Surface runoff transport of Escherichia coli after poultry litter application on pastureland

Escherichia coli transported in surface runoff from dissolution of applied poultry litter is a major variable in assessing fecal contamination of streams. However, the relative magnitude of the E. coli concentration from a specific poultry litter application and relative to the time lag between litter application and rainfall are not completely understood. This research investigated E. coli transport in runoff on fourteen 2 m × 2 m pastureland plots. Poultry litter was manually applied (4,942 kg ha ^-1) in twelve plots followed by artificial rainfall with intensities equivalent to 2-year and 5-year storm events. Rainfall was applied in duplicate plots immediately after poultry litter application and 24 and 120 h after litter application. Experiments were also conducted on two control plots without poultry litter application. Surface runoff was collected using a flume installed in a trench. E. coli was quantified from sampled runoff and used as an indicator of fecal contamination by the most probable number (MPN) technique. No significant differences were observed in average event mean concentrations (EMCs) relative to storm intensity. Statistically significant differences were observed in average EMCs relative to time lag between litter application and rainfall. A nonlinear relationship was observed between average E. coli EMC and time lag, with the EMC decreasing between 0 h (1.6 × 10 ⁵ MPN/100 mL) and 24 h (1.3 × 104 MPN/100 mL) and then increasing at 120 h (4.3 × 104 MPN/100 mL). E. coli were always detected in the control plots (average EMC of 6.8 × 10 ³ MPN/100 mL), indicating the presence and transport of fecal bacteria from sources independent of the immediate poultry litter application. Even though poultry litter application may increase E. coli concentrations in runoff, other sources of fecal contamination serve as a significant component of the total E. coli EMC, especially as the time lag between litter application and rainfall events increases.