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

汞是一种环境污染物，可对人类和野生动物造成神经毒性。由于大气环流模式和植物吸收，北半球排放的大量汞沉积在北极土壤中。然而，这种沉积的汞的命运仍然是一个活跃的争论领域，特别是在面对气候变化的情况下。虽然越来越多的证据表明，河流和海岸侵蚀是北冰洋汞的重要来源，但目前尚不清楚地下水如何影响汞通过土壤循环进入北冰洋河流和沿海地区。沿海含水层的化学环境将决定汞是被困在沿海沉积物中还是排入北冰洋，在北冰洋，汞可能会伤害鱼类、野生动物和依赖这些动物生存的社区。这项研究将量化汞的通量，并确定具有代表性的波弗特海泻湖系统中沿海含水层中汞的重要化学转化，该系统具有阿拉斯加波弗特海海岸线50%以上的特征。这些成果将与波弗特海沿岸的土著社区分享，项目研究人员将提供与感兴趣的社区成员进行公开对话的空间。这项研究工作还将支持美国鱼类和野生动物服务局正在进行的努力，以提高对影响北极国家野生动物保护区内鱼类和野生动物种群的陆地-海洋过程的了解，以及气候变化和发展可能如何影响沿海资源。这项研究将解决以下科学问题：(1)地下河口的溶解和土壤有机碳含量以及化学成分如何影响沉积物中汞的滞留或汞向沿海水域的排放？(2)冻结期和融化期地下水流量的季节差异如何影响汞进入波弗特海海岸的通量？(3)气候变化和永久冻土融化将如何影响可用于地下水动员的汞的量？这些问题将通过同位素(镭)、生物地球化学(有机碳)、水文(盐度、压力、温度、渗漏计)、选定的金属(铁和锰)以及陆地-泻湖地下水界面上的汞测量来解决。测量将从春季解冻，一直到夏末，直到冬季冻结。还将进行实验室实验，以辨别地下水和土壤化学对汞运输所涉及的化学物种的影响。未来的影响将通过测量永久冻土核心和未暴露的冻土中的汞，以及进行咸水入侵实验来探索。这项研究将为北极地区第一个汞盒子模型奠定基础，该模型包括测量的地下水贡献，在温带和热带地区被认为是沿海水域汞的重要贡献者。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.