| Summary: | Mercury (Hg) is a toxic and globally distributed contaminant that poses a serious risk to humans, wildlife, and the environment due to its ability to bioaccumulate along the food webs in aquatic ecosystems. The overarching goals for this dissertation are to: (1) evaluate the potential of mass-independent fractionation (MIF) of Hg during photochemical reactions to understand biogeochemical Hg cycling in natural systems; and (2) utilize Hg mass-dependent (MDF) and mass-independent fractionation (MIF) to characterize and trace Hg sources in the environment. In Chapter 2, Hg isotopes link environmental factors to Hg MIF preserved in freshwater lower trophic organisms to quantify MMHg photodegradation in freshwaters and understand how Hg MIF is preserved in natural systems. In Chapter 3, Hg isotopes in pelagic ocean higher trophic biota assess the relative contribution of Hg sources, transformation processes (methylation/photodemethylation), and other factors that may control the Hg isotopic signature of open-ocean fish in different regions and depths of the pelagic ocean. Chapter 4 assess Hg isotopes in atmospheric gaseous Hg(0), particulate Hg (PHg), and snow to understand Hg photochemical processes and sources in the Arctic. This dissertation demonstrates source characterization of atmospheric Hg species from multiple emission sources and better understanding of transformation processes that alter Hg source signatures, and highlights the potential of stable Hg isotopes to contribute to the increasing knowledge of Hg sources and transformation processes in the atmosphere, aqueous ecosystems and cryosphere. Ph.D.
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