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MODELING PROCESSES CONTROLLING MERCURY FATE IN WATERSHEDS RECEIVING ATMOSPHERIC DEPOSITION - COMPARISON OF FIELD SCALE GLEAMS AND WATERSHED SCALE WCS-GBMM
Citation:
AMBROSE, R. B., I. X. TSIROS, T. A. WOOL, AND T. DAI. MODELING PROCESSES CONTROLLING MERCURY FATE IN WATERSHEDS RECEIVING ATMOSPHERIC DEPOSITION - COMPARISON OF FIELD SCALE GLEAMS AND WATERSHED SCALE WCS-GBMM. Presented at Eighth International Conference on Mercury as a Global Pollutant, Madison, WI, August 06 - 11, 2006.
Impact/Purpose:
The objective of this task is to develop, support and transfer a wide variety of tools and mathematical models that can be used to support watershed and water quality protection programs in support of OW, OSWER, and the Regions.
Description:
Long-term simulations of mercury fate in watersheds are needed to support regulations such as TMDLs and to predict the effectiveness of regulatory proposals, such as the Clean Air Mercury Rule (CAMR). Scientific uncertainties in mercury fate process descriptions combined with incomplete empirical datasets and gaps in available simulation technology have lead to significant levels of uncertainty in long-term predictions. These issues are investigated in a case study of mercury fate in Brier Creek, Georgia. Atmospheric deposition and soil concentration data were used along with simulation models to calculate mercury build-up and transport through Brier Creek watershed. Two linked models were used to examine watershed-scale terrestrial transport and fate of mercury: the Watershed Characterization System Mercury Tool (WCS) and the Grid-Based Mercury Model (GBMM). The more detailed GLEAMS-Hg was used to examine field-scale transport and fate of mercury, and to better constrain key parameters in the watershed-scale models. Brier Creek watershed was subdivided for the WCS-GBMM simulations. GLEAMS-Hg simulations were run on a set of fields within the watershed representing different land uses. Decadal-scale simulations were used to calibrate the models to recent soil mercury data. Finer scale simulations were run to calculate daily mercury loading under current conditions. Predicted runoff and erosion loadings were compared, and sensitivity analyses were conducted to determine the key parameters and forcing functions controlling long and short-term mercury loading from this watershed. This case study provides a realistic example of the capabilities and limitations of watershed mercury simulations. General spatial loading patterns and trends can be calculated, but specific spatial and temporal details in the simulations are uncertain. While uncertainties could be reduced with more data, better descriptions of mercury transport and fate processes are needed.