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首页> 外文期刊>Estuarine Coastal and Shelf Science >Hydrodynamic forcing on salt-marsh development: Distinguishing the relative importance of waves and tidal flows
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Hydrodynamic forcing on salt-marsh development: Distinguishing the relative importance of waves and tidal flows

机译：盐沼发育的水动力强迫：区分波浪和潮汐流的相对重要性

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To unravel the relation between hydrodynamic forcing and the dynamics of the tidal flat-salt-marsh ecosystem, we compared hydrodynamic forcing in terms of proxies relevant to bed sediment motion for four tidal flat-salt-marsh ecosystems that were contrasting in terms of wind exposure (sheltered vs. exposed) and lateral development (shrinking vs. expanding). Wave and current field measurements on these four contrasting tidal flat and salt-marsh ecosystems indicated that the hydrodynamic forcing on the bottom sediment (bed shear stress) was strongly influenced by wind-generated waves, more so than by tidal- or wind-drive currents. The measurements further showed that the hydrodynamic forcing decreased considerably landward of the marsh cliff, highlighting a transition from vigorous (tidal flat and pioneer zone) to sluggish (mature marsh) fluid forcing. Spatial wave modeling using measured wind, revealed that the time-integrated wave forcing on the intertidal mudflat in front of the marsh (i.e., the potential bed sediment pickup) was a factor two higher for salt marshes that are laterally shrinking than for laterally expanding marshes, regardless of whether these marshes were exposed to or sheltered from the wind. The same result could not be obtained from a straightforward wind speed and fetch length approach for estimating wave forcing. This confirmed that wave force estimates required spatial modeling to be consistent with the sites trends of shrinking or expanding marshes and wind exposure is not enough to characterize the wave forcing at these sites.rnSeasonal changes in wave forcing identified from wind measurements potentially provide an alternative mechanism for marsh cliff formation. During the calm summer, fine sediments switches from the water column to the bed. During the following winter, fine sediment is retained within the vegetated regions while being returned to the water column from the bare tidal flats. The continuous slow upward growth of vegetated areas combined with the seasonal cyclic tidal flat elevations, could, during winter, cause a discontinuity at the bare/vegetated boundary. If this discontinuity grows large enough for plant die-off to occur, then a small cliff will form.
机译：为了揭示水动力强迫与潮汐平盐沼生态系统动力学之间的关系，我们比较了与四个受潮风形成对比的潮汐平盐沼生态系统与床底泥沙运动相关的水动力强迫。 （避开与暴露）和横向展开（缩小与扩展）。在这四个形成对比的潮滩和盐沼​​生态系统中进行的波场和流场测量表明，底部沉积物的水动力强迫（床切应力）受风浪的影响很大，而不是受潮汐或风力驱动的影响更大。 。测量结果进一步表明，水动力强迫在沼泽悬崖的陆地上显着减少，突显了从剧烈的（潮滩和先驱带）到缓慢的（成熟的沼泽）流体强迫的过渡。使用实测风进行的空间波建模显示，在沼泽前的潮间带滩涂上的时间积分波（即潜在的床沉积物吸收）是横向收缩的盐沼比横向扩展的沼泽高两倍。 ，无论这些沼泽是否暴露在风中或被风挡住。从直接的风速和获取长度方法估算波浪强迫无法获得相同的结果。这证实了波浪力的估计需要进行空间建模，以使其与沼泽地不断缩小或扩大的趋势相一致，并且风的暴露不足以表征这些地点的波浪强迫.rn从风速测量中识别出的波浪强迫的季节性变化可能提供了另一种机制沼泽悬崖形成。在平静的夏季，细小的沉积物从水柱转移到床层。在接下来的冬天，细小的沉积物被保留在植被区域内，同时又从裸露的潮汐带回到水柱。植被区域持续缓慢的向上增长，加上季节性的潮汐平坦高程，可能在冬季导致裸露/植被边界不连续。如果这种不连续性增大到足以使植物死亡的程度，那么就会形成一个小悬崖。

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