Nutrients and Metal Contaminants Status of Urban Stormwater Ponds

ABSTRACT

Stormwater detention ponds are one of the management options designed to reduce pollution of the receiving water bodies by urban runoff. Many such structures are operated in the Greater Toronto Area. A seasonal survey of four stormwater detention ponds was conducted to estimate the inventories of heavy metals and phosphorus in bottom and suspended sediments. The concentrations of heavy metals in suspended and bottom sediments suggest that land use has the most profound impact on the quality of suspended and deposited sediments, with the pond in an industrial/commercial catchment having the highest metals concentrations, followed by ponds located in the residential catchments. The suspended and bottom sediments data suggest that the removal of heavy metals in these reservoirs may not be adequate. Apart from land use, the magnitude of runoff and seasonal conditions impacted the sediment and water quality in these ponds. The deleterious effects of restricted water circulation during the dry summer conditions and under the winter ice cover are apparent from the elevated levels of ammonia-N, sometimes reaching or exceeding the levels recommended by the Canadian Water Quality Guidelines (CCREM 1987) for the protection of aquatic life.

Key Words:

• urban pollution
• urban runoff
• storm water management
• detention ponds
• phosphorus
• metals
• sediments
• suspended sediments