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

汞的环境污染是全球关注的问题。由于叶面吸收大气中的汞，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生产剧毒甲基汞的热点，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。在整个东南部地区，有一个倡议，以恢复本地长叶松超过现有的火炬松。拟议的研究将研究森林恢复如何影响东南沿海平原森林的各种汞循环过程。这项工作将使人们更好地了解森林恢复如何影响汞在流域内的留存和有毒甲基汞的生产。拟议的工作将为来自北卡罗来纳州格林斯伯勒大学（UNCG）、少数民族服务机构、密歇根大学（U-M）和克莱姆森大学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的家庭教育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。主要研究人员将把这项研究纳入现有课程的教材，包括实地访问和案例研究，并向专业林业人员开展外联活动，向他们介绍林业做法如何改变汞循环。这项工作将通过研讨会、会议介绍和同行评审出版物广泛传播。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、间伐和皆伐）和长期森林恢复（恢复到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，在该流域，汞甲基化在排水不良的土壤中广泛存在。该项目将在桑蒂实验森林的一对流域进行，这是一个典型的沿海平原森林水源流域。具体而言，该项目将使用稳定的汞同位素比率来监测汞进入实验性森林流域的沉积路径，并区分河流输出的汞的沉积路径。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作期间和之后甲基汞形成和降解途径的深入了解。因此，拟议的工作将提供一个独特的机会来测试稳定的汞同位素的效用，以跟踪大气汞沉积和汞甲基化，并跟踪从不同来源吸收汞进入实验和参考流域的食物网。此外，将进行微观研究，以理清不同的环境因素及其对这些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地区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NSF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.