RAPID: Collaborative Research: Marsh Sedimentation due to Hurricanes Florence and Michael Flooding Event in SC

RAPID：合作研究：佛罗伦萨飓风和南卡罗来纳州迈克尔洪水事件造成的沼泽沉积

• 批准号: 1904496
• 负责人: Christopher Hein
• 金额: $ 1.22万
• 依托单位: College of William & Mary Virginia Institute of Marine Science
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-12-01 至 2019-11-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1904496&HistoricalAwards=false
• 关键词: RAPID; Collaborative; Research; Marsh; Sedimentation

Hurricanes are responsible for the destruction of sandy shorelines and devastation to coastal cities and residential communities. However, scientists have recently begun to recognize that they can have net positive influences on some coastal systems. In particular, although storm waves may cause surface excavation and erosion of the marsh edge in coastal wetlands, hurricanes may also cause net sedimentation during storm surge inundation: storm waves and currents stir sediment off the bottom in the nearshore and within bays and deposit this suspended sediment on marshes during the accompanying storm surge. Although this process is infrequent, a single hurricane can add more inorganic sediment to the marsh surface than is emplaced by daily processes acting over several decades. It has also been shown that marsh plant communities benefit from storm sedimentation due to the added nutrients derived from the new mud. Thus, hurricanes can significantly increase the resiliency of marshes and help their sustainability in a regime of accelerating sea-level rise. This past September, Hurricane Florence was predicted to be a category 4 hurricane and wreak havoc along the North Carolina coast. However, upper wind shear significantly reduced wind velocities, downgrading the storm to a category 1 hurricane by the time it made landfall. Still as the hurricane moved inland, precipitation associated with the storm deluged coastal regions of North and South Carolina with 6 to 20 inches of rain. This amount of rain over a three day period greatly increased the stage and discharge of local rivers, several of which empty directly into Winyah Bay in central South Carolina. These flood waters carried large plumes of suspended sediment to the coastal ocean and to the proximal marshes. We plan to measure this river-derived sediment in the Cape Romain region and compare this sedimentation event to storm-surge-derived deposits mapped in 2017 following Hurricane Irma.The major goal of this study is to document the potential benefits of increased rates of inorganic sedimentation caused by Hurricanes Florence and Michael to the marsh system backing the Cape Romain cuspate foreland. Unlike Hurricane Irma in 2017, which generated high-energy waves, strong onshore winds, and a 1 m storm surge, and resulted in the deposition of a 1-2 cm thick mud layer, Hurricanes Florence and Michael had little direct impact on the marshes of central South Carolina due to their weaker winds and less impactful storm tracks. However, Florence, and to a much lesser extent Michael, produced intense precipitation, which vastly increased the stage and discharge of coastal rivers by an order of magnitude. Several of these rivers carried floodwaters and substantial quantities of suspended sediment directly into Winyah Bay and nearby marsh systems. Repeat coring of the Cape Romain marshes at locations previously sampled following Hurricane Irma would provide a rare opportunity to compare a high riverine sedimentation event to that produced by an energetic hurricane. We will revisit and resample our Cape Romain locations (10 stations along two transects), as well as measure our ten long-term SET sites near Muddy Bay (in Cape Romain). In addition, at least four other sites along the transects will be occupied to ensure broad spatial coverage of the hurricane-related deposit. Sediment cores, shallow surface sediment samples, and observations would be taken at each station to document new sedimentation, and determine if we can differentiate sediment delivered by each Hurricane Irma (wave- and storm-surge- induced from ambient sediment) and Hurricane Florence (introduction of new riverine sediment). The latter will be done via observations, sedimentological analyses (grain size, texture, physical structures, color) of short sediment cores and bulk geochemical analyses (TOC, TN, delta13CTOC, delta15NTN) of surface samples associated with each Hurricanes Irma and Hurricanes Florence/Michael. In addition, our existing SET records would be examined to determine if they capture past storm-associated spikes in sedimentation. Funds from NSF support field sampling and the lab processing and geochemical analyses of 20 surface sediment samples (10 each from Irma and Florence/Michael), and short-core analysis from our 10 cores to be collected at new sampling stations.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.

