Modeling Transport of Escherichia coli from Soil into Overland Flow Under Raindrop Impact

Abstract:

Raindrop impacted transport of Escherichia coli (E. coli) from soil into overland flow is an important but poorly understood process. Research has focused on the attachment of E. coli to solids, E. coli transport in percolating water through soil, in overland flow over bare ground or through vegetation, and of E. coli release from cowpats during rainfall. However, E. coli transport from soil under splash erosion has not been well studied. A small scale rainfall experiment was conducted in which E. coli was mixed with simple soils composed either entirely of sand (250-300 µm) or a 9:1 sand-clay mixture. A variation on the conceptual Hairsine-Rose erosion model was applied to the experiment to help understand the transport processes. Although previous research has documented E. coli attachment to dislodged soil during rainfall, the presence of clay in our experiments did not noticeably affect the total amount or timing of E. coli ejected from the soil; we were not able to determine bacterial attachment to the clay. Our findings suggest that best management practices used to reduce the energy of raindrop impact, such as vegetated buffers, are likely effective for reducing E. coli as well.