Salt marshes and mangrove forests provide critical ecosystem services such as reduced sediment erosion and increased hydrodynamic buffering. Sediment transport and hydrodynamics can be influenced by specific functional traits of the plants (for example, flexibility vs. rigidity) and community traits (for example, spatial density). While there is a growing body of literature on plant trait and hydrodynamic interactions, direct comparative studies of sediment transport and scour development in and around intertidal wetland edges are scarce. In this study we systematically compared the effects of plant traits on sediment budgets around the lateral edges of intertidal wetlands under controlled hydrodynamic and sedimentary conditions using full scale vegetation mimics with contrasting flexibilities and densities. Experiments were carried out in a large-scale flume, using two spatial densities each of flexible and rigid vegetation mimics. We measured unconsolidated sedimentary bed-level changes in experimental runs using waves only, currents only, and waves combined with currents. Both mimic types dampened the energy of the incoming flow, highlighting the role of rigid and flexible aquatic vegetation in providing coastal protection. The rigid vegetation mimics’ lateral edge experienced larger velocities, more energetic turbulence, and local scour around individual stems. Scour around stems could influence the lateral expansion of the rigid vegetation ecosystem by reducing sediment stability and thus decreasing seedling establishment success. The flexible plant mimics produced lower turbulence at their leading edge, which resulted in sediment being deposited over a shorter distance into the patch than in the rigid mimics. Decreased vegetation density caused reduced sediment erosion at the leading edge and less sediment accumulation within the vegetation patches for both the rigid and flexible mimics. The hydrodynamic and sedimentary processes identified for both ecosystems are linked to different feedbacks. A positive feedback was identified in which vegetation attenuates hydrodynamic energy allowing sediment accumulation within the patch. A negative feedback was identified where large velocities caused flow divergence and erosion outside of the vegetation, and would therefore compromise its lateral expansion. High densities of rigid vegetation enhance this negative feedback. Lower density flexible vegetation, however, combined with less energetic hydrodynamic conditions facilitate the expansion of vegetation patches as they cause less flow divergence and therefore less erosion. The strong flow divergence observed in the rigid vegetation cases highlight their importance for buffering hydrodynamics but at the cost of increased erosion within the front end of patches and along their lateral edges.

盐沼和红树林提供重要的生态系统服务，例如减少沉积物侵蚀和增加水动力缓冲。沉积物运输和流体动力学可能受植物的特定功能特征（例如，柔韧性与刚性）和群落特征（例如，空间密度）的影响。虽然关于植物性状和水动力相互作用的文献越来越多，但对潮间带湿地边缘及其周围的沉积物迁移和冲刷发展的直接比较研究却很少。在这项研究中，我们系统地比较了植物性状对受控水动力和沉积条件下潮间带湿地侧缘周围沉积物预算的影响，使用具有对比灵活性和密度的全尺寸植被模拟物。实验是在一个大型水槽中进行的，使用了两种空间密度，每种都有柔性和刚性的植被模拟物。我们仅使用波浪、仅使用水流和波浪与水流结合来测量实验运行中松散沉积床层的变化。两种模拟类型都抑制了流入水流的能量，突出了刚性和柔性水生植被在提供海岸保护方面的作用。刚性植被模拟物的横向边缘经历了更大的速度，更有活力的湍流，以及单个茎周围的局部冲刷。茎周围的冲刷可以通过降低沉积物稳定性来影响刚性植被生态系统的横向扩展，从而降低幼苗建立的成功率。灵活的植物模拟物在其前沿产生较低的湍流，这导致沉积物以比刚性模拟物更短的距离沉积到斑块中。对于刚性和柔性模拟物，植被密度降低导致前缘沉积物侵蚀减少，植被斑块内沉积物积累减少。为这两个生态系统确定的水动力和沉积过程与不同的反馈有关。确定了一个正反馈，其中植被减弱了水动力能量，从而允许沉积物在斑块内堆积。当大速度导致植被外的流动发散和侵蚀时，确定了负反馈，因此会损害其横向扩展。高密度的刚性植被增强了这种负反馈。然而，密度较低的柔性植被，再加上能量较低的水动力条件，有助于植被斑块的扩张，因为它们导致较少的流动发散，因此较少的侵蚀。在刚性植被案例中观察到的强烈流动分歧突出了它们对缓冲流体动力学的重要性，但代价是斑块前端和沿其横向边缘的侵蚀增加。