Dense Vegetation Hinders Sediment Transport Towards Saltmarsh Interiors

The resilience of saltmarshes mainly depends on their ability to gain elevation by sediment accretion to keep pace with sea level rise, and tidal channels play a crucial role in the supply of sediments towards their interiors. While feedbacks between vegetation and geomorphology are increasingly recognized as key drivers shaping a variety of tidal channel network structures, the resulting impact on long-term sediment accretion over the vegetated platforms remains poorly studied. At the plant-scale, vegetation facilitates sediment accretion by trapping mineral sediments and producing organic matter. At the landscape-scale, vegetation promotes the formation of dense, branching, and meandering tidal channel networks, which reduce the distance between saltmarsh interiors and their source of suspended sediments. In this presentation, we use a biogeomorphic model validated against data to reveal two mechanisms by which vegetation also hinders sediment transport towards saltmarsh interiors. First, vegetation concentrates tidal flow and sediment transport inside channels, which reduces sediment availability for deposition on saltmarsh platforms. Secondly, vegetation enhances sediment deposition close to channels, which deprives saltmarsh interiors of suspended sediments, creating levee-depression patterns and leading to pond formation. In the present context of accelerating sea level rise and human-induced decrease of sediment supply, our findings suggest that saltmarshes are more vulnerable than previously thought.

Abstract of an Oral Presentation or a Poster

AGU Fall Meeting, 12-16 December, Chicago, IL, USA