Prioritizing watershed pathogen research

105

Processes by which fecal bacteria enter overland flow and their transportation state to surface waters are poorly understood, making the effectiveness of measures designed to intercept this pathway, such as vegetated buffer strips, difficult to predict. Freshly made and aged (up to 30 days) cowpats were exposed to simulated rainfall, and samples of the cowpat material and runoff were collected. Escherichia coli in the runoff samples were separated into attached (to particles) and unattached fractions, and the unattached fraction was analyzed to determine if the cells were clumped. Within cowpats, E. coli grew for 6 to 14 days, rather than following a typical logarithmic die-off curve. E. coli numbers in the runoff correlated with numbers inside the cowpat. Most of the E. coli organisms eroded from the cowpats were transported as single cells, and only a small percentage (about 8%) attached to particles. The erosion of E. coli from cowpats and the state in which the cells were transported did not vary with time within a single rainfall event or over time as the cowpats aged and dried out. These findings indicate that cowpats can remain a significant source of E. coli in overland flow for more than 30 days. As well, most of the E. coli organisms eroded from cowpats will occur as readily transportable single cells.

mentioning

confidence: 99%

Erosion and Subsequent Transport State of Escherichia coli from Cowpats

Muirhead

Collins

Bremer

2005

105

“…There have been few attempts to quantify the relationship between pathogen dispersion and transport, rainfall, and surface water pathogen loads. Recent reviews (18,20) identified that artificial buffer strips can be highly effective at retarding oocyst transport (7), with vegetated setbacks as little as 1 m being considered sufficient in one watershed. Models to estimate sediment and nutrient export from land and design criteria to predict the retardation of these pollutants by buffer strips (41) are available.…”

mentioning

confidence: 99%

Dispersion and Transport of Cryptosporidium Oocysts from Fecal Pats under Simulated Rainfall Events

Davies

Ferguson

Kaucner

et al. 2004

Self Cite

The dispersion and initial transport of Cryptosporidium oocysts from fecal pats were investigated during artificial rainfall events on intact soil blocks (1,500 by 900 by 300 mm). Rainfall events of 55 mm h ؊1 for 30 min and 25 mm h ؊1 for 180 min were applied to soil plots with artificial fecal pats seeded with approximately 10 7 oocysts. The soil plots were divided in two, with one side devoid of vegetation and the other left with natural vegetation cover. Each combination of event intensity and duration, vegetation status, and degree of slope (5°a nd 10°) was evaluated twice. Generally, a fivefold increase (P < 0.05) in runoff volume was generated on bare soil compared to vegetated soil, and significantly more infiltration, although highly variable, occurred through the vegetated soil blocks (P < 0.05). Runoff volume, event conditions (intensity and duration), vegetation status, degree of slope, and their interactions significantly affected the load of oocysts in the runoff. Surface runoff transported from 10 0.2 oocysts from vegetated loam soil (25-mm h ؊1 , 180-min event on 10°slope) to up to 10 4.5 oocysts from unvegetated soil (55-mm h ؊1 , 30-min event on 10°slope) over a 1-m distance. Surface soil samples downhill of the fecal pat contained significantly higher concentrations of oocysts on devegetated blocks than on vegetated blocks. Based on these results, there is a need to account for surface soil vegetation coverage as well as slope and rainfall runoff in future assessments of Cryptosporidium transport and when managing pathogen loads from stock grazing near streams within drinking water watersheds.

“…Oocysts present in animal fecal deposits on land are clearly responsible for many event-related increases in the concentrations of in-stream pathogens in watersheds (3,8). However, there are significant knowledge gaps regarding the mechanisms and magnitude of pathogen transport and the effects of environmental factors on oocyst inactivation (7). In particular, there have been few attempts to predict the fate of oocysts deposited on land by using quantifiable parameters.…”

mentioning

confidence: 99%

Recovery and Enumeration of Cryptosporidium parvum from Animal Fecal Matrices

Davies

Kaucner

Deere

et al. 2003

Self Cite

Accurate quantification of Cryptosporidium parvum oocysts in animal fecal deposits on land is an essential starting point for estimating watershed C. parvum loads. Due to the general poor performance and variable recovery efficiency of existing enumeration methods, protocols were devised based on initial dispersion of oocysts from feces by vortexing in 2 mM tetrasodium pyrophosphate, followed by immunomagnetic separation. The protocols were validated by using an internal control seed preparation to determine the levels of oocyst recovery for a range of fecal types. The levels of recovery of 10 2 oocysts from cattle feces (0.5 g of processed feces) ranged from 31 to 46%, and the levels of recovery from sheep feces (0.25 g of processed feces) ranged from 21% to 35%. The within-sample coefficients of variation for the percentages of recovery from five replicates ranged from 10 to 50%. The ranges for levels of recovery of oocysts from cattle, kangaroo, pig, and sheep feces (juveniles and adults) collected in a subsequent watershed animal fecal survey were far wider than the ranges predicted by the validation data. Based on the use of an internal control added to each fecal sample, the levels of recovery ranged from 0 to 83% for cattle, from 4 to 62% for sheep, from 1 to 42% for pigs, and from 40 to 73% for kangaroos. Given the variation in the levels of recovery of oocysts from different fecal matrices, it is recommended that an internal control be added to at least one replicate of every fecal sample analyzed to determine the percentage of recovery. Depending on the animal type and based on the lowest approximate percentages of recovery, between 10 and 100 oocysts g of feces ؊1 must be present to be detected.The protozoan parasite Cryptosporidium parvum is a major cause of waterborne diarrheal illness in human and animal populations. The transmissive form of this organism, the oocyst, frequently finds its way into surface waters, either directly through sewage discharge or indirectly in runoff from land grazed by livestock or wildlife. Oocysts present in animal fecal deposits on land are clearly responsible for many event-related increases in the concentrations of in-stream pathogens in watersheds (3, 8). However, there are significant knowledge gaps regarding the mechanisms and magnitude of pathogen transport and the effects of environmental factors on oocyst inactivation (7). In particular, there have been few attempts to predict the fate of oocysts deposited on land by using quantifiable parameters. The responsible authorities are advocating adequate watershed management as a fundamental requirement for reducing pathogen risks to drinking water quality, and the United States Environmental Protection Agency is seeking estimates of total maximum daily loads for watershed pathogens (18). The quantification of transport mechanisms and environmental inactivation for key pathogens should enable models to be constructed that can be used to predict source water quality in order to better manage the factors that govern p...