Abstract
Transport of Escherichia coli (E. coli) through soil to drinking and recreational water may pose a serious health risk. The objective of this study was to determine how initial preferred soil wetting state influences the preferential transport of E. coli in a clay soil. A strain of E. coli marked with green fluorescent protein (gfp) was gravity-fed-sprinkler-applied as simulated rainfall to three replicates in different wetting states, along with Cl- and adsorptive dye near Plenty, SK. Canada. After 48 h, a 50 × 50 × 50 cm3 block was excavated to determine the transport pathways. Digital image analysis of horizontal sections provided estimates of dye coverage. Escherichia coli were significantly filtered in the top 10 cm of soil with concentration profiles similar to that of Cl-. Ratios of E. coli to Cl- did not show significant differences among treatments (P < 0.05) and indicated that below 10 cm depth, E. coli and Cl- were preferentially transported along the same pathways with no significant difference between plots. Results show that the majority of E. coli and Cl- were filtered when transported through the discontinuous pores of the near-surface matrix and suggest a saturated layer that controlled infiltration into organized root channels, resulting in preferential flow. Key words: Preferential flow, Escherichia coli, wetting state, Vertisol, conducting areas
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