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Mercury mass balance in Lake Michigan--the knowns and unknowns
Citation:
Rygwelski, K., X. Zhang, M. Rowe, R. Rossmann, AND R. Kreis. Mercury mass balance in Lake Michigan--the knowns and unknowns. Presented at EPA Great Lakes National Program Office Workshop: Mercury Science in the Great Lakes.
Impact/Purpose:
LM2-Mercury, a mercury mass balance model, was developed to simulate and evaluate the transport, fate, and biogeochemical transformations of mercury in Lake Michigan. The model simulates total suspended solids (TSS), disolved organic carbon (DOC), and total, elemental, divalent, and methyl mercury as state variables. The transport and fate of mercury are linked to the movement of water, TSS, and DOC in the model. Simplified speciation processes among the mercury species including reduction of divalent mercury, methylation, and demethylation are incorporated in the model. LM2-Mercury is the only comprehensive, multi-compartment model to date that is capable of simultaneously simulating the dynamics of suspended solids, total mercury, and the three most important mercury species in Lake Michigan. Using the model, a mass budget assessment of mercury cycling in the lake was conducted. The results of the assessment indicate that the atmospheric loading, including wet and dry deposition and absorption of reactive gaseous mercury (RGM), was dominate direct external contributor of total mercury to Lake Michigan, while water-sediment interaction (settling and resuspension) and air-water exchange were the key processes controlling the fate of total mercury in the lake. The dominate internal sources for elemental and methyl mercury in the water column were from divalent mercury reduction and divalent mercury methylation, respectively. The greatest loss of methyl mercury from the surficial sediments was due to demethylation. Using this calibrated model, forecasts of mercury concentrations in lake water were made and these were compared to fish consumption advisories. The local and global inputs of mercury were evaluated in the model forecast scenarios. Modeling knowns and unknowns will be discussed.
Description:
LM2-Mercury, a mercury mass balance model, was developed to simulate and evaluate the transport, fate, and biogeochemical transformations of mercury in Lake Michigan. The model simulates total suspended solids (TSS), disolved organic carbon (DOC), and total, elemental, divalent, and methyl mercury as state variables. The transport and fate of mercury are linked to the movement of water, TSS, and DOC in the model. Simplified speciation processes among the mercury species including reduction of divalent mercury, methylation, and demethylation are incorporated in the model. LM2-Mercury is the only comprehensive, multi-compartment model to date that is capable of simultaneously simulating the dynamics of suspended solids, total mercury, and the three most important mercury species in Lake Michigan. Using the model, a mass budget assessment of mercury cycling in the lake was conducted. The results of the assessment indicate that the atmospheric loading, including wet and dry deposition and absorption of reactive gaseous mercury (RGM), was dominate direct external contributor of total mercury to Lake Michigan, while water-sediment interaction (settling and resuspension) and air-water exchange were the key processes controlling the fate of total mercury in the lake. The dominate internal sources for elemental and methyl mercury in the water column were from divalent mercury reduction and divalent mercury methylation, respectively. The greatest loss of methyl mercury from the surficial sediments was due to demethylation. Using this calibrated model, forecasts of mercury concentrations in lake water were made and these were compared to fish consumption advisories. The local and global inputs of mercury were evaluated in the model forecast scenarios. Modeling knowns and unknowns will be discussed.