Winter operation of an on-stream stormwater management pond.

The winter operation of an on-stream stormwater management pond in Kingston, Canada is characterised. The pond froze over in late November. Ice thickness varied from 0.2 to 0.5 m, and initially, was well described by Stefan's formula. The measured and modelled velocity field indicated a fast flow region, a small dead zone and a large recirculating zone. During a snowmelt event, near-bottom velocities reached 0.05 m x s(-1), but were not sufficient to scour the bottom sediment. Pond water temperature increased with depth, from 0.5 degrees C to 3.5 degrees C. The dissolved oxygen (DO) levels observed in the pond (6-13 mg x L(-1)) indicated stable aerobic conditions at the sediment-water interface. In one brief episode, DO fell to zero after a long cold spell. Reduction in DO readings from inlet to outlet indicated an oxygen consumption of about 1.7 kg x day(-1). pH ranged from 7.1 to 8.9. Conductivity readings indicated large quantities of total dissolved solids, representing mostly chloride from de-icing agents. During baseflow, conductivity increased with depth (total dissolved solids concentrations up to 1,200 mg x L(-1) near the bottom), indicating density stratification. Average trace metal concentrations were mostly below detection limits.