Interaction of Escherichia coli and Soil Particles in Runoff

Abstract

A laboratory-scale model system was developed to investigate the transport mechanisms involved in the horizontal movement of bacteria in overland flow across saturated soils. A suspension of Escherichia coli and bromide tracer was added to the model system, and the bromide concentration and number of attached and unattached E. coli cells in the overland flow were measured over time. Analysis of the breakthrough curves indicated that the E. coli and bromide were transported together, presumably by the same mechanism. This implied that the E. coli was transported by advection with the flowing water. Overland-flow transport of E. coli could be significantly reduced if the cells were preattached to large soil particles (>45 m). However, when unattached cells were inoculated into the system, the E. coli appeared to attach predominantly to small particles (<2 m) and hence remained unattenuated during transport. These results imply that in runoff generated by saturation-excess conditions, bacteria are rapidly transported across the surface and have little opportunity to interact with the soil matrix.The transport of microorganisms from agricultural land into waterways can have detrimental effects on water quality and human health (10,18,28,29). To develop robust strategies to control the passage of microorganisms to waterways, a good understanding of the transport mechanisms involved is required. In a study of pig slurry flowing down a slope, it was reported that all of the bacteria were absorbed and retained by the soil under relatively dry antecedent conditions (9). In contrast, studies with saturated soils often show poor removal of bacteria (4, 5). This can be attributed, in part, to a lack of infiltration, which limits interaction of runoff with the soil matrix (1, 3).A further important factor in determining bacterial transport in overland flow is the state in which the bacteria occur, with different transport mechanisms postulated for bacteria attached to soil particles, present in flocs of cells, or occurring as single cells (11,16,28). It has been calculated that bacteria would need to be attached to soil particles Ͼ63 m in diameter to settle out of overland flow and would need to be in large flocs Ͼ500 m in diameter before they could be filtered out by grasses (11). In studies with artificial cowpats under simulated rainfall conditions, it was found that Escherichia coli cells were not eroded in flocs and that only 8% were attached to particles (21). These findings imply that E. coli eroded from cowpats during rainfall events would, under saturation-excess conditions, be rapidly transported over the soil surface unless it can attach to large soil particles during the transport process.There have been numerous studies on the attachment of bacteria to particles in marine waters, but only a small number with freshwater systems (8). In storm water from urban land, fecal indicator bacteria were adsorbed predominantly to fine clay particles (Ͻ2 m) (6). In another study with urban storm water, 83% of fecal coliforms...

Evidence for Coexistence of Distinct Escherichia coli Populations in Various Aquatic Environments and Their Survival in Estuary Water

“…Interaction with particles is a major factor influencing the fate of E. coli in water and sediment (20,47,48). Nevertheless, in this study, the ability to form a biofilm on a plastic surface did not explain the extended survival abilities of E. coli strains in water, which was probably because the test did not recreate the environmental conditions.…”

Variability of E. coli density and sources in an urban watershed

“…Spearman correlation analysis showed that only TSS was significantly correlated with E. coli (r ¼ 0.299, p ¼ 0.022) and enterococci (r ¼ 0.404, p ¼ 0.006), which suggested that TSS might have a better relationship than other variables (such as TP, N-NO 2 /NO 3 ) with E. coli density. It is reasonable because bacteria are likely to attach to the fine particles (o2 mm) and move rapidly to receiving waters during rainfall (Muirhead et al 2006). An early study (Davis et al 1977) showed that microorganisms and suspended solids in stormwater run-off were significantly correlated.…”

Effect of vegetated filter strips on infiltration and survival rates of Escherichia coli in soil matrix at Mau, Njoro River Watershed, Kenya

“…E. coli loading in overland flow was directly related to the E. coli concentration in the soil matrix. In this study, five reasons can be attributed to these observations: First, the concentration of E. coli in runoff was in the order of 4 log (CFU) mL -1 compared to the concentration of E. coli in runoff in the order of 2 to 3 log (CFU) mL -1 in simulated experiment for the short duration rainfall of 5 min (Ling et al 2009); secondly,\25% of E. coli was isolated from feces mixed with soil, which was a low attachment level compared to [50% of E. coli attached to feces alone (Muirhead et al 2005;Muirhead et al (2006); thirdly, the physical filtration of bacteria at the soil surface also increased the chances of losses during runoff (Crane et al (1983); fourth, in overland flow, more than 50% of bacteria were not settled or filtered (Schillinger and Gannon 1985); fifth, the use of soil trays (where the fecal material source contains mostly organic material with low density) is more erodible than grassed vegetated filters on soil surface rather (Khaleel et al 1979). Thus, VFS on soil surface provided a better design for research and management of soils for the control of manure borne pathogens in rangelands and agro-pastoral systems.…”

“…Limited data on infiltration rates of manure borne pathogens in overland flows into soil matrix and their survival rates in these microhabitats limit our understanding of the dynamics of microbial pathogens' fate and transport in overland flows (Tyrrel and Quinton 2003;Muirhead et al 2006). Conservation of Escherichia coli mass balance in overland flow is controlled by fecal coliforms population dynamics, attenuation and diffusion (Tian et al 2002).…”