Release, Dispersion, and Resuspension of Escherichia coli From Direct Fecal Deposits Under Controlled Flows

Water-quality standards have been placed on fecal indicator organisms such as Escherichia coli in an attempt to limit the concentrations in water bodies. Cattle can be a significant source of bacteria to water systems, particularly when they are allowed direct access to streams. A flume study was conducted to quantify the effect and understand the transport of E. coli from directly deposited cattle manure. Five steady-state flows, ranging from 0.00683 to 0.0176m3/s, were studied and loads from a single cowpie exceeded the U.S. Environmental Protection Agency's recommended water-quality standards (235CFU/100ml) at each flow over the hour study period. Average E. coli concentrations ranged from 102 to 105CFU/100ml over the hour sampling period for all flows. High spatial variations in E. coli concentrations were often seen at each sampling time, with higher concentrations typically at the bottom of the flume. E. coli resuspension was initially greater at 0.5min after deposition, for the lowest flow (105CFU/m2/s); however, resuspension rates became similar over time, on the order of 103CFU/m2/s. This study demonstrates that the concentrations of E. coli can vary over the water column, and therefore grab samples may inaccurately measure bacteria concentrations and loads in streams. In addition, resuspension rates were often high, so the incorporation of this process into water-quality models is important for bacteria prediction.