EAR-PF: Quantifying methane reactivity and turnover in the subterranean estuary: combined in-situ and ex-situ isotope tracer approaches

在海陆交界处，地下河口(STE)充当地下过渡带。STES可以支持影响营养物质和碳的浓度和运输的各种生物地球化学反应。甲烷(CH4)是一种重要的温室气体，也是全球碳循环中的主要参与者，在沿海次表层观察到了高浓度的甲烷。然而，这个CH4池在STES内转化和运输的方式仍然不受限制。这项研究将对甲烷如何在地下循环提供新的理解，特别是它的周转时间和控制浓度和命运的转化，就在释放到地表水之前。这些研究产品代表了基本的限制，这些限制对于确定次表层的CH4通量和STE在全球碳循环中的作用至关重要。斯蒂芬妮·威尔逊博士将在东海岸多个研究小组之前进行的工作的基础上，进一步科学地了解甲烷的循环以及地下与上覆水或大气之间的交换。这项研究的结果将直接适用于正在进行的研究和建模工作，提供有关甲烷的基本信息，为地下通量和排放量的计算提供信息，其影响超出地下水水文学和地球化学领域。此外，该项目旨在优化其调查结果的覆盖范围，并开发人力资本。结果将在会议、部门研讨会上传播，并在科学期刊上发表。威尔逊博士将让本科生参与实地和实验室的研究工作，目标是创造一个促进个人成长和科学学习的包容性环境。研究成果将通过几个途径向公众公布，这些途径旨在通过各种参与活动吸引K-12学生、教育工作者、当地社区和更大的公众。地下河口(STE)是地下的重要过渡带，承载着各种生物地球化学反应。它们是同时受分水岭和潮汐驱动因素影响的动力系统。在STE中，生物地球化学反应控制着地下营养物质和碳的形态和浓度，因此，它们决定了这些分析物被释放到上覆水和/或大气中时的命运。越来越多的文献报告说，沿海边缘的地下甲烷(CH4)浓度很高；然而，这个池的转化和运输机制仍然不清楚。因此，人们对这个地下甲烷池如何与上面的水和/或大气进行交换的了解是有限的。STE可以充当被动界面，含水层中产生的CH4可以保守地通过STE移动，或者CH4库存可以通过STE内的消费或生产进行修改，其时间尺度快于净运移。缺乏控制STE CH4池的背景和明确的限制，是确定次表层CH4通量和STE在全球碳循环中的作用所必需的知识差距。该项目包括采用一种三管齐下的办法，结合现场和非现场稳定同位素标记示踪实验以及地下地球化学梯度的特征，检查甲烷在固体废物中的转化和运输。这项工作涉及利率和机制。示踪剂实验将在美国东海岸的几个STE进行，这些STE被解析为两种主要的沿海STE类型，即湿地和沙地，并跨越了一系列水文强迫。这项研究的结果将对甲烷如何在地下循环提供新的理解，特别是它的周转时间和控制浓度和命运的转化，就在释放到地表水之前。具体地说，这项工作将提供有关CH4池周转、转化和运输的信息。这些产品代表了基本的限制，这对于确定次表层的CH4通量和STE在全球碳循环中的作用至关重要。这一新信息将直接适用于正在进行的确定过渡区在温室气体动力学和全球气候变化中的作用的研究。研究产品将提供基本信息，这些信息将超出地下水水文学和地球化学领域。结果将为STE思考的CH4大气通量模拟提供基本约束，该项目旨在优化其发现的影响范围并开发人力资本。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。

At the interface of land and sea, subterranean estuaries (STEs) serve as subsurface transition zones. STEs can support a variety of biogeochemical reactions that influence concentrations and transport of nutrients and carbon. High concentrations of methane (CH4), an important greenhouse gas and major player in the global carbon cycle, has been observed in the coastal subsurface. However, the way that this CH4 pool is transformed and transported within STEs remains unconstrained. This study will provide a novel understanding of how CH4 is cycled in the subsurface, specifically its turnover time and the transformations controlling concentration and fate, just prior to release to surface waters. These research products represent fundamental constraints, which are critical to determining fluxes of CH4 from the subsurface and the role of STEs in the global carbon cycle. Dr. Stephanie Wilson will build upon previous work conducted by multiple research groups along the east coast, to further scientific understanding of CH4 cycling and exchanges between the subsurface and the overlying water or atmosphere. The results of this study will be directly applicable to ongoing research and modeling efforts, providing fundamental information about CH4 to inform calculations of fluxes and emissions from the subsurface, with implications beyond the fields of groundwater hydrology and geochemistry. Moreover, the project is designed to optimize the reach of its findings and develop human capital. Results will be disseminated at conferences, departmental seminars, and published in scientific journals. Dr. Wilson will incorporate undergraduate students in both field and lab research efforts with the goal of creating an inclusive environment that promotes personal growth and scientific learning. Research findings will be made available to the public via several avenues designed to engage K-12 students, educators, the local community, and the larger public via a variety of engagement activities.Subterranean estuaries (STEs) are important transition zones within the subsurface that host a variety of biogeochemical reactions. They are dynamic systems influenced by both watershed and tidal drivers. Within the STE, biogeochemical reactions control the speciation and concentration of subsurface nutrients and carbon, therefore, they determine the fate of these analytes when they are released to the overlying water and/or the atmosphere. There is a growing body of literature reporting high concentrations of methane (CH4) in the subsurface along coastal margins; however, the mechanisms of transformation and transport of this pool remain unknown. There is, therefore, a limited understanding of how this subsurface CH4 pool exchanges with the overlying water and/or atmosphere. The STE may act as a passive interface whereby CH4 generated within the aquifer moves through the STE conservatively, or CH4 inventories may be modified via consumption or production within the STE on timescales faster than net transport. The lack of context and defined constraints controlling the STE CH4 pool represents a knowledge gap essential to determining fluxes of CH4 from the subsurface and the role STEs play in the global carbon cycle. The project includes examination of the transformations and transport of CH4 in STEs using a three-pronged approach that combines in situ and ex situ stable isotope labeled tracer experiments with the characterization of subsurface geochemical gradients. The work addresses rates and mechanisms. Tracer experiments will be conducted in several STEs along the east coast of the US parsed into the two dominant coastal STE types, wetland and sandy, and spanning a spectrum of hydrologic forcings. Results from this study will provide a novel understanding of how CH4 is cycled in the subsurface, specifically its turnover time and the transformations controlling concentration and fate, just prior to release to surface waters. Specifically, this work will provide information regarding the CH4 pool rate of turnover, transformation, and transport. These products represent fundamental constraints, which are critical to determining fluxes of CH4 from the subsurface and the role of STEs in the global carbon cycle. This novel information will be directly applicable to ongoing research determining the role of transition zones in greenhouse gas dynamics and global climate change. Research products will provide fundamental information, which will reach beyond the fields of groundwater hydrology and geochemistry. Results will provide fundamental constraints on modeling atmospheric fluxes of CH4 meditated by the STE and the project is designed to optimize the reach of its findings and develop human capital.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.