Identifying Cross-talk between Nitrogen and Manganese Redox Cycling

湿地等水生环境是许多化学元素发生变化的自然环境，这些变化在地球的生物地球化学循环中发挥着关键作用。这项研究的重点将是更详细地了解经历这种化学转化的两种重要元素：氮和锰之间的自然反应。水生环境中这些元素之间的反应对天然水中营养物质和金属污染物的动员、在地球大气-气候系统中发挥重要作用的气体的产生以及对地球早期历史上现代大气形成之前发生的反应的影响都有影响。这项研究将为研究生和博士后学者提供培训和指导机会，并将为伍兹霍尔海洋研究所本科生暑期研究员的教育做出贡献。研究人员将与波士顿绿色学院合作，向科学教师提供科学演示和教材，让来自代表性不足群体的各种学生有机会参与地球科学的研究经验。这项研究将为水生生态系统中相对鲜为人知的氮(N)和锰(Mn)之间的氧化还原反应耦合提供新的线索。虽然热力学条件通常有利于氮和锰之间的偶合反应，但发生这种反应的证据仍然是谜。这项研究将重新审视之前假设的锰和氮之间的反应，配备新的工具来研究锰和氮的形态和同位素行为，如先进的可溶和固相锰形态形成、多同位素分析和流动沉积物孵化。这些技术将被用来研究自然动态氧化还原区中的锰(III)-配体络合物和其他与环境相关的形式的N物种的非生物氧化动力学。研究小组将研究锰的活性形式，如锰(III)-配体络合物和无序的锰(III/IV)氧化物在N的非生物转化中的作用，以及这些非生物反应如何受到N和Mn的活性中间物种的生物产生的控制。其具体目标是量化还原N物种氧化过程中的反应动力学和相关的同位素效应，确定天然溶解有机碳对这些反应的影响，识别微生物形成的N和Mn中间体之间的反应，并研究自然条件下的耦合Mn和N反应。通过带来新的工具来理解自然动态氧化还原区域中的这些反应，这些结果将扩大我们对这些反应的快速理解，对水生生物地球化学、自然和人为氮的去向和运输、硝酸盐的双同位素特征的影响、污染物和营养物质的动员、含氮温室气体的产生以及大氧化事件之前早期地球反应的催化作用具有重要影响。该奖项反映了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。

Aquatic environments such as wetlands are natural settings in which many chemical elements undergo transformations that play critical roles in Earth's biogeochemical cycles. This research will focus on developing a more detailed understanding of natural reactions between two important elements that undergo such chemical transformations: nitrogen and manganese. Reactions between these elements in aquatic environments have implications for the mobilization of nutrients and metal contaminants in natural waters, the production of gases that play important roles in Earth's atmosphere-climate system, as well as implications for reactions that occurred during early Earth history before the formation of the modern atmosphere. The research will provide training and mentoring opportunities for a graduate student and postdoctoral scholar, and will contribute to the education of undergraduate summer student fellows at the Woods Hole Oceanographic Institution. The researchers will collaborate with the Boston Green Academy to provide science presentations and teaching materials to science teachers, giving a variety of students from underrepresented groups opportunities to participate in research experiences in the Earth sciences.This research will shed new light on the relatively poorly understood coupling of redox reactions between nitrogen (N) and manganese (Mn) in aquatic ecosystems. Although thermodynamic conditions are generally favorable for coupled reactions between N and Mn, evidence for the occurrence of such reactions has remained enigmatic. This research will revisit previously hypothesized reactions between Mn and N, armed with new tools for both Mn and N speciation and isotopic behavior such as advanced soluble and solid-phase Mn-speciation, multi-isotope analyses and flow-through sediment incubations. These techniques will be used to examine abiotic oxidation dynamics of N species by Mn(III)-ligand complexes and other environmentally relevant forms of Mn in naturally dynamic redox zones. The research team will examine the role of reactive forms of Mn such as Mn(III)-ligand complexes and disordered Mn(III/IV) oxides in abiotic transformation of N, and how these abiotic reactions are controlled by the biological production of reactive intermediate species of both N and Mn. The specific objectives are to quantify reaction kinetics and associated isotope effects during oxidation of reduced N species, determine the influence of natural dissolved organic carbon on these reactions, identify reactions between N and Mn intermediates formed by microbes, and examine coupled Mn and N reactions under natural conditions. By bringing new tools to understand these reactions in naturally dynamic redox zones, these results will expand our burgeoning understanding of these reactions, with important implications for aquatic biogeochemistry, fate and transport of natural and anthropogenic nitrogen, impacts of dual isotope signatures of nitrate, mobilization of contaminants and nutrients, production of N-bearing greenhouse gases, and catalysis of early Earth reactions before the Great Oxidation Event.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.