Fate and transport of ambient and amended mercury in a stratified temperate lake

The specific processes and pathways controlling the speciation and subsequent fate, transport, and reactivity of ambient and amended Hg and MeHg were investigated in an experimental lake and its terrestrial catchment. The research was conducted at Lake 658 within the Experimental Lakes Area (ELA) in Canada as part of the project entitled "Mercury Experiment To Assess Atmospheric Loading in Canada and the United States" (METAALICUS) where amended isotopic Hg was used to explore the relationships between atmospheric loading and bioaccumulation in freshwater biota. Lake 658, an 8 hectare first-order boreal lake, was dosed bi-monthly with stable 202Hg nine times during each summer of 2001--2006 at a loading 4 to 5 times the annual wet deposition (∼20 ug/m2/year). In addition, 200Hg and 198Hg were applied annually to the 42 hectare upland and 2 hectare wetland portions of the lacustrine watershed, respectively.{09} The use of stable isotopes and inductively couple plasma - mass spectrometry (ICP-MS) allowed for the analytical discrimination of amended Hg from the native pool of Hg.; The spatial and temporal changes in ambient and amended Hg and MeHg speciation in the aqueous and particulate phases were evaluated using water column profiles, sediment traps, and a series of systematic experiments to evaluate processing controlling Hg and MeHg. The spatial and temporal particle partitioning relationships for ambient and amended Hg and MeHg were statistically examined across physical and chemical gradients in the water column. The particulate phases controlling the transport and speciation of ambient and amended Hg and MeHg within the hypolimnion were examined using sequential extraction and batch reactor experiments. The role of dissolved organic matter (DOM) in the speciation and transport of Hg and MeHg in the water column and terrestrial catchment was examined using diethylaminoethyl resin. The kinetics of amended Hg(II) particle partitioning in the water column and the role of Hg loading on partitioning kinetics and equilibrium was examined using a 201Hg(II) isotopic tracer. Although the behaviors of ambient and amended Hg and MeHg were similar, significant temporal and spatial differences were observed in the physical and chemical speciation.