A hypolimnetic mass balance of mercury from a dimictic lake: Results from the METAALICUS project

Our ability to determine the fate and transport of newly deposited mercury, from that of historically deposited mercury, was recently demonstrated by the Mercury Experiment To Assess Atmospheric Loading In Canada and the United States (METAALICUS). The METAALICUS project is a whole-watershed amendment study where different stable isotopes of mercury were applied to three watershed compartments totaling similar to53 Hectares: the upland, the wetland, and the surface of a dimictic lake in northwestern Ontario, Canada. Each compartment received approximately 5 times the annual background atmospheric deposition for the region. In the lake, the spike was divided into 9 bi-weekly injections administered over several hours through the wash of a trolling motor while circling the lake. The spike was added at dusk to limit photo reduction and evasion of elemental mercury. Results from two years of data show that new mercury is extremely particle reactive. Implications for the availability of newly deposited mercury for methylation, and a well-constrained mass balance of the hypolimnetic mercury cycle, will be presented.