrifugation of 40 g L-1 liquid bovine manure suspension at 100xG. E. coli cells were added to DI water and to MSC to create four concentration levels. Water-E. coli suspensions and the MCS were equilibrated with air-dry soil fractions at soil-suspension ratios of 1:10, and centrifuged for 15 min at 100xG. E. coli content, pH and EC were measured in the supernatant and applied solution. In water suspension, E. coli attachment to sand fractions was less than to fine fractions for Maryland soils. No difference was found for the Pennsylvania soil. Manure addition significantly decreased in E. coli attachment to all soil fractions, possibly because of the increase in pH and in EC of the suspensions. The lowest E. coli attachment occurred in the Maryland loam soil from MSC. The presence of manure can decrease E. coli attachment to soil and sediment in runoff and facilitate E. coli overland transport.