Gaseous mercury emissions from natural sources in Canadian landscapes

Field measurements of mercury air-surface exchange from natural settings were made in various Canadian landscapes. Soil and water samples were analyzed for mercury concentrations, and air-surface exchange fluxes from these substrates were determined using dynamic chamber, micrometeorological, or modeling methods. Environmental variables, including air and soil/water temperature, solar radiation, humidity, and wind speed, were monitored concurrently with the air-surface exchange to better understand the processes affecting the environmental cycling of mercury. Average mercury fluxes from aquatic landscapes ranged from 0.0 to 5.0 ng m^-2 h^-1 with total mercury concentration in water ranging from 0.3 to 6.5 ng L^-1. A significant correlation (R² = 0.47) was found between gaseous Hg fluxes and total Hg concentration in water. Mean gaseous Hg fluxes from forest soils varied from -0.4 to 2.2 ng m^-2 h^-1, while those from agricultural fields ranged from 1.1 to 2.9 ng m^-2 h^-1. Non-mineralized bedrock, sand, and fill sites yielded fluxes ranging from -0.03 to 5.9 ng m^-2 h^-1. Mean fluxes from mercuriferous geological substrates at various locations were large compared to non-mercuriferous sites, ranging from 9.1 to 1760 ng m^-2 h^-1, and represent natural emissions. The corresponding total mercury substrate concentrations ranged from 0.360 to 180 ppm. A significant correlation (R² = 0.66) was found between Hg fluxes and total Hg concentrations in mineralized and non-mineralized substrates. These gaseous Hg flux measurements represent a significant contribution to understanding natural mercury cycling, but there are still insufficient data and knowledge of processes to properly scale up fluxes from natural sources in Canada.