Modeling the release of Escherichia coli from soil into overland flow under raindrop impact

Abstract

a b s t r a c tPathogen transport through the environment is complicated, involving a variety of physical, chemical, and biological processes. This study considered the transfer of microorganisms from soil into overland flow under rain-splash conditions. Although microorganisms are colloidal particles, they are commonly quantified as colony-forming units (CFUs) per volume rather than as a mass or number of particles per volume, which poses a modeling challenge. However, for very small particles that essentially remain suspended after being ejected into ponded water and for which diffusion can be neglected, the Gao model, originally derived for solute transfer from soil, describes particle transfer into suspension and is identical to the Hairsine-Rose particle erosion model for this special application. Small-scale rainfall experiments were conducted in which an Escherichia coli ( E. coli ) suspension was mixed with a simple soil (9:1 sand-toclay mass ratio). The model fit the experimental E. coli data. Although re-conceptualizing the Gao solute model as a particle suspension model was convenient for accommodating the unfortunate units of CFU ml −1 , the Hairsine-Rose model is insensitive to assumptions about E. coli per CFU as long as the assumed initial mass concentration of E. coli is very small compared to that of the soil particle classes. Although they undoubtedly actively interact with their environment, this study shows that transport of microorganisms from soil into overland storm flows can be reasonably modeled using the same principles that have been applied to small mineral particles in previous studies.

Explaining and modeling the concentration and loading of Escherichia coli in a stream—A case study

“…As has been documented previously, E. coli concentrations were highly correlated with sediment concentrations and related variables, including total P (Gentry et al, 2006;Vidon et al, 2008). According to previous findings (Wang, 2015;Wang et al, 2017;Wang et al, 2018), one reason was that transport of E. coli and sediment can be explained by the same mechanisms, especially when stormwater dominates. The high correlation between the increase of E. coli level and the occurrence of storm and the increase of sediments (Table 5) was generally explained by surface erosion and the co-transport of E. coli both alone and bound to eroding sediments (Muirhead et al, 2006a;Oliver et al, 2005).…”

“…As E. coli was found to be eroded from the top soil (Wang, 2015;Wang et al, 2017;Wang et al, 2018) and resuspended from the bottom of the stream together with sediments (Ferguson et al, 2003;Jamieson et al, 2005), it was expected that E. coli concentrations were significantly positively correlated with PC1. As has been documented previously, E. coli concentrations were highly correlated with sediment concentrations and related variables, including total P (Gentry et al, 2006;Vidon et al, 2008).…”

Experimental and analytical studies of solute transport during run‐off over vegetated surfaces

“…The well‐known Hairsine–Rose model (Hairsine & Rose, ) assumed that small particle transfer from soil into overland run‐off through a shield layer. Wang et al () confirmed that the Gao model (Gao et al, , ) is identical to the Hairsine–Rose model (Hairsine & Rose, ) for simulating the transport of colloidal from soil into overland storm flows. Through these studies, researchers have gained a generally good understanding of the solute transport from soil into overland flow.…”

Release of Escherichia coli under raindrop impact: The role of clay

“…Muirhead et al (2006) looked at the interaction between E. coli and soil particles in overland flow across saturated soil and found that E. coli were mainly attached to mineral particles smaller than 2 µm and, once mobilized, E. coli remained in suspension. Using lab experiments, Wang et al (2017) studied mineral colloid and bacteria co-release from soil into overland flow under raindrop impact (splash erosion). They found that the temporal patterns of release of mineral colloid and bacteria were identical (Wang et al, 2017).…”

“…Using lab experiments, Wang et al (2017) studied mineral colloid and bacteria co-release from soil into overland flow under raindrop impact (splash erosion). They found that the temporal patterns of release of mineral colloid and bacteria were identical (Wang et al, 2017). But they were unable to specifically identify the role of clay in the E. coli release process (Wang et al, 2017).…”