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.

飓风造成桑迪海岸线的破坏以及沿海城市和居民区的破坏。然而，科学家们最近开始认识到，它们可以对一些沿海系统产生净积极影响。特别是，虽然风暴波可能会造成沿海湿地的表面挖掘和沼泽边缘的侵蚀，但飓风也可能在风暴潮淹没期间造成净沉积：风暴波和水流搅动近岸和海湾内的沉积物，并在伴随的风暴潮期间将这些悬浮沉积物存款在沼泽上。虽然这一过程并不频繁，但一次飓风给沼泽表面带来的无机沉积物比几十年来每天发生的过程所造成的沉积物还要多。研究还表明，沼泽植物群落受益于风暴沉积，因为新泥浆增加了营养。因此，飓风可以大大增加沼泽的复原力，并有助于它们在海平面加速上升的情况下的可持续性。今年9月，飓风佛罗伦萨被预测为4级飓风，并沿着北卡罗来纳州海岸沿着。然而，上层风切变显著降低了风速，风暴登陆时已降级为一级飓风。随着飓风向内陆移动，北卡罗来纳州和南卡罗来纳州沿海地区因风暴带来的降水量达到6至20英寸。这三天的降雨量大大增加了当地河流的水位和流量，其中几条直接流入南卡罗来纳州中部的温雅湾。这些洪水沃茨将大量的悬浮沉积物带到沿海海洋和附近的沼泽。我们计划在Cape Romain地区测量这一河流沉积物，并将这一沉积事件与2017年飓风Irma之后绘制的风暴潮沉积物进行比较。本研究的主要目标是记录飓风佛罗伦萨和迈克尔导致的无机沉积速率增加对支持Cape Romain尖状前陆的沼泽系统的潜在好处。与2017年的飓风伊尔玛不同，飓风伊尔玛产生了高能量波浪，强烈的陆上风和1米的风暴潮，并导致1-2厘米厚的泥层沉积，飓风佛罗伦萨和迈克尔对南卡罗来纳州中部的沼泽几乎没有直接影响，因为它们的风力较弱，风暴路径影响较小。然而，佛罗伦萨和迈克尔都产生了强烈的降水，这大大增加了沿海河流的水位和流量。其中几条河流携带洪水和大量悬浮泥沙直接进入Winyah湾和附近的沼泽系统。在飓风“厄玛”之后先前取样的地点对罗曼角沼泽地重复取芯，将提供一个难得的机会，将高河流沉积事件与强飓风产生的沉积事件进行比较。我们将重新访问和重新采样我们的Cape Romain位置（沿着两个横断面的10个站点），以及测量我们的10个长期SET站点附近的Muddy Bay（在Cape Romain）。此外，还将占用至少其他四个沿着样带的地点，以确保与飓风有关的存款的广泛空间覆盖。将在每个站点采集沉积物岩心、浅地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个飓风“艾玛”（由环境沉积物引起的波浪和风暴潮）和飓风“佛罗伦萨”（引入新的河流沉积物）带来的沉积物。后者将通过观察、短沉积物岩心的沉积学分析（粒度、结构、物理结构、颜色）和与飓风“厄玛”和飓风“佛罗伦萨/迈克尔”相关的地表样本的大量地球化学分析（TOC、TN、delta 13 CTOC、delta 15 NTN）来完成。此外，我们将检查现有的SET记录，以确定它们是否捕获了过去与风暴相关的沉积峰值。来自NSF的资金支持20个表层沉积物样品的现场采样和实验室处理和地球化学分析（Irma和佛罗伦萨/迈克尔各10个），以及在新采样站收集的10个岩心的短岩心分析。该奖项反映了NSF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。