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MODELING MERCURY FLUXES AND CONCENTRATIONS IN A GEORGIA WATERSHED RECEIVING ATMOSPHERIC DEPOSITION LOAD FROM DIRECT AND INDIRECT SOURCES
Citation:
Ambrose Jr., R B., I. X. Tsiros, AND T A. Wool. MODELING MERCURY FLUXES AND CONCENTRATIONS IN A GEORGIA WATERSHED RECEIVING ATMOSPHERIC DEPOSITION LOAD FROM DIRECT AND INDIRECT SOURCES. JOURNAL OF THE AIR & WASTE MANAGEMENT ASSOCIATION 55(5):547-558, (2005).
Impact/Purpose:
To improve the scientific understanding of the linkage between fish methylmercury and ambient mercury in the environment.
To complete a model for transformation and bioaccumulation of mercury than can be linked with models for atmospheric deposition and hydrology to yield a multimedia integrated modeling system capable of quantifying regional exposure to mercury.
To apply state of the art watershed and water body modeling to assess exposures to mercury for impacted aquatic ecosystems.
Description:
This paper presents a modeling analysis of airborne mercury deposited onto the Ochlockonee River watershed located in Georgia, USA. Atmospheric deposition monitoring and source attribution data were used along with simulation models to calculate mercury build-up in the subwatershed soils, its subsequent runoff loading and delivery through the tributaries, and its ultimate fate in the mainstem river. The terrestrial model calculated annual watershed yields for total mercury ranging from 0.7 to 1.1 micrograms/m2. Results suggest that about 2/3 of the atmospherically deposited mercury to the watershed is returned to the atmosphere, 10% is delivered to the river, and the rest is retained in the watershed. A check of the aquatic model results against survey data showed a reasonable agreement. Comparing observed and simulated total and methylmercury concentrations gave RMSE values of 0.26 ng/l and 0.10 ng/l, respectively, in the water column, and 5.9 ng/g and 1.0 ng/g, respectively, in the upper sediment layer. Sensitivity analysis results imply that mercury in the Ochlockonee River is dominated by watershed runoff inputs and not by direct atmospheric deposition, and that methylmercury concentrations in the river are mainly determined by net methylation rates in the watershed, presumably in wetted soils and in the wetlands feeding the river.