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

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，因为在潮汐淹没期间发生了净沉积，或者由于沼泽边缘的侵蚀和暴风浪对地表的开挖而被认为是有害的。这项研究将利用飓风伊尔玛留下的新的沉积学记录来检验南大西洋海湾盐沼中的这些范例。站点范围从佛罗里达到南卡罗来纳州，沿纬度梯度递增春潮差(1.7m~2.4m)、后障沼泽宽度(5.7 km)和附近河流的水流加权平均悬浮泥沙浓度(13.27 mg/L)。它们在物理特征、与河流源头的接近程度和沉积物可获得性方面表现出差异，这将有助于限制这些因素在风暴期间为沼泽贡献沉积物的相对作用。了解沼泽沉积对低洼植被繁茂的沿海地带的所有管理人员都很有兴趣。量化沿海湿地如何对相对海平面上升作出反应，以及风暴可能起到的作用，对于模拟未来湿地演变和对风暴影响的长期复原力至关重要。这项研究具有广泛的社会影响，因为人们认识到盐沼提供的生态系统服务的重要性，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。当飓风伊尔玛在佛罗里达州西海岸肆虐时，风暴的风型和大小在东南海岸造成了强烈的陆上大风，并在南卡罗来纳州产生了巨大的风暴潮。验潮仪数据显示，从佛罗里达北部到南加州中部的沼泽被淹没到1米深，并持续了约7至17小时。相关的风暴潮沉积可能很重要；它们的来源可能是当地(沼泽或泻湖底部)或来自内陆架。该项目将调查伊尔玛风暴沉积的性质(横向范围、厚度和物源)(与背景相比较？通过分析(1)浅海沟(~20厘米)，(2)地表样品(已识别的Irma矿床)，以及(3)沿从后屏障到大陆的每个地点的两个横断面采集的双短岩芯(每个长50厘米，直径8厘米)(5？6个岩芯/断面；总共约45个采样站)进行分析。我们还将绘制与伊尔玛相关的新的侵蚀地貌、珊瑚线和植被破坏或掩埋。每个断面的两个岩芯都包含一个清晰的、具有代表性的Irma矿床，将对其进行短期放射性同位素(210Pb、137Cs)采样，以提供数十年的吸积率，以便与事件沉积厚度进行比较。地表(IRMA)矿床和背景？来自两个吸积岩芯深度的样品也将被用来通过分析大量生物地球化学特征(%TOC，C：N，ä13CTOC，ä15NTN)以及吸附在这些沉积物上/与这些沉积物共同沉积的硅藻和有机生物标志物的组合来检查事件-沉积物来源特征，以确定风暴和非风暴期间的来源差异(海洋、沼泽/泻湖、河流)。

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.