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

汞是一种强效的神经毒素，其浓度经常超过人类和野生动物在原始淡水湖中食用的安全水平。汞的毒性最大的形式是甲基汞，这也是在野生动物和人类体内积累的汞的形式。控制环境中汞向甲基汞转化的环境因素是复杂的，美国东北部森林中汞的来源以及甲基汞生产和移动所涉及的环境条件尚不清楚。该项目旨在利用密歇根大学合作者开发的一种新兴分析技术，该技术依赖于对汞同位素质量的细微差异的辨别，以确定新英格兰北部湖泊中汞的来源，目标是推进这种尖端新方法的应用。重要的是，该方法的应用将显著提高目前对土壤和水中汞来源、甲基汞产生的潜力以及野生动物体内汞积累的认识。与密歇根大学合作的发展将为PI提供培训，并将大大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追踪输入并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。美国东北部森林流域的生物群受到高浓度甲基汞的影响，但流域甲基汞的产生和运输以复杂的方式受到景观特征（例如，湿地和开放水域连通性的百分比）和水化学（特别是溶解有机碳水平）的调节。在这项研究中，汞的稳定同位素将被分析，以破译甲基汞的来源到一个原始的，少营养湖泊的支流，并追踪汞在流域从这些支流转移到湖泊。生物体内的汞同位素特征可以识别生态系统长期积累的甲基汞。这些特征反映了在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生态系统中甲基汞的来源（例如，流域、湖内生产）和控制甲基汞形成的途径（例如，生物甲基化、光降解）。通过与密歇根大学的合作，并使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中的汞同位素特征，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)确定汞与有机碳络合作用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。本研究将建立汞同位素指纹图谱在无点源汞污染的流域中确定甲基汞的来源和产生途径，并为稳定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.