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Sediment Dynamics of a Divergent Bay–Marsh Complex
Estuaries and Coasts ( IF 2.7 ) Pub Date : 2020-11-17 , DOI: 10.1007/s12237-020-00855-5
Daniel J. Nowacki , Neil K. Ganju

Bay–marsh systems, composed of an embayment surrounded by fringing marsh incised by tidal channels, are widely distributed coastal environments. External sediment availability, marsh-edge erosion, and sea-level rise acting on such bay–marsh complexes may drive diverse sediment-flux regimes. These factors reinforce the ephemeral and dynamic nature of fringing marshes: material released by marsh-edge erosion becomes part of a bay–marsh exchange that fuels the geomorphic evolution of the coupled system. The dynamics of this sediment exchange determine the balance among seaward export, deposition on the embayment seabed, flux into tidal channels, and import to the marsh platform. In this work, we investigate the sediment dynamics of a transgressive bay–marsh complex and link them to larger-scale considerations of its geomorphic trajectory. Grand Bay, Alabama/Mississippi, is a shallow microtidal embayment surrounded by salt marshes with lateral erosion rates of up to 5 m year−1. We collected 6 months of oceanographic data at four moorings within Grand Bay and its tidal channels to assess hydrographic conditions and net sediment-flux patterns and augmented the observations with numerical modeling. The observations imply a divergent sedimentary system in which a majority of the suspended sediment is exported seaward, while a smaller fraction is imported landward via tidal channels, assisting in vertical marsh-plain accumulation, maintenance of channel and intertidal-flat morphologies, and landward transgression. These results describe a dynamic system that is responsive to episodic atmospheric forcing in the absence of a strong tidal signal and the presence of severe lateral marsh loss.



中文翻译:

海湾-沼泽发散复合体的泥沙动力学

海湾-沼泽系统由潮汐通道切割成的边缘沼泽包围的一个小海湾组成,是分布广泛的沿海环境。外部沉积物的可利用性,沼泽边缘的侵蚀以及海平面上升对这类海湾-沼泽复合体的影响可能会推动多种沉积物-通量的变化。这些因素增强了边缘沼泽的短暂性和动态性:沼泽边缘侵蚀释放的物质成为海湾-沼泽交换的一部分,为耦合系统的地貌演化提供了动力。这种沉积物交换的动力学决定了向海出口,在浮标海床上的沉积物,潮汐通量以及向沼泽平台的进口之间的平衡。在这项工作中,我们研究了海侵海湾-沼泽复合体的沉积动力学,并将其与地貌轨迹的更大范围的考虑联系起来。大湾区-1。我们在大湾及其潮汐通道内的四个系泊处收集了6个月的海洋学数据,以评估水文条件和净沉积物通量模式,并通过数值模拟扩大了观测范围。这些观测结果暗示了一个分散的沉积系统,其中大部分悬浮沉积物通过海流出口,而一小部分则通过潮汐通道向陆运输入,这有助于垂直平原沼泽堆积,维持河道和潮间带的形态以及向内海侵。 。这些结果描述了一个动态系统,该系统在没有强烈的潮汐信号和严重的横向沼泽损失的情况下,对大气的强迫做出响应。

更新日期:2020-11-17
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