Trace Metals Contamination of Urban Streams and Stormwater Detention Ponds.
In 1991, trace metal levels were monitored over a nine month period in two urban creeks in the Hamilton Harbour watershed and in two urban stormwater detention ponds in Guelph, Ontario. Samples were collected both during dry or non-event periods and immediately after wet weather events. Both water and surficial sediment samples were tested for cadmium, copper, lead, mercury, nickel and zinc. In almost all cases wet weather concentrations of lead, copper and zinc in the water collected from the two urban streams exceeded the Canadian Water Quality Guidelines (CWQGs) for the protection of freshwater aquatic life. While not designed for water quality improvement, both stormwater ponds reduced the levels of metals in discharged water, but in the process trace metals accumulated in sediment to levels above the lowest effect level guideline for the protection and management of aquatic sediment in Ontario, and in the case of zinc above the severe effect level guideline. Although these levels are above guidelines, further investigation is needed to establish a relationship between metal contamination and biological impacts. This is particularly important for ponds intended for the dual purposes of stormwater treatment and as habitat for biota.
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