潮滩前缘盐沼植被簇团与潮沟系统演变相互作用研究

Interaction between marginal salt marsh patches and tidal channel evolution on tidal flats

潮滩前缘盐沼植被簇团可以通过改变水动力及泥沙运动等过程影响潮沟系统的地形地貌,而潮沟系统的地形特征也会影响盐沼簇团的生长、扩张与侵蚀,但对盐沼簇团与潮沟系统地貌演变的相互作用机制尚缺乏认识。针对这一问题,本文构建了考虑盐沼植被动态演变的潮滩生物动力地貌耦合模型,模拟了盐沼植被簇团生长扩张与潮沟系统地貌演变过程,分析了不同初始数量的盐沼植被簇团与潮沟系统的空间格局及形态参数间的双向反馈。结果表明,潮沟先迅速向海陆两侧延伸,后发育出大量分汊;盐沼簇团向周边扩张后未被潮沟切割区域逐渐连成片。少量盐沼簇团能够增加潮沟密度,促进边缘冲刷式潮沟系统的发育。潮沟的走向受盐沼簇团分布位置及数量的影响,多个盐沼植被簇团间的水流集中比单个簇团的边缘水流冲刷更易形成潮沟。在盐沼植被簇团与潮沟系统共同发育初期,潮沟系统发育受盐沼植被簇团的促进作用较大,后期潮沟内比簇团边缘更易形成水流汇聚,盐沼簇团的影响逐渐由促进作用转为稳定作用。此外,潮沟的存在限制了盐沼植被的横向扩散,切割了盐沼植被簇团,影响盐沼植被的空间分布格局。本研究揭示了盐沼植被簇团与潮沟系统地貌耦合演化机制,可为盐沼潮滩生态系统保护修复提供科学依据。

Marginal salt marsh patches play a crucial role in the morphological evolution of salt marsh-tidal flat systems by dissipating hydrodynamics and stabilizing sediment,and the tidal channel can also influence the growth,expansion and erosion of the salt marsh patches.However,the interactions between saltmarsh patch expansion and tidal channel formation are complex and poorly understood.In the study,we established a two-dimensional biomorphodynamic model and introduced a dynamic vegetation module to simulate the spatial-temporal distribution of saltmarsh patches and the geomorphic evolution of the tidal channel system.We explored the two-way feedback between the spatial patterns of the tidal trench system and salt marsh vegetation patches with different initial numbers.Model results showed that the tidal channel extended rapidly to both sides of the sea and land at first,and then developed a large number of creeks,and the salt marsh patches expanded to the periphery and gradually formed a large patch.Besides,the presence of marsh patches can increase the density of tidal channels and promote the development of tidal channels.Further,the orientation of tidal channels was affected by the spatial distribution of marsh patches,which can divert water flow and induce the concentration of tidal flow.Specially,in the early stage of saltmarsh evolution,more tidal channels were formed by the interactions between hydrodynamics and sediment motion with the increase of marsh patch numbers,and in the later stage,the influence of salt marsh clusters gradually changed from promotion to stabilization.However,the expansion and the spatial distribution pattern of salt marsh patches was later limited by the formation of tidal channels reciprocally.Our study extended current understanding of the mechanisms underlying the co-evolution of marsh patches and tidal channels,and can provide scientific basis for future works on coastal protection and restoration.