Coastal marsh resilience: a study on the role of bio-geomorphic self-organization

Tidal marshes are valuable coastal ecosystems that are threatened by global climate warming and the resulting sea level rise. Whether they drown or continue to exist, depends on the trapping of sediments that builds up the land surface. Tidal channel networks, which typically occur within tidal marshes, are the major supply routes for sediments towards the marshes and hence are expected to affect the capacity of marshes to keep up with sea level rise by sediment trapping. The development and evolution of tidal channel networks and the sediment trapping are locally determined by so-called bio-geomorphic interactions between plants, water flow and sediment transport. However, the effect of different environmental variables on channel network formation remains poorly understood. In this research, we investigated the impact of spatio-temporal plant colonization patterns by means of flume experiments. Four scaled landscape scale experiments were conducted in the Metronome tidal facility, a unique flume that tilts periodically to generate tidal currents. Two control experiments without vegetation, a third experiment with a channel-fringing vegetation colonization pattern, and a fourth with patchy vegetation colonization pattern. Seeds were distributed by water in the channel-fringing experiment, while a manual sowing method was used to obtain laterally expanding circular patches in the patchy experiment. Our results show that vegetation and their respective colonization pattern affect channel network formation both on a landscape scale and local scale. More extensive and effective channel networks are found in vegetation experiments. These results indicate that channel-fringing or patchy recruitment strategies might produce landscapes that are more resilient to sea level rise.