飓风造成沙滩海岸线的破坏以及沿海城市和住宅社区的破坏。然而，科学家最近开始认识到它们可以对一些沿海系统产生净积极影响。特别是，尽管风暴波浪可能会导致沿海湿地沼泽边缘的表面开挖和侵蚀，但飓风也可能在风暴潮淹没期间造成净沉积：风暴波浪和洋流将沉积物从近岸和海湾内的底部搅动，并使悬浮的沉积物沉积下来。伴随风暴潮期间沼泽上的沉积物。尽管这一过程并不常见，但一次飓风可以向沼泽表面添加的无机沉积物比几十年来日常过程所产生的沉积物还要多。研究还表明，由于新泥中添加了营养物质，沼泽植物群落受益于风暴沉积。因此，飓风可以显着提高沼泽的恢复能力，并有助于其在海平面加速上升的情况下的可持续性。去年 9 月，飓风“佛罗伦萨”预计为 4 级飓风，对北卡罗来纳州海岸造成严重破坏。然而，高空风切变显着降低了风速，导致风暴在登陆时降级为 1 级飓风。随着飓风向内陆移动，与风暴相关的降雨给北卡罗来纳州和南卡罗来纳州的沿海地区带来了 6 至 20 英寸的降雨量。三天的降雨量大大增加了当地河流的水位和流量，其中几条河流直接流入南卡罗来纳州中部的温亚湾。这些洪水将大量的悬浮沉积物带到沿海海洋和附近的沼泽地。我们计划测量罗曼角地区的这种河流沉积物，并将该沉积事件与 2017 年飓风艾尔玛之后绘制的风暴潮沉积物进行比较。这项研究的主要目标是记录无机盐比率增加的潜在好处佛罗伦萨飓风和迈克尔飓风对罗曼角尖端前陆的沼泽系统造成的沉积物。与2017年的飓风“艾尔玛”产生高能波浪、强烈的陆上风和1 m的风暴潮，并导致沉积1-2厘米厚的泥层不同，飓风“佛罗伦萨”和“迈克尔”对沼泽地的直接影响很小南卡罗来纳州中部的风力较弱，风暴路径影响较小。然而，佛罗伦萨和迈克尔（程度要小得多）产生了强烈的降水，使沿海河流的水位和流量大大增加了一个数量级。其中几条河流将洪水和大量悬浮沉积物直接带入温亚湾和附近的沼泽系统。在飓风“艾尔玛”之后采样的地点重复对罗曼角沼泽进行取芯，将提供一个难得的机会，将高河流沉积事件与强力飓风产生的沉积事件进行比较。我们将重新访问并重新采样我们的罗曼角位置（沿着两条横断面的 10 个站点），并测量 Muddy Bay（位于罗曼角）附近的 10 个长期 SET 站点。此外，沿横断面至少有四个其他地点将被占用，以确保飓风相关沉积物的广泛空间覆盖。将在每个站点采集沉积物核心、浅表沉积物样本和观测结果，以记录新的沉积物，并确定我们是否可以区分每次飓风艾尔玛（由周围沉积物引起的波浪和风暴潮）和飓风佛罗伦萨（由周围沉积物引起的波浪和风暴潮）带来的沉积物。引入新的河流沉积物）。后者将通过观察、短沉积岩芯的沉积学分析（粒度、质地、物理结构、颜色）以及与飓风艾尔玛和飓风佛罗伦萨/相关的表面样本的大量地球化学分析（TOC、TN、delta13CTOC、delta15NTN）来完成。迈克尔.此外，我们现有的 SET 记录将被检查，以确定它们是否捕获了过去与风暴相关的沉积峰值。 NSF 提供的资金支持对 20 个表面沉积物样本（Irma 和 Florence/Michael 各 10 个）进行现场采样、实验室处理和地球化学分析，以及对在新采样站收集的 10 个岩心进行短岩心分析。该奖项反映了 NSF法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。