Transport of Resistance‐labeled Escherichia Coli Strains Through a Transition Between Two Soils in a Topographic Sequence

Abstract

AbstractField experiments were conducted to determine the pathways and characteristics of bacterial transport through a saturated soil profile which represented a transition between the Steiwer (Ultic Haploxeroll) and Hazelair (Aquultic Haploxeroll) soil series and was located in a concave footslope position. Three separately distinguishable Escherichia coli strains were injected into three perforated horizontal lines installed upslope from the transition, and positioned in the A, B, and C horizons of the soil profile. Migration of the labeled strains was evaluated by collecting water samples from piezometers, sampling various depth zones in the soil, and placed in rows at various distances downslope. In addition, surface runoff samples were collected at the furthest upslope location of observed overland flow. Bacterial translocation patterns varied with depth of injection at the first sampling row downslope; however, as the bacteria penetrated into the transition zone, flow pathways converged and injection depth differences disappeared. Also, a transition from predominately matrix flow to predominately “pipe” flow was observed as the downslope flow of water was directed upward in the soil profile by hydraulic gradients and a restrictive clay layer. Translatory channel flow (“pipe” flow) demonstrated widespread influence through this transition and apparently large volumes of the water passing downslope were intercepted and conducted by these channels. This study provides the link joining results from previous reports and more completely describes septic‐system effluent migration on saturated hillslopes while additionally stressing the influence of pipe flow on hillslope hydrologic processes.