Collaborative Research: Hurricane Sedimentation on Salt Marshes: Extent, Provenance, and Processes

盐沼代表了陆地和海洋之间的界面，是一个至关重要的生态系统，它保护大陆免受风暴侵袭，同时提供多种有价值的服务，包括鱼类和贝类的温床，过滤陆地产生的废物，以及向沿海海洋出口营养物质和食物来源。然而，由于海平面的加速上升和沉积物供应的减少，平台沼泽现在正处于濒危状态，这两者加在一起可能导致它们被淹没。该项目将研究大风暴如何通过从沿海地区转移沉积物并将其沉积在沼泽顶部的广泛层中来帮助沼泽的可持续性。这个沉淀层（一英寸或更多）有助于沼泽垂直堆积，为沼泽提供营养，并提高盐沼草的生产力。这项研究将有助于了解风暴如何产生这些沉积物，以及近岸和沼泽系统的特征如何影响洪水的方向以及由此产生的悬浮沉积物的分布和沉积。作为一项更广泛的影响活动，研究人员将设计并促进一门关于风暴与海岸线相互作用的研究生课程，涵盖与风暴影响相关的水动力学、泥沙动力学、地貌学、生态学、人文地理学和经济学等方面。其他更广泛的影响包括：1)促进与当地利益相关者（包括佐治亚海岸生态系统长期生态研究网站）的新的和现有的关系，以促进数据交换，培养合作，并传播研究结果；2)维护一个项目网站，展示动机，进展，研究生课程的细节，并提供数据产品的链接；3)培养博士后1人，博士生1人，本科生2人以上，高中实习生2人以上；4)通过在弗吉尼亚海洋科学研究所实施的K-12实践学习活动的发展，直接与公众接触。该研究利用了2017年12月在佐治亚州萨佩洛岛后面收集的一套沉积物岩心和沼泽表面样本，以量化与飓风伊尔玛相关的沉积物沉积物的来源（由美国国家科学基金会地貌和土地利用动态计划的RAPID资助）。厄玛飓风后的数据将补充来自近岸、后屏障（海峡、海湾底、潮滩、沼泽边缘侵蚀）和河流环境内潜在沉积物来源的额外样本。通过主成分分析和非度量的多维尺度统计，利用沉积学（如粒度、着火损失、有孔虫含量）和地球化学（生物标志物组成、体沉积物和生物标志物稳定同位素和放射性同位素组成）指标的新组合来确定这些来源对风暴沉积物的相对沉积贡献。将使用多维统计工具分析风暴潮高程、局部水流模式、沉积物厚度和沉积物物源之间的关系。然后，这些数据将与Delft3D模型结合使用，该模型可以模拟厄玛和其他风暴条件下的水动力学、沉积物运输和由此产生的沉积模式，从而：1)在一系列后屏障亚环境中探索风暴沉积物的来源；2)确定近岸、后屏障和河流水库在大风暴期间向盐沼提供沉积物的相对重要性；3)量化沉积物向沼泽平台分布的过程、途径和机制（例如，风暴潮水平和持续时间、波浪暴露、当地地貌和河流沉积物排放）；4)评价风暴沉积相对于长期垂直沼泽增生的重要性。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。

Salt marshes represent the interface between land and sea and are a vitally important ecosystem that protects the mainland from storms while providing a multitude of valuable services including nursery grounds for fish and shellfish, filtering land-derived wastes, and exporting nutrients and food sources to the coastal ocean. However, platform marshes are now endangered due to accelerating sea-level rise and diminished sediment supplies, which together may lead to their drowning. This project will study how major storms help the sustainability of marshes by transferring sediment from the coastal zone and depositing it in a widespread layer on top of the marsh. This sediment layer (an inch or more) helps the marsh to accrete vertically, fertilizes the marsh with nutrients, and enhances the productivity of the salt marsh grasses. This research will produce an understanding of how storms source these sediments and how characteristics of the nearshore and marsh system influence the direction of floodwaters and the resulting distribution and deposition of the suspended sediment. As a broader impacts activity, the investigators will design and facilitate a graduate-level course on the Interaction of Storms with the Coastline, covering aspects of hydrodynamics, sediment dynamics, geomorphology, ecology, human geography, and economics as they relate to storm impacts. Additional broader impacts include: 1) fostering new and existing relationships with local stakeholders (including the Georgia Coastal Ecosystems Long Term Ecological Research site) to facilitate data exchange, cultivate collaboration, and disseminate findings, 2) maintaining a project website presenting details of the motivation, progress, the graduate course, and providing links to data products; 3) training one postdoctoral researcher, one Ph.D. student, and at least two undergraduate students and two high school interns; and 4) direct outreach to the public through development of hands-on K-12 learning activities to be implemented at the Virginia Institute of Marine Science.The study leverages a suite of sediment cores and marsh surface samples collected behind Sapelo Island, Georgia, in December 2017 to quantify the provenance of sediment deposits associated with Hurricane Irma (supported by a RAPID grant from the NSF Geomorphology and Land-use Dynamics Program). Post-Irma data will be supplemented with additional samples from potential sediment sources within nearshore, backbarrier (channel; bay floor; tidal flat; marsh-edge erosion), and fluvial environments. The relative sediment contributions from each of these sources to the storm deposit will be determined using a novel combination of sedimentologic (e.g., grain size, loss-on- ignition, foraminifera content) and geochemical (biomarker compositions, bulk-sediment and biomarker stable- and radio- isotopic compositions) proxies analyzed through principal component analysis and non- metric multi-dimensional scaling statistics. Relationships among storm-surge elevation, local flow patterns, deposit thickness, and sediment provenance will be analyzed using multi-dimensional statistical tools. These data will then be used in conjunction with a Delft3D model, which can simulate hydrodynamics, sediment transport, and resulting sedimentation patterns during Irma and other storm conditions, to: 1) explore the source of storm deposits across a range of backbarrier subenvironments, 2) determine the relative importance of nearshore, backbarrier, and fluvial reservoirs in providing sediment to saltmarshes during major storms, 3) quantify the processes, pathways, and mechanisms of sediment distribution to the marsh platform (e.g., storm-surge level and duration, wave exposure, local geomorphology, and river sediment discharge), and 4) evaluate the importance of storm sedimentation relative to long-term vertical marsh accretion.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.