Survival of E. Coli Delivered with Manure to Stream Sediment.

Concentrations of E. coli bacteria are mandated by EPA for water quality evaluation in designating impaired surface waters, and for design of management practices to prevent fecal contamination of water. Many of these management practices reduce runoff from agricultural fields, implying that manure is the source of E. coli when it enters stream water. Recent studies have shown that stream sediment acts as a reservoir and potential source of fecal bacteria. This study was conducted to determine if (a) E. coli survival in the presence of dilute manure (i.e., simulated runoff) was effected by sediment particle size distribution and organic matter content, and (b) temperature affects E. coli survival in sediments the same way as it affects E. coli survival in other environmental media. Laboratory experiments were conducted at three temperatures (4, 14, and 24 ºC) using stream sediment from an agricultural stream mixed with a manure slurry from the USDA-ARS Beltsville dairy farm. Stream conditions were statistically simulated using   innovative flow-through chambers. An oscillatory growth stage was observed during the first 4 to 7 days at all temperatures before the exponential inactivation stage began. The oscillation rhythm did not depend on temperature, but the population magnitude did. The E. coli inactivation rates slowed as the temperature decreased for the same sediment. The inactivation rates had the classical power law dependence on temperature during the exponential inactivation stages. Increases in both sediment clay content and in organic matter increased the initial E. coli growth and slowed the inactivation rates. At the lowest temperature, E. coli persisted for three months in sediment, suggesting that E. coli survival was possible in the stream sediment over winter. Sediment provides an effective hospitable secondary habitat for manure-borne E.coli with texture, organic matter content and temperature being the inactivation controls.