Doctoral Dissertation Research: The Impact of Thawing Permafrost on Coastal Groundwater and Mercury Cycling in the Arctic

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Mercury (Hg) is an environmental contaminant that can cause neurotoxicity in humans and wildlife. Due to atmospheric circulation patterns and plant uptake, a large amount of Hg emitted in the Northern Hemisphere is deposited in Arctic soils. However, the fate of this deposited Hg remains an active area of debate, particularly in the face of climate change. While growing evidence shows that rivers and coastal erosion are important sources of Hg to the Arctic Ocean, it is not presently understood how groundwater impacts Hg cycling through soils into Arctic rivers and coastal regions. The chemical environment of coastal aquifers will determine whether Hg is trapped in coastal sediments or discharged into the Arctic Ocean, where it has the potential to harm fish, wildlife, and the communities that depend on these animals to survive. This study will quantify Hg fluxes and identify important chemical transformations of Hg through the coastal aquifer in a representative Beaufort Sea lagoon system, which characterizes over 50% of the Alaskan Beaufort Sea coastline. These results will be shared with Indigenous communities along the Beaufort Sea coast, and project researchers will provide space for open dialogue with interested community members. The study work will also support ongoing efforts by the US Fish and Wildlife Service to improve understanding of land-ocean processes that impact fish and wildlife populations within the Arctic National Wildlife Refuge and how coastal resources may be impacted by climate change and development. The study will address the following scientific questions: (1) How do the dissolved and soil organic carbon content and the chemical composition of the subterranean estuary impact the retention in sediments or discharge of Hg into coastal waters? (2) How do seasonal differences in groundwater flow due to freeze-up and thaw periods impact the fluxes of Hg into the Beaufort Sea coast? (3) How will climate change and permafrost thaw impact the amount of Hg available for groundwater mobilization? These questions will be addressed with isotopic (radium), biogeochemical (organic carbon), hydrologic (salinity, pressure, temperature, seepage meters), select metals (iron and manganese), and Hg measurements across the land-lagoon groundwater interface. Measurements will be conducted from spring thaw, through late summer, and up to winter freeze-up. Laboratory experiments will also be conducted to discern the impact of groundwater and soil chemistry on the chemical species involved with Hg transport. Future impacts will be probed by measuring Hg in permafrost cores and unexposed tundra soils and performing saltwater intrusion experiments. This study will lay the groundwork for the first box model of Hg in the Arctic that includes measured groundwater contributions, known in temperate and tropical regions to be a significant contributor of Hg to coastal waters.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.