Abstract:

Stormwater management (SWM) ponds are common approaches employed to replace natural stormwater retention and cycling process that are no present in urban areas with significant areas of impervious surfaces. While initially designed to reduce flooding in downstream receiving waters, SWM ponds are increasingly being relied upon to treat urban runoff removing contaminants that are acquired as precipitation and meltwaters flow across urban surfaces including roads, parking areas, lawns, and parks. Understanding how effective SWM ponds are at reducing contaminants is complicated due to potential daily and seasonal differences in influent quality, seasonal activity of biota involved in contaminant cycling and the frequency and timing of required monitoring. To better understand SWM function we monitored daily influent/effluent flow in two SWM ponds in Waterloo, ON over one-year period, assessed year-round removal efficiency using established guidelines, and evaluated potential ecological impacts of effluent water quality. In the two ponds, effluent concentrations of total phosphorus were above eutrophic concentrations (0.03 mg/l) 10.7 – 40.2% of the time. Chloride concentrations were above chronic exposure values (120 mg/l) between 88- 99.46% of the year and acute concentrations (640 mg/l) 21.59 – 55.1% of year. Chronic elevations of TSS, >5 mg/l above background levels occurred between 65-70% of the time and acute elevations, > 25 mg/l above background levels occurred between 15-25% of the year. DO was below recommended concentrations (5.5 mg/l) between 9-29% of the year. Water quality in and exiting the SWM ponds has the potential to impact aquatic biota and the ecosystem services they provide.