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，因为在浪涌淹没期间发生净沉积，或有害的，因为沼泽边缘的侵蚀和风暴波的地表挖掘。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湾盐沼中的这些范式。地点范围从佛罗里达到南卡罗莱纳沿纬度梯度增加的春季潮差（1.7-2.4米），背障沼泽宽度(5？7公里)，以及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和沉积物的可用性方面表现出变化，这将有助于限制这些因素在暴风雨期间向沼泽贡献沉积物方面的相对作用。了解沼泽沉积对低洼植被海岸带的所有管理者都很有意义。量化滨海湿地如何响应相对海平面上升而增加，以及风暴可能发挥的作用，对于模拟未来湿地的演变和对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，包括降低风暴潮高度和相关的社会经济成本，以及为鱼类提供苗圃，这项研究具有广泛的社会意义。当飓风“厄玛”沿着佛罗里达州西海岸移动时，风暴的风型和大小在东南海岸形成了强劲的陆上风，在南卡罗来纳产生了巨大的风暴潮。潮位计数据显示，佛州北部至南太平洋中部的沼泽被淹至1米深，并持续了约7至17小时。相关的风暴潮沉积物可能很大；它们的来源可能是当地的（沼泽或泻湖底）或内部大陆架。该项目将调查Irma风暴沉积物的性质（横向范围、厚度和来源）（与背景相比）。(1)浅沟（~20 cm）；(2)地表样品（已识别的Irma矿床）；(3)双短岩心（每个50厘米长，直径8厘米）沿着从屏障到大陆(5？6芯/样;共45个采样站)。我们还将绘制与厄玛有关的新的侵蚀特征、残骸线和植被破坏或掩埋。每个样带都有两个岩心，其中包含一个清晰的、具有代表性的Irma矿床，将对其进行短期放射性同位素（210Pb, 137Cs）取样，以提供多年代代性的吸积速率，并与事件沉积厚度进行比较。表面（Irma）沉积物和背景？通过分析总体生物地球化学特征（%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，以确定风暴和非风暴时期的来源差异（海洋、沼泽/泻湖、河流），还将使用两个吸积岩心深处的样本来检查事件沉积物的物源特征。

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.