Abstract
Poor freshwater beach quality, measured by Escherichia coli (E. coli) levels, poses a risk of recreational water illness. This study linked environmental data to E. coli geometric means collected at 18 beaches in Toronto (2008–2019) and the Niagara Region (2011–2019) to examine the environmental predictors of E. coli. We developed region-specific models using mixed effects models to examine E. coli as a continuous variable and recommended thresholds of E. coli concentration (100 CFU/100 mL and 200 CFU/100 mL). Substantial clustering of E. coli values at the beach level was observed in Toronto, while minimal clustering was seen in Niagara, suggesting an important beach-specific effect in Toronto beaches. Air temperature and turbidity (measured directly or visually observed) were positively associated with E. coli in all models in both regions. In Toronto, waterfowl counts, rainfall, stream discharge and water temperature were positively associated with E. coli levels, while solar irradiance and water level were negatively associated. In Niagara, wave height and water level had a positive association with E. coli, while rainfall was negatively associated. The differences in regional models suggest the importance of a region-specific approach to addressing beach water quality. The results can guide beach monitoring and management practices, including predictive modelling.
Highlights
The concentration of Escherichia coli (E. coli) is used as an indicator of recent fecal pollution and signifies risks of recreational water illness in freshwater beaches [1]
We aim to contribute to this research by examining recreational water quality in these two Southern Ontario regions to identify the environmental predictors associated with E. coli concentration at
We examine the beach water quality in 18 beaches located in two regions in Southern
Summary
The concentration of Escherichia coli (E. coli) is used as an indicator of recent fecal pollution and signifies risks of recreational water illness in freshwater beaches [1]. Municipal beach monitoring programs routinely collect water samples to determine whether bacterial concentrations exceed guideline thresholds. Canadian guidelines implemented in 2012 recommend an E. coli geometric mean concentration of less than 200 colony-forming units (CFU)/100 mL averaged from five samples, or less than 400 CFU/100 mL for a single sample, to provide an acceptable risks of illness [2]. Prior to these 2012 guidelines, recreational water quality guidelines recommended a threshold of 100 CFU/100 mL. A limitation of most beach water monitoring programs is the application of a probabilistic approach, where water quality postings are based on the previous day’s testing results due to laboratory processing time
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