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The Effectiveness of stormwater ponds in contaminant removal from urban stormwater runoff in the Lower Fraser Valley, BC Brydon, Julia

Abstract

As urbanization progresses rapidly throughout the Lower Fraser Valley (LFV) and many other areas in Canada, contaminants associated with urban land uses are found in elevated concentrations in urban waterways. One of the most common mitigation methods is the construction of stormwater ponds, which provide detention for volume control and remediation for water quality improvement. The aim of this research is to investigate the quality of the stormwater entering five ponds in urban areas in the LFV and the effectiveness of trace metal and phosphorus removal in these ponds during the wet and dry seasons. Both water and sediment from the inlets and outlets of the ponds are analysed. A new technique of Diffusive Gradient in Thin Films (DGT) was employed to capture available metals over time and determine the accumulation of bioavailable metals during different storm events. The results show that an average of 26% (range 0 - 60%) of the samples of inlet water from the ponds exceeded the guideline for zinc of the Canadian Environmental Quality Guidelines for Freshwater Aquatic Life. Copper and zinc concentrations found in the sediment at the inlets of all ponds exceeded the Probable Effects Level. The concentration of these metals is correlated to traffic volumes and percent impervious cover in the catchments. Zinc concentrations are reduced through the ponds by up to 41% in the water, 65% in the sediments and 78% in bioavailability. Most ponds were not effective in retaining aluminum, iron or manganese in the water and sediments. However, the bioavailable form of these metals is reduced particularly during the wet period by an average of 29% (range -155% to 81%). The extent of vegetation in the ponds had the strongest overall correlation to contaminant reduction in water, sediment and bioavailability, while surface area and volume were correlated to only reductions in manganese. In conclusion, the most effective designs incorporate a combination of vegetation in the pond, a sufficient flow of water throughout the wet season, and a design that aids consistent sedimentation of coarse particles through the pond, while impeding the flow of finer clay particles to allow for remediation.

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