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Mercury cycling in terrestrial environments – an ecosystem perspective

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Monday, November 11, 2013

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Daniel Obrist
Research Professor
Division of Atmospheric Sciences
Desert Research Institute
Reno, NV

Terrestrial ecosystems serve as the key link between atmospheric deposition of Hg – the main pathway for Hg input in remote ecosystems – and mobilization to streams, lakes, and oceans where Hg pollution impacts wildlife and humans through consumption of Hg-laden fish. Terrestrial ecosystems act as reservoirs for atmospheric pollutant deposition via wet and dry deposition, but also increase deposition via leaf uptake and litterfall. While terrestrial Hg storage efficiently removes Hg from active cycling, the semi-volatile nature of elemental mercury also causes partial re-volatilization back to the atmosphere after deposition, a process estimated to account for up to 60% of current atmospheric Hg emissions. A particular concern is that such legacy emissions (i.e., re-emission of previously deposited pollutants) lead to continued cycling of past pollution and contribute to exposure that is delayed in time and displaced geographically from primary emission sources. Photochemical reduction processes at environmental surfaces are known to play a critical role in re-mobilizing Hg, but the underlying mechanisms and dynamics of terrestrial re-emissions are not well understood.

This presentation aims to provide insights into the dynamic cycling of mercury within ecosystems, with a particular emphasis on surface-atmosphere exchange processes. Using examples of ongoing and past research projects in our group, I will emphasize the importance of ecosystems in affecting regional and global mercury cycling with an emphasis on sorption and redox chemistry and importance of gas-phase re-emissions.

Host: Judith Perlinger

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