Evaluation of aquatic vegetation management techniques in stormwater retention basins

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Wardrop, David A.
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The City of Winnipeg Water and Waste Department presently operates and maintains 70 Stormwater Retention Basins (SRB's) within its boundaries. Limitations on the number of harvestable basins exist due to time, availability of equipment, site conditions at some stormwater retention basins, and budget. These problems, in addition to the rapid proliferation of weed and algae concentrations observed subsequent to harvesting, resulted in questions with respect to the impact mechanical harvesting has upon chlorophyll a concentrations in SRB's. Water quality analysis indicated that subsequent to harvesting activities, no reduction in chlorophyll a concentration was observed in any of the test basins, despite the removal of aquatic vegetation during harvesting. Plausible explanations for the increase in chlorophyll a following harvesting were discussed and investigated. Historically, harvesting activities had been supported with the application of copper sulphate and simazine based sterilents until the recent ban of these products from SRB application necessitated research into alternatives. Review of alternative emerging weed and algae control methods indicated that the most promising methods available to supplement o replace the aquatic weed harvesting program included sterilized grass carp and the use of the commercially available herbicides Reglone A and Karmex DF. Investigation into the effectiveness of the herbicides Karmex DF and Reglone A indicated that both provided promise as competitive means for weed and algae control, and either could prove to be an important supplement to, or a replacement for, conventional harvesting practices. (Abstract shortened by UMI.)