Spatial and Temporal Variations of Fecal Indicator Bacteria in Stormwater Ponds in Calgary, Alberta

Abstract

Urban stormwater runoff is acknowledged to be the primary source of microbial contamination in stormwater ponds. The microbial quality would constrain the reuse of stormwater in these bodies (e.g., for irrigation) to reduce potable water demands. In the context of microbial quality, less is known about its spatial distribution and temporal variation, and their influential factors. In this study, Escherichia-coli (E.coli) and fecal coliform (FC), which are commonly used Fecal Indicator Bacteria (FIB), were monitored and the microbial source tracking was conducted in the Inverness, McCall Lake, and Country Hills stormwater ponds situated in the City of Calgary, Alberta. These ponds have been considered as the potential sites for stormwater reuse. The statistical analysis was conducted to analyze the monitoring data aiming to investigate the spatial and temporal variations of the microbial quality. The results showed that the FIBs were heterogeneously distributed in each pond. Overall, the FIB concentrations at the sampling locations in the vicinity of outfalls draining into the ponds were significantly or relatively higher than those in the vicinity of inlets draining out of the ponds. The results also implied that stormwater drained from the subcatchments with a higher percentage of commercial land use was more contaminated than those with primary residential land use. Rain events were found to elevate the FIB concentrations in general, while the antecedent rainfall was also detected to affect the FIB concentrations at several sampling sites. Whereas increased levels of FIB concentrations were also observed during dry periods or following very light rainfalls, especially in McCall Lake Stormwater Pond. This might be ascribed to the human sewage contamination, as it was found to be another main source of microbial pollution, especially in McCall Lake Stormwater Pond, followed by seagull feces in the microbial source tracking. Moreover, the temporal variations of FIB concentrations were observed from the Inverness Stormwater Pond, whose land use was largely changed due to increased residential development during the monitoring period. The results, however, suggested that the temporal variation might be more associated with the meteorological conditions (rainfall and/or temperature) than the residential development.