Publication Date:
2004-04-15
Description:
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 (D50) 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. © 2004 John Wiley and Sons, Ltd.
Print ISSN:
0885-6087
Electronic ISSN:
1099-1085
Topics:
Architecture, Civil Engineering, Surveying
,
Geography
Permalink