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. 2002 Nov;68(11):5517-27.
doi: 10.1128/AEM.68.11.5517-5527.2002.

Transport of Cryptosporidium parvum oocysts through vegetated buffer strips and estimated filtration efficiency

Edward R Atwill  1 , Lingling Hou, Betsy M Karle, Thomas Harter, Kenneth W Tate, Randy A Dahlgren
Affiliations

Transport of Cryptosporidium parvum oocysts through vegetated buffer strips and estimated filtration efficiency

Edward R Atwill et al. Appl Environ Microbiol. 2002 Nov.

Abstract

Vegetated buffer strips were evaluated for their ability to remove waterborne Cryptosporidium parvum from surface and shallow subsurface flow during simulated rainfall rates of 15 or 40 mm/h for 4 h. Log(10) reductions for spiked C. parvum oocysts ranged from 1.0 to 3.1 per m of vegetated buffer, with buffers set at 5 to 20% slope, 85 to 99% fescue cover, soil textures of either silty clay (19:47:34 sand-silt-clay), loam (45:37:18), or sandy loam (70:25:5), and bulk densities of between 0.6 to 1.7 g/cm(3). Vegetated buffers constructed with sandy loam or higher soil bulk densities were less effective at removing waterborne C. parvum (1- to 2-log(10) reduction/m) compared to buffers constructed with silty clay or loam or at lower bulk densities (2- to 3-log(10) reduction/m). The effect of slope on filtration efficiency was conditional on soil texture and soil bulk density. Based on these results, a vegetated buffer strip comprised of similar soils at a slope of <or=20% and a length of >or=3 m should function to remove >or=99.9% of C. parvum oocysts from agricultural runoff generated during events involving mild to moderate precipitation.

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Figures

FIG. 1.
FIG. 1.
Raw data for discharge of C. parvum oocysts from overland flow. The slope was 5%, and the 4-h precipitation rate was 1.5 ml/cm2/h.
FIG. 2.
FIG. 2.
Raw data for discharge of C. parvum oocysts from subsurface flow. The slope was 5%, and the 4-h precipitation rate was 1.5 ml/cm2/h.
FIG. 3.
FIG. 3.
Modeled filtration efficiency of a 1-m vegetated buffer as a function of bulk density and percent slope with silty clay loam. The initial load was 3 × 107 oocysts.
FIG. 4.
FIG. 4.
Modeled filtration efficiency of a 1-m vegetated buffer as a function of bulk density and percent slope with loam. The initial load was 3 × 107 oocysts.
FIG. 5.
FIG. 5.
Modeled filtration efficiency of a 1-m vegetated buffer as a function of bulk density and percent slope with sandy loam. The initial load was 3 × 107 oocysts.
FIG. 6.
FIG. 6.
Modeled number of total oocysts in subsurface flow effluent as a function of infiltration rate, as predicted by the linear mixed-effects regression model. The initial load was 3 × 107 oocysts, stratified by soil type and precipitation rate (1.5 or 4.0 ml/cm2/h).
FIG. 7.
FIG. 7.
Observed number of total C. parvum oocysts in overland flow effluent compared to predictions generated by the linear mixed-effects regression model.
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References

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