The effect of drawdown on suspended solids and phosphorus export from Columbia Lake, Waterloo, Canada
✍ Scribed by Mike Shantz; Elizabeth Dowsett; Emma Canham; Guillaume Tavernier; Mike Stone; Jonathan Price
- Publisher
- John Wiley and Sons
- Year
- 2004
- Tongue
- English
- Weight
- 494 KB
- Volume
- 18
- Category
- Article
- ISSN
- 0885-6087
- DOI
- 10.1002/hyp.1300
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✦ Synopsis
Abstract
This study examines the effect of drawdown on the timing and magnitude of suspended solids and associated phosphorus export from a 12 ha reservoir located in an urbanized watershed in southern Ontario, Canada. Water level in Columbia Lake was lowered by 1·15 m over a 2‐week period in November 2001. The total phosphorus (TP) concentrations ranged from 63 to 486 µg L^−1^ in Columbia Lake and 71 to 373 µg L^−1^ at its outflow. All samples exceeded the Provincial Water Quality Objective of 30 µg TP L^−1^. Outflow concentrations of suspended solids and TP increased significantly with decreasing lake level and were attributed to the resuspension of cohesive bottom sediments that occurred at a critical threshold lake level (0·65 m below summer level). Suspended solids at the outflow consisted of flocculated cohesive materials with a median diameter (D~50~) of c. 5 µm. Particulate organic carbon accounted for 8·5% of the suspended solids export by mass. A total mass of 18·5 t of suspended solids and 62·6 kg TP was exported from Columbia Lake, which represents a significant pulse of sediment‐associated P to downstream environments each autumn during drawdown. The downstream impacts of this release can be minimized if the water level in Columbia Lake is lowered no more than 0·5 m below summer levels. Copyright © 2004 John Wiley & Sons, Ltd.