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MODELING MERCURY FATE IN SEVEN GEORGIA WATERSHEDS
Ambrose Jr., R B. AND T. A. Wool. MODELING MERCURY FATE IN SEVEN GEORGIA WATERSHEDS. Presented at Workshop on the fate, transport, and transformation of mercury in aquatic and terrestrial environments, West Palm Beach, FL, May 8-10, 2001.
Develop, test, and refine models to evaluate sub-basins to determine whether local water quality problems due to excessive nutrient loading exist, and if so, to characterize them and determine their relationships to nutrient loading. Develop models to simulate overland flow and non-point source pollutant loads to track and assess nutrient loadings across watersheds and provide approaches for estimating nutrient budgets within sub-basins and for predicting changes in nutrient budgets in response to changes in watershed activities/land use/land cover. Demonstrate the application of the recommended approach/models for predicting changes in nutrient budgets in response to changes in proposed watershed activities/land use/land cover, resulting in specific recommendations for reducing the nutrient loads to a basin. For coherence, cooperation, and economics, these models will be housed in a unified, consistent, computational environment for environmental analyses that allows teaching (i.e., technology transfer) to multiple users (users concentrate on problem, not model input/output); that appeals to multi-disciplinary groups for distribution and use as a consistent assessment methodology (includes models, tools, modular design and facilitated updates of science/engineering); that includes resident visualization, animation tools, documentation and tutorials on-line, hooks to GIS and environmental databases; and is executable on UNIX, personal computers, and HPC resources.
Objective # 2.2 Conserve and enhance nation's waters: By 2005, conserve and enhance the ecological health of the nation's (state, interstate, and tribal) waters and aquatic ecosystems-rivers and streams, lakes, wetlands, estuaries, coastal areas, oceans, and groundwater-so that 75% of waters will support healthy aquatic communities.
Field and modeling studies were conducted in support of total maximum daily loads (TMDLs)for mercury in six south Georgia rivers and the Savannah River. Mercury is introduced to these rivers primarily by atmospheric deposition, with minor point source loadings. To produce mercury TMDLs in these rivers, the GIS-based Watershed Characterization System (WCS) and a mercury delivery spreadsheet were developed and applied with the water pollutant fate model WASP5. Together, these models calculate mercury buildup in watershed soils, loading and delivery through the watershed tributary system, and mercury fate in the mainstem rivers. Site specific mercury data are required for model parameterization. These models were applied to the seven rivers and their watersheds, and checked against survey data gathered during very dry conditions in June and July, 2000. Despite environmental variability and scientific uncertainties, calculated mercury concentrations in soils, sediment, and water compared reasonably well with the observed data in most watersheds. The accuracy of these model predictions within and among these watersheds is described. Sensitivity analyses point to those processes and parameters controlling mercury fate in these river systems, including atmospheric deposition, impervious watershed area, soil reduction rate constant, tributary reduction rate constant, and tributary methylation status. Future development should focus on mercury transport and transformation reactions in the tributary systems.