Air-water gas exchange of chlorinated pesticides in four lakes spanning a 1,205 meter elevation range in the Canadian Rocky Mountains

Concentrations of selected persistent organic pollutants (POPs) in air and water were measured from four lakes that transect the Canadian Rocky Mountains. These data were used in combination with wind velocity and temperature-adjusted Henry's law constants to estimate the direction and magnitude of chemical exchange across the air-water interface of these lakes. Bow Lake (1,975 in above sea level [masl]) was studied during the Summers of 1998 through 2000; Donald (770 masl) was studied during the summer of 1999; Dixon Dam Lake (946 masl]) and Kananaskis Lake (1,667 masl) were studied during the summer of 2000. Hexachlorobenzene (HCB) and dieldrin volatilized from Bow Lake in spring and summer of 1998 to 2000 at a rate of 0.92 +/- 1.1 and 0.55 +/- 0.37 ng m(-2) d(-1), respectively. The alpha-endosulfan deposited to Bow Lake at a rate of 3.4 +/- 2.2 ng m(-2) d(-1). Direction of gas exchange for gamma-hexachlorocyclohexane (-gamma-HCH) changed from net deposition in 1998 to net volatilization in 1999, partly because of a surge in -gamma-HCH concentrations in the water at Bow Lake in 1999. Average -gamma-HCH concentrations in air declined steadily over the three-year period, from 0.021 ng m(-3) in 1998, to 0.0023 ng m(-3) in 2000, and to volatilization in 1999 and 2000. Neither the concentrations of organochlorine compounds (OCs) in air and water, nor the direction and rate of air-water gas exchange correlate with temperature or elevation. In general, losses of pesticides by outflow were greater than the amount exchanged across the air-water interface in these lakes.