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Role of mudflat-creek sediment exchanges in intertidal sedimentary processes
Journal of Hydrology ( IF 6.4 ) Pub Date : 2018-12-01 , DOI: 10.1016/j.jhydrol.2018.10.027
Weiming Xie , Qing He , Xianye Wang , Leicheng Guo , Keqi Zhang

Abstract Intertidal environments, including bare mudflats, tidal creeks, and vegetated salt marshes, are of significant physical and ecological importance in estuaries. Their morphodynamics are closely linked by mudflats and creek networks. Understanding water motion and sediment transport in mudflats and tidal creeks is fundamental to understand intertidal morphodynamics in intertidal environments. To explore dynamic interactions between tidal creeks and mudflats, we conducted field campaigns monitoring water depths, tidal currents, waves, suspended sediments, and bed-level changes at sites in both mudflats and tidal creeks in the Eastern Chongming tidal wetland in the Yangtze Delta for a full spring-neap tidal cycle. We saw that under fair weather conditions, the bed-level changes of the tidal creek site displayed a contrary trend compared with those of the mudflat site, indicating the source-sink relationship between tidal creek and mudflat. During over-marsh tides, the tidal creek site with relatively high bed shear stresses (averagely, 0.37 N/m2) was eroded by 35 mm whereas the mudflat site was accreted by 29 mm under low bed shear stresses (averagely, 0.18 N/m2). To the contrast, during creek-restricted tides, deposition occurred in the tidal creek site by 20 mm under low bed shear stresses (averagely, 0.09 N/m2) whereas erosion occurred in the mudflat site by 25 mm under relatively high bed shear stresses (averagely, 0.21 N/m2). Over a spring-neap tidal cycle, the net bed level changes were −15 mm (erosion) and 4 mm (deposition) in tidal creeks and mudflats, respectively. These results suggested that there were alternated erosion-deposition patterns in spring and neap tides, and a sediment source and sink shift between mudflats and creeks. We found that the eroded sediments in mudflats were transported landward into tidal creeks and deposited therein in neap tides, and these newly deposited sediments would be resuspended and transported to surrounding marshes (over-marsh deposition) at spring tides. The coherent sediment transport and associated erosion-deposition pattern within the mudflat-creek system at spring-neap tidal time scales thus played a fundamental role in intertidal morphodynamic development. These findings suggest that management and restoration of intertidal ecosystem need to take the entire mudflat-creek-marsh system as a unit into consideration rather than focusing on single elements.

中文翻译:

泥滩-溪流沉积交换在潮间带沉积过程中的作用

摘要 潮间带环境,包括裸露的泥滩、潮汐小溪和植被盐沼,在河口具有重要的物理和生态重要性。它们的形态动力学与泥滩和小溪网络密切相关。了解泥滩和潮汐小溪中的水运动和沉积物输送是了解潮间带环境中潮间带形态动力学的基础。为了探索潮汐小溪和泥滩之间的动态相互作用,我们在长江三角洲崇明东部潮汐湿地的泥滩和潮汐小溪中进行了现场监测,监测了水深、潮流、波浪、悬浮沉积物和床位变化。一个完整的春季潮汐周期。我们看到在晴朗的天气条件下,潮溪地床位变化与泥滩地床位变化趋势相反,表明潮溪地与泥滩地存在源汇关系。在沼泽潮汐期间,具有较高河床剪应力(平均为 0.37 N/m2)的潮汐小溪场地被侵蚀了 35 mm,而在低河床剪应力(平均为 0.18 N/m2)下,泥滩场地增加了 29 mm )。相比之下,在小溪限潮期间,在低床剪切应力(平均为 0.09 N/m2)下,潮汐小溪场地发生了 20 mm 的沉积,而在相对较高的床剪切应力下,泥滩场地发生了 25 mm 的侵蚀(平均为 0.21 N/m2)。在春季小潮周期内,潮汐小溪和泥滩的净床水位变化分别为 -15 毫米(侵蚀)和 4 毫米(沉积)。这些结果表明,春季和小潮期间存在交替的侵蚀沉积模式,泥滩和小溪之间存在沉积物源汇转移。我们发现,泥滩中被侵蚀的沉积物在小潮时向内输送到潮汐小溪并沉积在那里,这些新沉积的沉积物在大潮时会重新悬浮并输送到周围的沼泽(沼泽沉积)。因此,在春季-小潮时间尺度上泥滩-小溪系统内的连贯沉积物运输和相关的侵蚀沉积模式在潮间带形态动力学发展中发挥了重要作用。这些研究结果表明,潮间带生态系统的管理和恢复需​​要将整个泥滩-溪-沼系统作为一个单元来考虑,而不是只关注单个元素。
更新日期:2018-12-01
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