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

盐沼代表着陆地和海洋之间的交界，是一个极其重要的生态系统，它保护大陆免受风暴的侵袭，同时提供多种有价值的服务，包括鱼类和贝类的育苗场，过滤陆源废物，以及向沿海海洋出口营养物质和食物来源。然而，由于海平面加速上升和沉积物供应减少，台地沼泽现在濒临灭绝，这两个因素共同可能导致它们溺水。该项目将研究主要风暴如何通过转移沿海地区的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。这种沉淀层(一英寸或更多)有助于沼泽垂直生长，为沼泽提供养分，并提高盐沼草的生产力。这项研究将使人们了解风暴是如何产生这些沉积物的，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，调查人员将设计和促进一门关于风暴与海岸线相互作用的研究生级课程，涵盖与风暴影响有关的水动力学、沉积物动力学、地貌学、生态学、人文地理学和经济学的各个方面。其他更广泛的影响包括：1)促进与当地利益攸关方(包括佐治亚州海岸生态系统长期生态研究网站)建立新的和现有的关系，以促进数据交换、培养合作和传播研究结果；2)维护一个项目网站，展示项目的动机、进展、研究生课程的细节，并提供数据产品的链接；3)培训一名博士后研究员、一名博士后以及至少两名本科生和两名高中实习生；4)通过开展将在弗吉尼亚海洋科学研究所实施的动手K-12学习活动，直接向公众宣传。这项研究利用2017年12月在佐治亚州萨佩洛岛后面收集的一套沉积物岩芯和沼泽表面样本，以量化与飓风伊尔玛有关的沉积物沉积的来源(得到美国国家科学基金会地貌和土地利用动力学计划的快速赠款的支持)。IRMA后数据将补充来自近岸、后屏障(河道、湾底、潮滩、沼泽边缘侵蚀)和河流环境中潜在沉淀物来源的额外样本。这些来源对风暴沉积物的相对贡献将使用通过主成分分析和非计量多维尺度统计分析的沉积学(例如，粒度、着火损失、有孔虫含量)和地球化学(生物标记物成分、散体沉积物和生物标记物稳定和放射性同位素成分)的新组合来确定。风暴潮高程、当地水流模式、沉积物厚度和沉积物来源之间的关系将使用多维统计工具进行分析。然后，这些数据将与Delft3D模型结合使用，Delft3D模型可以模拟IRMA和其他风暴条件下的水动力学、泥沙输送和由此产生的沉积模式，以：1)探索一系列后屏障亚环境中的风暴沉积来源，2)确定近岸、后屏障和河流水库在主要风暴期间为盐沼提供沉积物的相对重要性，3)量化向沼泽平台分布沉积物的过程、路径和机制(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)，以及4)评估风暴沉积相对于长期垂直沼泽淤积的重要性。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。

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.