RAPID: Collaborative Research: Storm Surge Deposition on Salt Marshes: Impacts of Hurricane Irma from Florida to South Carolina

RAPID：合作研究：盐沼上的风暴潮沉积：飓风艾尔玛从佛罗里达州到南卡罗来纳州的影响

• 批准号: 1800825
• 负责人: Christopher Hein
• 金额: $ 0.45万
• 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: 2017
• 资助国家: 美国
• 起止时间: 2017-11-15 至 2018-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1800825&HistoricalAwards=false
• 关键词: RAPID; Collaborative; Research; Storm; Surge

Scientists continue to weigh the net impact of hurricanes on wetlands. These events may be considered beneficial because of net sedimentation that occurs during surge inundation, or detrimental due to erosion of the marsh edge and surface excavation by storm waves. This study will exploit the new sedimentologic record left by Hurricane Irma to examine these paradigms in the salt marshes of the South Atlantic Bight. Sites range from Florida to South Carolina along a latitudinal gradient of increasing spring tidal range (1.7-2.4 m), backbarrier marsh width (5?7 km), and flow-weighted average suspended sediment concentrations in nearby rivers (13?27 mg/l). They exhibit variations in physical characteristics, proximity to fluvial source, and sediment availability that will help constrain the relative role of these factors in contributing sediment to marshes during storms. Understanding marsh sedimentation is of interest to all stewards of low-lying vegetated coastal zones. Quantifying how coastal wetlands accrete in response to relative sea-level rise, and the contributions that storms may play, is paramount to modeling future wetland evolution and long-term resilience to storm impacts. This study has broad societal implications given the recognized importance of the ecosystem services provided by salt marshes, including reducing storm surge height and related socioeconomic costs, and providing nurseries for fish stocks. While Hurricane Irma tracked over the west coast of Florida, the wind patterns and size of the storm created strong onshore winds along the southeast coast, producing a large stormsurge up into South Carolina. Tide gauge data indicate that marshes from northern FL to central SC were flooded to a depth of 1 m, and remained so for ~7 to 17 hrs. Associated storm surge deposits are likely to be significant; their source may be local (marshes or lagoon floor) or from the inner shelf. The project will investigate the nature (lateral extent, thickness, and provenance) of Irma storm deposits (compared to ?background? sedimentation) through the analysis of (1) shallow trenches (~20 cm); (2) surface samples (of identified Irma deposits); and (3) double short cores (each 50-cm long, 8 cm in diameter) collected along two transects at each site from the backbarrier to mainland (5?6 cores/transect; ~45 sampling stations total). We will also map new erosional features, wrack lines, and vegetation damage or burial, related to Irma. Two cores from each transect containing a clear, representative Irma deposit will be sampled for short-lived radioisotope (210Pb, 137Cs) to provide multi-decadal accretion rates for comparison with event-sedimentation thicknesses. Surface (Irma) deposits and ?background? samples from depth in the two accretion cores, will also be used to examine event-sediment provenance signatures through analysis of bulk biogeochemical characteristics (%TOC, C:N, ä13CTOC, ä15NTN), and assemblages of diatoms and organic biomarkers adsorbed to/co-deposited with these sediments to determine source differences (marine, marsh/lagoon, fluvial) between storm and non-storm periods.

科学家们继续权衡飓风对湿地的净影响。这些事件可能被认为是有益的，因为在洪水淹没期间发生的净沉积，或者是有害的，因为风暴波对沼泽边缘的侵蚀和地表开挖。这项研究将利用飓风艾尔玛留下的新沉积学记录来检验南大西洋湾盐沼中的这些范例。地点范围从佛罗里达州到南卡罗来纳州，沿纬度梯度增加，春潮差（1.7-2.4 m）、后障沼泽宽度（5?7 km）和附近河流的流量加权平均悬浮沉积物浓度（13?27 mg/l）。它们在物理特征、与河流源头的接近程度以及沉积物可用性方面表现出变化，这将有助于限制这些因素在风暴期间向沼泽贡献沉积物的相对作用。了解沼泽沉积是所有低洼植被沿海地区管理者都感兴趣的。量化沿海湿地如何随着相对海平面上升而增长，以及风暴可能发挥的作用，对于模拟未来湿地的演变和风暴影响的长期恢复能力至关重要。鉴于盐沼提供的生态系统服务的重要性已得到公认，包括降低风暴潮高度和相关的社会经济成本，以及为鱼类种群提供苗圃，这项研究具有广泛的社会影响。当飓风“艾尔玛”席卷佛罗里达州西海岸时，风暴的风型和规模在东南海岸产生了强烈的陆上风，并在南卡罗来纳州产生了巨大的风暴潮。潮汐计数据表明，从佛罗里达州北部到南卡罗来纳州中部的沼泽被淹没至 1 m 深度，并持续约 7 至 17 小时。相关风暴潮沉积物可能数量巨大；它们的来源可能是当地的（沼泽或泻湖底部）或来自内陆架。该项目将通过分析 (1) 浅沟（约 20 厘米）来调查艾尔玛风暴沉积物的性质（横向范围、厚度和来源）（与“背景”沉积物相比）； (2) 表面样本（已识别的艾尔玛矿床）； (3) 双短岩心（每个长 50 厘米，直径 8 厘米），从后屏障到大陆，沿着每个地点的两条样线收集（5?6 个岩心/样线；总共约 45 个采样站）。我们还将绘制与艾玛相关的新侵蚀特征、残骸线以及植被破坏或掩埋图。每个横断面的两个岩心含有清晰的、具有代表性的 Irma 沉积物，将对短寿命放射性同位素（210Pb、137Cs）进行采样，以提供数十年的增生率，以便与事件沉积厚度进行比较。表面（艾玛）沉积物和“背景”？两个增生核心深度的样本也将用于通过分析大量生物地球化学特征（%TOC、C:N、ä13CTOC、ä15NTN）以及吸附到/与这些沉积物共同沉积的硅藻和有机生物标记物的组合来检查事件沉积物来源特征，以确定沉积物之间的来源差异（海洋、沼泽/泻湖、河流） 风暴期和非风暴期。