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PREDICTING ENVIRONMENTAL CONCENTRATIONS OF AIRBORNE POLLUTANTS IN TERRESTRIAL RECEPTORS: THE CASE OF MERCURY
Citation:
Ambrose Jr., R B., I. X. Tsiros, AND T. A. Wool. PREDICTING ENVIRONMENTAL CONCENTRATIONS OF AIRBORNE POLLUTANTS IN TERRESTRIAL RECEPTORS: THE CASE OF MERCURY. Presented at 8th International Conference on Environmental Science and Technology, Lemnos, Greece, September 8-10, 2003.
Impact/Purpose:
Improve the scientific understanding of the processes controlling nutrient distributions in surface waters. Produce a suite of enhanced models for characterizing nutrient distributions in surface waters by incorporating improved process understanding in existing models (e.g., WASP), by developing new models (e.g., WHAM, reactive transport), and improving linkages between model components.
Description:
The question of mercury in the environment has rapidly become one of the high-profile environmental issues in several countries and internationally. There are environmental and human health concerns associated with elevated levels of mercury linked to industrial mercury emissions. Natural and anthropogenic emissions to the atmosphere can subsequently be released by deposition to terrestrial receptor sites such as watershed soils and surface waters. Recent studies have demonstrated that airborne mercury is the dominant source of mercury to watersheds in many areas, and that similar atmospheric mercury inputs will result in different mecury levels in fish as the result of differences in chemistry and dynamics of the water body, the hydrologic response of the watershed, and the form of mercury deposited to the watershed. Therefore, agencies involved in the regulation of mercury and the development of mercury policy need data and tools that will assist them in assessing and managing mercury risks and to support programs aimed at reducing mercury loading. For example, the US EPA's total maximum daily load (TMDL) program is used to set the maximum load of pollutants that can be discharged within a given impaired water of a catchment that receives pollutant contributions from both air and water or just air. Determination of TMDLs for mercury in watersheds must therefore include point source discharges to the water as well as atmospheric deposition resulting from nearby and distant atmospheric emissions and natural background sources. Atmoshperic deposition can occur directly onto the aquatic systems as well as to the watershed, where it may accumulate in the soils, with a fraction ultimately delivered to the surface water network. The TMDL must quantify the contributions of Hg to the terrestrial and aquatic systems in a catchment from local, regional and global sources. To address this need, a platform for atmospheric mercury deposition monitoring and source attribution is required along with a combination of transport/fate model development and process studies.
This paper presents a modeling analysis of airborne mercury fate in catchments which are important receptors in terms of exposure to mercury. The analysis is performed by coupling components of simulation models developed and published previously by the authors. Results from comparison of observational and simulated data for individual river catchments in the context of TMDLs in Georgia, USA are presented. The results obtained offer some degree of confidence in the model's ability to relate readily available environmental parameters to mercury fluxes in catchments. In addition, since loading of mercury deposited from the atmosphere onto the catchment soils is of major importance, a sensitivity analysis is performed to evaluate parameters controlling the predicted mercury loading flux, including intra- and inter-annual weather variability, landscape characteristics and other environmental parameters. Scenarios representing soils with different landscape and hydrologic transport characteristics were developed and simulations were designed to calculate mercury flux response to microclimatic and other environmental variables for several mercury concentration level scenarios.
The predictions presented in this work can be useful tools since they might allow air pollution control officials to better evaluate the fate of airborne mercury deposited onto terrestrial receptor sites when considering technological approaches to managing and reducing mercury releases in the environment. We conclude, finally, that the models used in the present study are suited for use in linked atmospheric-hydrologic mercury modeling studies for assessing acceptable loadings of mercury to the atmosphere to protect environmental quality in watersheds. Such linked modeling systems will be critical for assessing multiple interactive stressors and for evaluating the effectiveness of criterion-based restoration goals.