COMPOUND, ELEMENTAL, AND ISOTOPIC PERSPECTIVES ON MERCURY MOBILIZATION DURING THAW IN A DISCONTINUOUS PERMAFROST ZONE

• Main Author: Fahnestock, Maria F
• Format: Text
• Language: unknown
• Published: University of New Hampshire Scholars' Repository 2022
• Subjects: Arctic; climate change; mercury; permafrost; Abisko; Climate change; palsa
• Online Access: https://scholars.unh.edu/dissertation/2669; https://scholars.unh.edu/cgi/viewcontent.cgi?article=3668&context=dissertation

Arctic ecosystems are a major global sink for both carbon (C) and mercury (Hg), both of which are influenced by anthropogenic activities. The accelerated climate-change-induced warming documented in the Arctic has led to permafrost thaw resulting in landscape evolution from hydrological, vegetation and microbial shifts. All of these resulting changes have the potential to influence how Hg, a toxic contaminant, is mobilized and re-cycled in this ecosystem. In this body of work, I investigate patterns of Hg speciation, elemental abundances, and stable isotopes across the thaw gradient in a permafrost peatland and interconnected freshwater lakes in Abisko, Sweden to assess changes in Hg storage and in Hg export pathways. In Chapter 2 (republished from Fahnestock et al., 2019), I report results suggest that during initial stages of permafrost thaw, when the active layer in the palsa deepens, export of gas-phase mercury may be an important pathway of Hg loss. As the thaw continues vegetation changes to a Sphagnum-dominated semi-thawed ecosystem, where Hg export into the atmosphere limits accumulation of Hg in peat and the peat bound HgT pool is depleted. In the final stage of thaw, characterized by fully thawed fens, more labile organic matter and a diverse microbial community result in greater Hg retention in fen peat and higher levels of porewater MeHg that may be exported to nearby lakes and streams. Hg stable isotopes employed in Chapter 3 provide evidence supporting the importance of vegetation as an important sink of Hg in Arctic peatlands, show that photoreduction processes are important across the landscape and that ombrotrophic bogs may retain more Hg from wet deposition. Taken together, these findings suggest that Hg cycling in thawing peatlands will be influenced by future climatological patterns that drive the hydrological conditions, particularly the hydrologic connectivity, of this ecosystem. Chapters 4 and 5 consider the role of Arctic lakes in an ecosystem undergoing permafrost thaw. In Chapter 4, ...