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RARE Grant- Atmospheric Dry Deposition: Quantification of Mercury and Nutrients using Novel Surrogate Surface Collector Techniques
Impact/Purpose:
Excessive levels of mercury and nutrients in our nation's waters are the most widespread cause of water quality impairment in the US. Atmospheric emissions and deposition processes are important drivers in mercury accumulation in soils and sediments, and are now recognized as the major route of contamination to most aquatic ecosystems. It was previously assumed that RGM dry deposition was equally as important as wet deposition. The results of a recent study in Dearborn, MI indicate that dry deposition in source-impacted areas can be a factor of three higher than wet deposition. Atmospheric constituents are scavenged by rainfall for only a small fraction of the year while dry deposition, less understood and less tractable to model, is omnipresent. Thus field studies of mercury and nutrients dry deposition of any sort are few because of the minuscule but near-continuous nature of dry deposition processes and the lack of reliable methods to directly measure dry deposition of gaseous mercury and nitrogen species. The study will demonstrate the utility of a surrogate turf sampler as well as a new automated surface water dry deposition collector and the associated analytical methods to quantify and identify the sources of atmospheric dry deposition. The study will generate the first long term daily mercury dry deposition data set that will be useful to evaluate and improve contemporary model algorithms. The model improvements may have wide application in deterministic/predictive models used for (i) calculating spatially gridded deposition fields for aquatic bioaccumulation models, and (ii) evaluating emission reduction scenarios and regulatory support. The monitoring and modeling tools to be developed/evaluated during this proposed study will have broad applicability to States in the development of TMDLs and in the evaluation of large point source to near-field atmospheric deposition impacts (Hotspots).
Description:
This study will quantify the daily surrogate surface dry deposition of mercury and nutrient species, and evaluate its relative importance to wet deposition at two sites in Florida over a two-year period. It will identify the major sources contributing to the observed mercury and nutrient dry deposition through a comprehensive multi-variate receptor and hybrid modeling effort and evaluate the importance of local, urban, and regional contributions. The importance of vegetative surrogate surface structure characteristics to the magnitude of dry deposition collected will be evaluated as well as dry deposition to surface water. Ultimately, the study will investigate the linkages between ambient mercury and nutrient concentrations and surrogate surface dry deposition to evaluate the efficacy of contemporary dry deposition models.