Transient storage and release of sediment and phosphorus in a small urban impoundment

摘要

A mass balance approach was used to quantify concentrations and loads of suspended solids and phosphorus (P) at the inflow and outflow of Laurel Pond, a small river impoundment in an urbanized watershed in Waterloo, Ontario, Canada, over a range of hydrological conditions. During baseflow and higher magnitude flow conditions, Laurel Pond was a sink for both sediment and P. However, 8.4 t of sediment and 8.6 kg of P were released from Laurel Pond during drawdown. Concentrations of sediment and P were positively correlated but inversely related to pond depth. A threshold water level was observed in the pond, below which the majority of sediment and P were released. During the Laurel Pond drawdown, 94% of suspended solids and 100% of TP measurements at the pond outflow exceeded Ontario Provincial Water Quality Objectives of 25 mg L~(-1) and 30 μg L~(-1), respectively.