RAPID: Evolution of critical shear stress in the seabed of an urbanized estuary and natural estuary after the passage of Hurricane Ian

沿海水域中的许多污染物会附着在细小的沉积物上。为了预测与沉积物相关的污染物是如何输送的，有必要知道沉积物是如何移动的。海浪和海流的摩擦力是使表层沉积物重新悬浮所必需的，这是沉积物迁移的一个关键因素。所需摩擦力的大小取决于沉积物颗粒的大小和床表面的生物过程。藻垫和细菌薄膜会使沉积物更难重新悬浮。然而，飓风等强烈的身体干扰会破坏垫子，使再悬浮变得更容易。该项目将研究受飓风伊恩影响的佛罗里达海岸沉积物。时间序列样本将显示沉积物床对再悬浮的敏感性在一年中是如何演变的。这将使人们能够更好地预测强风暴后沉积物和与沉积物相关的污染物被输送到哪里。这项研究还将研究被红树林边缘包围的未开发区域和以海堤为边界的已开发区域之间的海床演变差异。先前的研究表明，红树林可以捕获细小的沉积物。被红树林包围的海湾比没有红树林的发达地区的海湾有更大的沉积物颗粒。发达海湾中的细粒沉积物更容易再悬浮。这可以加强与沉积物相关的污染物的移动，而飓风已被证明可以动员与沉积物相关的重金属。这项研究将有助于预测污染物是否可能被困在或从遭受大风暴袭击的地区转移出去，从而产生更广泛的影响。这项研究还将为沿海开发选择在水边实施红树林边缘提供信息。这是及时的，因为佛罗里达州西南部海岸附近的许多房屋被摧毁，很快就会恢复。了解海床的临界剪应力对于预测泥沙和与泥沙有关的污染物的迁移是必要的。这一点尤其重要，但在暴风雨对床造成强烈干扰后，这一点还没有得到很好的研究。这项拟议的研究评估了飓风伊恩过后佛罗里达州西南部两个沿海海湾海床的临界剪应力的演变。临界剪应力不仅取决于沉积物的大小，还取决于藻席和细菌生物膜生产与生物扰动的相反作用。快速反应是至关重要的，因为生物发展也可能是快速的，如果不尽快测量，飓风的影响将会消失。这项研究将比较一个经过广泛开发的沿海海湾的海床演变有何不同，包括用坚硬的稳定结构取代边缘红树林，与附近但未开发的海湾没有人类开发的海湾。这项研究将每季度在两个地点的三个重复岩芯上使用阵风侵蚀室测量临界应力。生物扰动量也将每季度进行评估，使用每个地点的三重岩芯和铍-7剖面的X光照片。据推测，临界切应力最初将随着细菌和藻类薄膜的发展而增加，然后随着大型动物在底栖生物中的重建而减少。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Many contaminants in coastal waters adhere to fine sediments. To predict how sediment-associated contaminants are transported it is necessary to know how the sediment moves. The amount of friction by waves and currents that is necessary to resuspend surface sediments is a key factor for sediment transport. The amount of friction needed depends on the size of the sediment grains and on biological processes at the surface of the bed. Algal mats and bacterial films can make it harder to resuspend sediment. However, a strong physical disturbance such as a hurricane can break down the mats and make resuspension easier. This project will study Florida coastal sediments impacted by Hurricane Ian. Time series samples will show how the sediment bed susceptibility to resuspension evolves over the course of a year. This will enable improved predictions about where sediment and sediment-associated contaminants are transported after strong storms. The study also will examine the difference in the evolution of the bed between an undeveloped area surrounded by a mangrove fringe and a developed area that is bordered by seawalls. Prior studies suggest that mangroves trap fine sediments. Bays surrounded by mangroves have larger sediment grains than bays in developed areas without mangroves. The fine sediments in developed bays are more easily available for resuspension. This can enhance the movement of sediment-associated contaminants, and hurricanes have been shown to mobilize sediment-associated heavy metals. This study will have broader impacts by helping predict whether contaminants are likely to be trapped or transported away from regions that are struck by large storms. The study also will inform coastal development choices regarding implementation of mangrove fringes at the water’s edge. This is timely since many homes were destroyed near the southwest Florida coast and will soon be restored. Understanding the critical shear stress of the seabed is necessary to predict the transport of sediment and sediment-associated contaminants. This is especially important, but not well studied, after intense disturbance to the bed caused by storms. The proposed research assesses the evolution of the critical shear stress of the seabed in two coastal bays in southwest Florida after the passage of Hurricane Ian. The critical shear stress depends not only upon the size of the sediment, but the opposing effects of algal mat and bacterial biofilm production versus bioturbation. A rapid response is essential because the biological development may also be rapid, and the effect of the hurricane will be lost if not measured soon. The study will compare how the evolution of the bed differs in a coastal bay that has had extensive development, including the replacement of fringe mangroves with hard stabilization structures, with a nearby but undeveloped bay with no anthropogenic development. The study will measure the critical stress using a Gust erosion chamber on three replicate cores from each of the two sites on a quarterly basis. The amount of bioturbation will be assessed quarterly as well, using X-radiographs of triplicate cores at each site and beryllium-7 profiles. It is hypothesized that the critical shear stress will initially increase as bacterial and algal films develop, then decrease as macrofauna reestablish within the benthos.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.