Saturated and unsaturated transport of cow manure-borne Escherichia coli through in situ clay loam lysimeters

Despite relatively extensive laboratory trials, in situ research on transport of bacteria through layered soil is surprisingly lacking. We investigated the in situ transport of cow manure-borne Escherichia coli through a naturally layered clay loam soil profile, under saturated and unsaturated steady flows. Lysimeters (22 cm diameter and 50 cm height) were inserted vertically into the field soil. Water flow through the columns was controlled by a tension infiltrometer by imposing inlet matric suctions of 5 and 0 cm for the unsaturated and saturated conditions, respectively. When the steady-state flow was established, cow manure was applied on the lysimeters’ surface at the rate of 10 Mg ha−1 (dry basis). Soil solution was sampled during leaching at two depths (20 and 40 cm) at 1, 2, 4, 6, 12, and 24 h after manure application. Concentrations of the bacteria in the influent (C0) and soil solution (C) samples were determined. Bacterial filtration coefficients (λf) and relative adsorption indices (SR) were calculated for each flow condition and soil depth. Flow condition, sampling depth and their interaction had significant effects (P < 0.05) on the C and C/C0 values for all leaching times except at 24 h. At 24 h only the flow condition affected significantly the C and C/C0. Flow condition and depth affected the λf and SR. Maximum and minimum values of λf were calculated for the unsaturated condition/first depth and saturated condition/first depth combinations, respectively. The unsaturated λf was nearly 34% greater than the saturated λf. Although the topsoil had significant bacterial filtration capacity, equivalent filtration was measured for the deeper strata. Overall, variation of texture and structure along the in situ soil profile effectively altered the bacteria movement.