| 15 Oct 2025
Modeling E. coli fate and transport in and around a cattle pond
Abstract. Contamination of surface water is a concern for public health. Lands used for animal production are sources of fecal microorganisms that can reach water bodies, impact their quality, and adversely affect their potential uses. Understanding the mechanisms of microbial transport through surface/subsurface flow is imperative to predict surface water contamination and to assign management strategies for enhanced water quality. The aim of this work to develop and test a mechanistic numerical model to simulate watershed-scale surface/subsurface water flow, bacteria release from cow manure, and their fate, as well as transport to a cattle pond. The integrated surface-subsurface hydrological platform HydroGeoSphere (HGS) was the basis for the site-specific model. The pond and its environs were monitored for 15 months for E. coli concentrations, which remained relatively high throughout the study The model was applied to simulate Escherichia coli (E. coli) bacteria transport in a grassed drainage basin grazed by a permanent herd of approximately 50 cattle. Most model parameter values were adopted from the literature. The model explicitly accounted for cow excretion to the pond as a source of microbial contamination. The latter was estimated from the time spent by cows in the pond, which in turn was estimated from imagery obtained with eight trail cameras installed to cover the pond surface. Images were obtained every 15 min. Simulations for two years showed that the non-calibrated model replicated spatiotemporal patterns and peak E. coli concentration reasonably well. The E. coli cumulative flux loaded by cattle excretion directly to the pond was around two orders of magnitude greater than that with the surface flow. The results of this work indicate the opportunity and show the approach to obtaining a moderately accurate forecast of microbes in cattle ponds using only readily available data.
The paper entitled “Modeling E. coli fate and transport in and around a cattle pond” deals with pond water contamination by cattle. The authors developed and tested a mechanistic numerical model to simulate watershed-scale surface/subsurface water flow, bacteria release from cow manure, and their fate, as well as transport to a cattle pond. The paper is generally well written but need some clarifications as listed below.
My main comment is about the consideration of suspended sediment in the model. As bacteria are mostly transported with eroded soil and manure particles, and as it can survive longer in the sediment, I would expect a more thorough discussion on bacteria and sediment. It is not clear to me (1) how the authors considered the effect of sediment and bacteria resuspension by, e.g., cattle trampling, on bacteria concentration in water, and how they simulated soil and manure erosion along with suspended sediment settling and resuspension, and (2) if the authors considered different die-off rates for water column, soil, and pond sediment.
L52 “postharvest processing” not clear
L70 “so the scope of the problem is not well known” not clear
L248-249 This sounds more like method
L256 “each year” as fare as I understand, only 1 winter period was monitored, not clear
L261 a verb is missing
L274 “keep the pond from emptying” not clear
L278 “Simulations show that it usually occurs during and after rain events” What does the authors mean? Surface runoff occurring during and after rainfall events is rather obvious. The number of days with rainfall was small? Some rainfall events do not generate surface runoff in the catchment, depending on rainfall typology and soil antecedent conditions?
L285-296 does it mean that, in the model, surface runoff also occurs when there is no rain? Do the authors call “runoff” the surface runoff or the overall water yield to the pond? Besides, is the dam completely impervious?
L318 “Concentration in the pond source locations” is it what the authors call “interior locations” on L365?
L324-325 What was the sampling protocol regarding the presence of cows in the pond or on the shores at sampling time? Were some samples taken in the vicinity of a cow that would resuspend sediment by trampling and mixing water?
L337, 338, 339 “shoulder” not clear. On L339, the point in “After the "shoulder" period. The” must be revised.
L355 “entering the pond by manure excretion” do the authors mean “by direct excretion of feces into the pond”, as suggested in L359? I would suggest a similar revision of the sentence on L420-421
L356-357 If I understand well the meaning, I would rephrase as such: “Simulations show that water flowed mainly from the pond into the subsoil, so that E. coli concentrations in the subsoil did not affect the water quality in the pond.”
L359, 363 remove capital C to “Coli”
L368-373 what about the role of temperature?