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A MODELLING FRAMEWORK FOR MERCURY CYCLING IN LAKE MICHIGAN
Zhang, X. AND K R. Rygwelski. A MODELLING FRAMEWORK FOR MERCURY CYCLING IN LAKE MICHIGAN. Presented at International Association for Great Lakes Research 2000 Conference, Great Lakes, Great Rivers, A Vision for Tomorrow, Cornwall, Ontario, Canada, May 21-26, 2000.
A time-dependent mercury model was developed to describe mercury cycling in Lake Michigan. The model addresses dynamic relationships between net mercury loadings and the resulting concentrations of mercury species in the water and sediment. The simplified predictive modeling framework as formulated based on the current state of knowledge in mercury cycling and some general assumptions detived from lake-specific conditions. The primary focus of the model is the cycling of three mercury groups represented by elemental mercury [Hg(0)], inorganic mercury [Hg(II)], and methyl-mercury [CH3Hg(II)] in the aquatic environment. The transformations among the mercury groups are streamlined with a net mercury methylation/demethylation rate in the model. Model calculations are based on four mass (mole) balance equations describing the cycling of total mercury and the methyl-mercury group among water and sediment compartments. The model contains only a small set of basic and readily available model parameters, and thus requires only minimum calibrations or adjustments of model variables. For demonstration purposes, the model was tested against available data on total mercury, methyl-mercury, and elemental mercury in Lake Michigan. Model results agree well with these data. This whole lake model will be further verified using data from the Lake Michigan Mass Balance Project when all of those data are available.