Synopsis: Although considerable measures are being enacted or proposed to reduce domestic emissions of mercury (Hg), there is the suggestion that increased Hg emissions from developing nations will result in an increase in atmospheric Hg to such a degree that domestic reductions will be overwhelmed. Although some data exist that suggest that some species of Hg will be deposited much closer to the emission source than others, there is little empirical evidence of this pattern. This connection is critical in order to effectively influence the regulation of remaining domestic controllable sources. We propose to couple the atmospheric Hg species to Hg deposition to watersheds along a depositional gradient by continously monitoring gaseous elemental mercury (GEM), particulate mercury (PM) and reactive gaseous mercury (RGM), and studying the spatial temporal pattern of Hg accumulation in the forest canopy and its subsequent washoff during rainfall events. Two forested study sites along an urban (Mississauga ON)-rural (Dorset ON) gradient will be studied using Tekran® monitoring instruments to explore the gradients in GEM, PM and RGM between sites closer to, and more distant from emission sources. We will establish two long-term high canopy chemistry monitoring towers where leaf surface chemistry and throughfall may be continously sampled. Finally, we will take our canopy accumulation results and couple them to measures of canopy characteristics derived from remote sensing data to derive more spatially extensive estimates of total deposition and loading potential to watersheds.

Chemicals Studied: The project will assess the relative the importance of Gaseous Elemental Mercury (GEM) Particulate mercury (PM) and Reactive Gaseous Mercury (RGM) to Hg accumulation in the forest canopy.

Geographic Areas: Two forested study sites along an urban (Mississauga,Ontario)-rural ( Dorset, Ontario) gradient

Project Duration: 2 years

Potential Results and Implications: By building on infrastructure that either already exists or is part of other parallel funded programs, the proposed work will have outcomes that are disproportionately great compared to the budget request. The data generated from this work will directly contribute to the understanding of the relationship between the very large pool of Hg present in the atmosphere, and the inputs of Hg to the watershed of which dry deposition is estimated to be at least 50% if
not more. The data will contribute directly to the development of empirical relationships between Hg emission and deposition at the local to regional scale. The importance of changes in accumulation on vegetated surfaces over the growing season, and the relative importance of canopy geometry and leaf area to estimating total throughfall and litterfall loads to watersheds will be demonstrated.The use of surrogate surfaces to estimate the accumulation of Hg on vegetated surfaces will be tested.

Project Contact:
Dr. Brian A. Branfireun
Associate Professor
Dept. of Geography at Mississauga
3359 Mississauga Road North, Mississauga Ontario, Canada L5L 1C6
Phone: (905) 569-4649
Email: brian.branfireun@utoronto.ca