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Global and regional contributions to total mercury concentrations in Lake Michigan water
Citation:
Zhang, X., K. Rygwelski, M. Rowe, R. Rossmann, AND R. Kreis. Global and regional contributions to total mercury concentrations in Lake Michigan water. JOURNAL OF GREAT LAKES RESEARCH. International Association for Great Lakes Research, Ann Arbor, MI, 42(1):62-69, (2016).
Impact/Purpose:
LM2 Mercury, a mass balance model, was developed to investigate and evaluate the transport, and fate to forecast mercury concentrations in Lake Michigan; and to provide insights into long-term responses of the lake to various mercury management loading scenarios. The long-term responses included predictions of mercury concentrations in water and the impact on fish consumption advisories for six year old Lake Trout. The model simulates total mercury and its interaction with total suspendable and resuspendable solids and dissolved organic carbon. The model was designed to have enough sophistication in model conceptualization to capture key processes while maintaining simplicity of speciation processes. The model was thoroughly calibrated to intensive and comprehensive field data collected during 1994 and 1995. In addition, a mercury model hind-cast was conducted and corroborated well with sediment data. These results were published in the Journal of Great Lakes Research in 2014. In this new paper, the model forecasts appear to be comparable to post-audit mercury concentration measurements in water for 2005 and 2010. The constant condition scenario suggests mercury concentrations in the water are near steady state. Model simulations of likely trend scenarios suggest that mercury will continue to decrease in the lake; however, for both high global input and low global input estimations, consumption of adult six year old lake trout will probably continue to be restricted. This work supports the Clean Water Act, Clean Air Act, Critical Programs Act (Lake Michigan LaMP), Great Lakes Legacy Act, Binational Toxics Strategy, and the US-Canada Great Lakes Water Quality Agreement.
Description:
A calibrated mercury component mass balance model, LM2-Mercury, was applied to Lake Michigan to predict mercury concentrations in the lake under different mercury loadings, mercury air concentrations, and management scenarios. Although post-audit data are few, model predictions (volume-weighted, lakewide average total mercury concentrations) appear to be comparable to the available post-audit measurements from 2005 and 2010. The constant condition scenario shows that total mercury concentrations in the lake are near steady-state. The model was used to investigate the relative importance of two very different global versus regional impacts on total mercury concentrations in Lake Michigan. The results of this modeling exercise suggest that mercury input to the lake from global sources could contribute between 30% and 70% of total mercury water concentrations in Lake Michigan. Also, the results from the likely scenarios modeled, based on both high and low global contribution estimates and information on mercury emission trends from current observations and the literature, indicate that mercury concentration in Lake Michigan will continue to decrease; however, the mercury concentrations at the end of model simulations (year 2055) for both likely scenarios will still be expected to exceed the U.S. EPA guidelines for unrestricted fish consumption.
