VOLATILIZATION OF MERCURY FROM LAKE SURFACES

Field studies were performed in Canada (at Eagle Lake in north-western Ontario) during July 1986 and subsequently at four oligotrophic forest lakes in south-western Sweden during 1988 and 1989 to determine the extent of mercury volatilization. The Canadian investigations involved simultaneous measurements of total vapour-phase mercury concentrations in air sampled immediately above the water surface and over land nearby. A diurnal cycle was observed for mercury emissions from Eagle Lake, with day-time volatilization rates significantly larger than night-time rates. The Swedish field measurements employed a flux chamber. This device was used to determine the rates at which volatile mercury species were emitted from the lakes. Volatilization occurred from each of the Swedish forest lakes during the warmer seasons of the year (with near-surface water temperatures in the 13-23-degrees-C range). For day-time measurements, volatilization rates were generally 3-10 ng Hg m-2 h-1. Day-time fluxes were, on average, about 2.5-times larger than night-time fluxes. Experiments conducted during the winter season (with water temperatures just above the freezing point) indicated very little, if any, emission of volatile mercury species from the lake surface.