Variation in Water Quality of a Stormwater Pond from Diurnal Thermal Stratification

The city of Calgary, Canada, has considered reusing stormwater from detention ponds for the irrigation of public lands. The diurnal variability in the water quality of these ponds was studied to ensure public safety. Field observations of diurnal thermal stratification and diurnal variation in water quality were conducted in a stormwater pond during the 2007 irrigation season normally from late June to September. Diurnal thermal stratification occurred in the upper water column, from the surface to approximately 1.2 m in depth. Diurnal variations in microorganisms involved high concentrations during the day and low concentrations at night. Increases in physicochemical water quality parameters at night were observed at the bottom of the water column, at a depth of 1.0 m. Observations suggest that the effects of diurnal thermal stratification alter pond hydrodynamics, and thus, alter the diurnal variation of water quality in turn.