The effect of drawdown on suspended solids and phosphorus export from Columbia Lake, Waterloo, Canada

Abstract

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 1Ð15 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 (0Ð65 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 8Ð5% of the suspended solids export by mass. A total mass of 18Ð5 t of suspended solids and 62Ð6 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 0Ð5 m below summer levels.

Subsurface Mobilization of Phosphorus in an Agricultural Riparian Zone in Response to Flooding from an Upstream Reservoir

“…A recent study in Texas demonstrated that an upstream impoundment influenced the movement of stream water to the groundwater system in a downstream riparian zone and increased the productivity of riparian vegetation (Duke et al, 2007). The release of water from reservoirs in autumn promotes the release of sediments and associated nutrients and increases the nutrient flux to downstream environments (Shantz et al, 2004). While previous studies of the impacts of reservoir release have primarily focused on in-channel processes (Petts, 1984;Shantz et al, 2004), much less attention has been given to how the biogeochemical function of adjacent riparian areas in downstream areas may be affected during flood events caused by reservoir release.…”

“…The release of water from reservoirs in autumn promotes the release of sediments and associated nutrients and increases the nutrient flux to downstream environments (Shantz et al, 2004). While previous studies of the impacts of reservoir release have primarily focused on in-channel processes (Petts, 1984;Shantz et al, 2004), much less attention has been given to how the biogeochemical function of adjacent riparian areas in downstream areas may be affected during flood events caused by reservoir release. Elevated P fluxes from streams to riparian zones during storm-based flooding have been observed (Walling et al, 2000;Owens and Walling, 2002).…”

Sedimentary phosphorus in a cascade of five reservoirs (Lozoya River, Central Spain)

“…The amount of dissolved phosphate released into the water depends on many factors, including interactions with calcium (Ca), organic matter, iron, and humic materials, which play a significant role depending on the catchment geology and trophic status (Andersen andJensen 1992, Gatcher andMeyer 1993;Nurnberg 1998;Wang et al 2004). Further, resuspension of particles determine the increased amount of phosphorus released to the water in dissolved and particulate forms (Shantz et al 2004;Welch and Cooke 2005). The release of phosphorus from sediments (i.e., internal loading) may further facilitate cyanobacterial blooms, as reported in several water bodies (Hyenstrand et al 1998;Johnston and Jacoby 2003;Wang et al 2005).…”

Ecological impacts of winter water level drawdowns on lake littoral zones: a review

“…Thus, a relatively low rate of water drawdown and refill may enhance erosion of shallow littoral areas by increasing the exposure time to wind/wave energy (Lorang et al 1993). Shallow, gently sloping lakes show a less distinct sedimentation response to drawdowns (Hellsten 1997) because fine sediment is more susceptible to entrainment in these lakes (Havens et al 2004;Shantz et al 2004).…”