Bacterial Mobility Facilitated By Soil Depth And Intact Structure

Pathogenic bacteria, widely present in septic tanks, sewage sludges, and wastewater, can move through the subsurface environment to pollute drinking water. Bacterial transport behaviors vary with soil properties and are subject to soil pore networking. In this study, we investigated the transport of Escherichia coli 652T7 through intact and disturbed soils collected from different soil depths (0-5 cm, 5-10 cm, 10-15 cm, and 15-20 cm). The results obtained under steady-state saturated flow conditions demonstrated significant influences of soil depth and soil structure on the transport of E. coli 652T7. The breakthrough percentages of E. coli 652T7 from the intact soil cores increased with soil depth from 36 % at 0-5 cm to 63 % at 5-10 cm, 83 % at 10-15 cm, and 100 % at 15-20 cm. A similar trend was observed for the breakthrough from the repacked soil cores except with lower percentages (i.e., 16 % at 0-5 cm, 49 % at 5-10 cm, 76 % at 10-15 cm, and 86 % at 15-20 cm). Such an increase with soil depth was attributed to a combined effect of decreases in soil organic matter content (from 3.84 % to 2.47 %), free iron oxides (from 142.25 mg kg(-1) to 110.66 mg kg(-1)), and zeta potential (from -17.6 mV to -29.0 mV) with soil depth. The larger breakthrough percentages of E. coli 652T7 from the intact than the repacked soil cores are speculated due to the existence of larger macropores, lower pore connectivity density, and reduced access to attachment sites in the intact soils than in the disturbed soils. Overall, this study suggests that tillage and organic amendments might be effective measures for reducing bacterial movement in soils.