Collaborative Proposal: Response of mercury cycling to disturbance and restoration of low-gradient forested watersheds

汞的环境污染是一个全球关注的问题。由于叶面对大气汞的吸收，森林生态系统是汞污染的重要受体，而美国东南部的低梯度森林流域是高毒性甲基汞生产的热点，通过食用鱼类和其他高营养级食物来源对人类和野生动物构成风险。在整个东南地区，有一项倡议是在现有的火炬松上恢复本地长叶松。拟议的研究将检查森林恢复如何影响东南沿海平原森林的各种汞循环过程。这项工作将有助于进一步了解森林恢复如何影响流域内汞的滞留和有毒甲基汞的产生。拟议的工作将为来自北卡罗来纳大学格林斯博罗分校（UNCG）、少数族裔服务机构、密歇根大学（U-M）和克莱姆森大学（Clemson University）的不同学术背景的本科生和研究生提供独特的培训机会。此外，南卡罗来纳州沿海地区在家接受教育的学生将参与样本收集和处理，以便为这些缺乏资源的儿童群体提供更正式的STEM培训。主要调查人员将把这项研究纳入现有班级的教材，包括实地考察和个案研究，并向专业林务人员进行外联，使他们了解林业做法可能如何改变汞循环。这项工作将通过研讨会、会议报告和同行评议的出版物广泛传播。该项目建议使用稳定的汞同位素作为一种综合工具，以更好地了解短期森林干扰（规定的火灾、疏林和砍伐）和长期森林恢复（转向需水量较低的本地树种）对南卡罗来纳州低梯度沿海森林流域汞循环的影响，在那里，汞甲基化在排水不良的土壤中广泛存在。该项目将在Santee实验森林的成对流域进行，这是一个典型的沿海平原森林源头流域。具体而言，该项目将利用稳定的汞同位素比率监测汞进入试验性森林流域的沉积途径，并区分河流输出的汞的沉积途径。此外，在陆地和水生食物网组成部分中测量的甲基汞同位素将提供对实验流域森林操纵期间和之后甲基汞形成和降解途径的见解。因此，拟议的工作将提供一个独特的机会来测试稳定汞同位素在跟踪大气汞沉积和汞甲基化以及跟踪从不同来源进入实验和参考流域食物网的汞的吸收方面的效用。此外，还将进行微观研究，以弄清不同的环境因素及其对森林土壤中汞甲基化的影响。通过回答这些相互关联的问题，拟议的工作将能够揭示森林管理对北美东南部森林生态系统中汞沉积和甲基汞生产的影响。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Environmental pollution of mercury is a global concern. Due to foliar uptake of atmospheric mercury, forested ecosystem represents an important receptor of mercury pollution, while low-gradient forest watersheds in the southeastern United States represent hotspots for production of highly toxic methylmercury that poses a risk to humans and wildlife through consumption of fish and other high trophic level food sources. Throughout the southeastern region, there is an initiative to restore the native longleaf pine over the existing loblolly pine. The proposed research will examine how forest restoration affects various mercury cycling processes in southeastern coastal plain forests. This work will lead to an enhanced understanding of how forest restoration can affect the retention of mercury within watersheds and the production of toxic methylmercury. The proposed work will provide unique training opportunities for undergraduate and graduate students of diverse academic backgrounds from the University of North Carolina at Greensboro (UNCG), a minority serving institution, the University of Michigan (U-M), and the Clemson University. Also, home-schooled students in the coastal region of South Carolina will be involved in the sample collection and processing in order to provide a more formal STEM training to these groups of children lacking resources. The principal investigators will integrate this research into teaching materials of existing classes, including field visits and case studies, and also carry out outreach to professional foresters to inform them about how forestry practices may alter mercury cycling. The work will be widely disseminated through seminars, conference presentations, and peer-reviewed publications. The project proposes to use stable mercury isotopes as an integrative tool to better understand the effects of short-term forest disturbance (prescribed fires, thinning, and clear cut) and longer-term forest restoration (switching back to native tree species with lower water demand) on mercury cycling in a low-gradient coastal forested watershed in South Carolina, where mercury methylation is extensive in poorly drained soils. The project will take place in a paired watershed at Santee Experimental Forest, a typical coastal plain forest headwater watershed. Specifically, the project will use stable mercury isotope ratios to monitor depositional pathways of mercury into the experimental forested watershed and also to distinguish the depositional pathways of mercury exported by the streams. Further, methylmercury isotopes measured in terrestrial and aquatic food web components will provide insights into methylmercury formation and degradation pathways during and after forest manipulation in the experimental watershed. Thus, the proposed work will provide a unique chance to test the utility of stable mercury isotopes for tracking atmospheric mercury deposition and mercury methylation and for following uptake of mercury from different sources into the food webs of both experimental and reference watersheds. Further, microcosm studies will be conducted in order to disentangle different environmental factors and their effects on mercury methylation in these forest soils. Through answering these interrelated questions, the proposed work will be able to reveal the effects of forest management on mercury deposition and methylmercury production in a forested ecosystem in the southeastern region of North America.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.