RII Track-4: Deciphering sources and accumulation pathways of mercury in the tributaries and lake of a forested watershed using stable mercury isotopes

非技术描述汞是一种强有力的神经毒素，在来自原始淡水湖的鱼类中，汞的浓度经常超过人类和野生动物食用的安全水平。汞的毒性最大的形式是甲基汞，这也是积累在野生动物和人类体内的汞的形式。控制汞在环境中转化为甲基汞的环境因素很复杂，汞的来源以及整个美国东北部森林中甲基汞的生产和转移所涉及的环境条件还没有得到很好的了解。该项目旨在使用密歇根大学合作者开发的一种新的分析技术，该技术依赖于汞同位素质量之间的细微差异的区分，以确定新英格兰北部一个湖泊中汞的来源，目的是促进这一尖端新方法的应用。重要的是，这种方法的应用将大大提高目前对土壤和水中汞的来源、甲基汞的生产潜力以及野生动物汞积累的了解。与密歇根大学合作的发展将为PI提供培训，并将显著扩大她在达特茅斯大学的研究能力。技术描述汞同位素比率的自然变异性已被用于跟踪输入和确定调节甲基汞水平的过程，甲基汞是生物群吸收的有毒形式的汞。美国东北部森林集水区的生物群受到高浓度甲基汞的影响，但流域中甲基汞的产生和运输受到景观特征(例如湿地和开阔水域连通性的百分比)和水化学(特别是溶解有机碳水平)的复杂方式的调节。在这项研究中，将对汞的稳定同位素进行分析，以破译一个原始的、富营养化湖泊支流的甲基汞的来源，并追踪分水岭中汞从这些支流向湖泊的转移。生物体中的同位素汞特征可以确定生态系统长期积累的甲基汞的指纹。这些特征反映了生物吸收之前发生的转化(即汞甲基化和去甲基化)，使它们能够用于区分甲基汞的来源(例如，流域、湖泊生产)和控制生态系统中甲基汞形成的途径(例如，生物甲基化、光降解)。通过与密歇根大学的合作，并利用合作者的分析仪器和设施，将确定来自支流和湖泊的生物群的汞同位素特征，以：1)解释具有不同景观特征的溪流中控制甲基汞水平的来源和途径；2)确定汞与有机碳的络合对汞同位素特征的影响；3)确定原始湖泊中甲基汞的主要来源。这项工作将建立使用汞同位素指纹来确定没有汞污染点源的分水岭中甲基汞的来源和生产途径，并为稳定的汞同位素特征提供有价值的新应用。

Non-technical DescriptionConcentrations of mercury, a potent neurotoxin, frequently exceed levels safe for consumption by humans and wildlife in fish from pristine, freshwater lakes. The most toxic form of mercury is methylmercury, which is also the form of mercury that accumulates in wildlife and humans. The environmental factors that control the transformation of mercury to methylmercury in the environment are complex, and the sources of mercury and the environmental conditions involved in production and movement of methylmercury throughout the forests of the northeastern United States are not well understood. This project aims to use an emerging analytical technique developed by collaborators at the University of Michigan that relies on discrimination between subtle differences in the masses of mercury isotopes to identify the sources of mercury in a northern New England lake, with the goals of advancing the application of this cutting-edge new method. Importantly, application of this method will significantly improve current understanding of the sources of mercury in soil and water, the potential for production of methylmercury, and the accumulation of mercury in wildlife. Development of the collaboration with the University of Michigan will provide training for the PI and will significantly expand her research capacity at Dartmouth University.Technical DescriptionNatural variability in mercury isotope ratios have been used to trace inputs and identify processes that regulate levels of methylmercury, the toxic form of mercury that is taken up by the biota. Biota in forested catchments of the northeastern United States are subject to high concentrations of methylmercury, but the production and transport of methylmercury in watersheds are mediated in complex ways by landscape characteristics (e.g., percent wetland and open water connectivity) and water chemistry (especially dissolved organic carbon levels). In this study, stable isotopes of mercury will be analyzed to decipher the sources of methylmercury to the tributaries of a pristine, oligotrophic lake, and to trace the transfer of mercury in the watershed from these tributaries to the lake. Isotopic mercury signatures in organisms can fingerprint methylmercury accumulated from the ecosystem over long time periods. These signatures reflect transformations (i.e., mercury methylation and demethylation) that occurred prior to biological uptake, allowing them to be used to distinguish sources of methylmercury (e.g., watershed, in-lake production) and pathways controlling methylmercury formation (e.g., biotic methylation, photodegradation) in the ecosystem. Through collaboration with the University of Michigan, and access to the collaborator's analytical instrumentation and facilities, mercury isotopic signatures will be determined in biota from the tributaries and the lake to: 1) explain sources and pathways controlling methylmercury levels across streams with varying landscape characteristics; 2) determine the effect of mercury complexation to organic carbon on mercury isotope signatures; and 3) identify major sources of methylmercury to fish in a pristine lake. This work will establish the use of mercury isotopic fingerprints to determine sources and production pathways of methylmercury in a watershed with no point-sources of mercury contamination, and provide a valuable new application of stable mercury isotope signatures.