AWWA WQTC63993

The occurrence of various species and genotypes of Cryptosporidium in raw water represent both cumulative and point source impacts present within a watershed. This is further complicated by physical and hydro-geographical characteristics of the waterway as well as the topography and land use patterns of the catchment area. Successful environmental risk assessment strategies need not only examine faecal impacts, but must also incorporate comprehensive land use analysis. A study was carried out in the Oldman River in Alberta, Canada where Cryptosporidium species and genotypes were monitored at three sites on a monthly basis for 1 year. Host specificity of Cryptosporidium and land use patterns were combined to track the source of faecal contamination. The number of oocysts detected using US Environmental Protection Agency Method 1623 ranged from non-detectable to 1.9 oocysts per liter. The site furthest upstream had the fewest occurrences of Cryptosporidium oocysts with three sampling periods positive at a rate of 0.02 oocysts per liter. Molecular forensic profiling of Cryptosporidium oocysts recovered from microscope slides of the two downstream sites indicated that C. andersoni was the predominant species in the Oldman River. Source tracking methods along with land use analysis indicate cattle are likely to be the largest contributor of Cryptosporidium to the river. C. baileyi occurred at both downstream sites in late summer and the fall, W13 genotype was detected at the middle site over a period of 3 months, and genotype W16 was detected only once at the most downstream site. Birds, skunks, raccoons and muskrats were suspected to be the contributors of the sporadic occurrences of these species and genotypes. The Cryptosporidium species and genotypes present in the Oldman River pose little risk to human health. The study demonstrates the value of an integrated approach to risk assessment by combining occurrence monitoring, species identification and land use into a more robust tool for source tracking faecal contamination. Includes 20 references, table, figures.