Pathogen and indicator variability in a heavily impacted watershed.

Water samples were collected from 36 locations within the Grand River Watershed, in Southwestern Ontario, Canada from July 2002 to December 2003 and were analyzed for total coliforms, fecal coliforms, Escherichia coli, Escherichia coli O157:H7, and thermophilic Campylobacter spp. A subset of samples was also analyzed for Cryptosporidium spp., Giardia spp., culturable human enteric viruses, and Clostridium perfringens. Storm and snowmelt events were sampled at two locations including a drinking water intake. For the majority of the events, the Spearman rank correlation test showed a positive correlation between E. coli levels and turbidity. Peaks in pathogen numbers frequently preceded the peaks in numbers of indicator organisms and turbidity. Pathogen levels sometimes decreased to undetectable levels during an event. As pathogen peaks did not correspond to turbidity and indicator peaks, the correlations were weak. Weak correlations may be the result of differences in the sources of the pathogens, rather than differences in pathogen movement through the environment. Results from this investigation have implications for planning monitoring programs for water quality and for the development of pathogen fate and transport models to be used for source water risk assessment.

Assessing levels of pathogenic contamination in a heavily impacted river used as a drinking-water source.

This paper describes initial results from a research program that aims to gain greater understanding of sources of pathogens and the environmental factors that influence their survival and transport in watersheds. An additional goal is to enhance the ability to predict potential levels of pathogenic microorganisms arriving at drinking-water treatment plant intakes. The objectives will be supported by an intensive monitoring program examining the temporal and spatial variability of pathogens in a test watershed (the Grand River Watershed, Ontario). As many as 500,000 people potentially receive at least part of their drinking water from the Grand River. The watershed has significant urban and agricultural use. Sampling for total coliforms, fecal coliforms, Escherichia coli, Escherichia coli O157:H7, and Campylobacter spp. began in July 2002. Although presumptive tests were occasionally positive, no Escherichia coli O157:H7 or Campylobacter spp. were confirmed to be present in water samples taken. Escherichia coli O157:H7 was, however, detected in a tributary of the Grand River during an initial investigation. Preliminary results did not show any statistically significant differences between coliform concentrations upstream and downstream of wastewater treatment plants. Data suggest that nonpoint sources may have a greater effect on routine stream coliform concentrations.