Transport ofCryptosporidium parvumOocysts through Vegetated Buffer Strips and Estimated Filtration Efficiency

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 <20% and a length of >3 m should function to remove >99.9% of C. parvum oocysts from agricultural runoff generated during events involving mild to moderate precipitation.Cryptosporidium parvum has emerged as a widespread and persistent waterborne microbial pathogen, with specific genotypes able to be transmitted ambidirectionally between livestock and humans (e.g., amphixenotic) (6,42,46,54). Although we still do not know the percentage of annual cases of human cryptosporidiosis that are attributable to livestock-derived waterborne C. parvum (39), reducing the likelihood that animal agricultural operations will contaminate surface water with infective C. parvum oocysts will help safeguard both water quality and public health (51). Several strategies exist for minimizing the likelihood that an animal agricultural operation contaminates surface water with infective C. parvum oocysts. For example, one such strategy is to reduce the incidence of C. parvum infection or the intensity of fecal shedding of C. parvum oocysts by livestock populations, thereby reducing the rate of environmental loading of C. parvum per livestock unit (26,36). These herd-health efforts remain hampered by our poor understanding of the medical ecology of C. parvum within livestock populations (3,4,16,40), how to interrupt transmission between the biological reservoir and susceptible animals (3, 40), and the lack of an affordable vaccine that has been proven to be efficacious in commercial agricultural settings (23,47).A second strategy is to manage the manure produced by livestock so that the survivability and off-site transport of infective C. parvum are substantially reduced (3,20,30,53,55). One strategy being advocated for minimizing the transport potential of C. parvum oocysts from animal manure to surface water is to place vegetated buffer strips between animal agricultural operations and vulnerable surface water supplies (10,12,15,32,38,51,59,60). Optimal design criteria for on-farm vegetated buffer strips currently do not exist for waterborne microbial contaminants. Moreover, studies ...

Management reducesE. coliin irrigated pasture runoff

“…We calculated the percentage of total number (cfu) of E. coli retained within the wetland during each event from the difference between inflow and outflow load, and found that percent reduction ranged from 33% to 91%, with an average of 73% (table 1). These results are comparable to previous findings that relatively narrow (1 to 2 yards wide) vegetative buffer strips can reduce E. coli and C. parvum in runoff by as much as 90% to 99% on California's annual grasslands under rainfall-runoff conditions (Atwill et al 2002(Atwill et al , 2006Tate et al 2004Tate et al , 2006. Reductions of 80% to 99% have been seen for E. coli and fecal coliforms with the use of constructed surfaceflow wetlands to treat municipal and Top left, channelized runoff from the pasture was collected in a small basin.…”

“…This relationship can be attributed to the fact that higher runoff rates increase the tailwater's capacity for pollutant mobilization and transport. In other studies, we have found that runoff rate is positively correlated with the load of E. coli and C. parvum discharged from cattle fecal deposits on annual grasslands under rainfall-runoff conditions (Atwill et al 2002;Tate et al 2004Tate et al , 2006.…”

Climate and On-Farm Risk Factors Associated with Giardia duodenalis Cysts in Storm Runoff from California Coastal Dairies

“…These large fluxes of fecal coliforms suggest that enteric pathogens shed by infected cattle may also be present in runoff from similar high-cattle-use areas, given the abilities of bacterial and protozoal microorganisms shed in bovine feces to be eluted from fresh fecal matrices and entrained in overland flow during precipitation (2,3,5,8,27,28). Given the common occurrence of Giardia duodenalis in dairy cattle herds (21,22,30,31), the apparent low infectious dose of this protozoal parasite for healthy human volunteers (24), the fact that Tomales Bay is a major shellfish growing region in central California, and the abilities of oysters and other bivalves to concentrate Giardia cysts from the water column (10), we revisited a subset of these original dairies monitored by Lewis et al (16) to (i) identify climatic and on-farm risk factors associated with high concentrations of cysts or high instantaneous loads (cysts/second) of G. duodenalis in storm-based runoff from these high-cattle-use areas and (ii) evaluate the efficacies of selected BMPs to reduce the concentration or instantaneous load of G. duodenalis in storm runoff compared to that in adjacent control sites.…”

Effects of Biosolids and Manure Application on Microbial Water Quality in Rural Areas in the US

“…In May 2000 runoff from a field treated with cattle manure contaminated a groundwater supply with pathogenic bacteria [65,66]. In addition to human pathogenic E. coli and Campylobacter, other pathogens can also be present and survive in livestock manure.…”