Contrasting saltmarsh vegetation impacts under increasing sea level rise rates

The resilience of saltmarshes mainly depends on their ability to gain elevation by sediment accretion to keep pace with sea level rise. While vegetation is known to facilitate sediment accretion at the plant scale by trapping mineral sediments and producing organic matter, the long-term impact at the landscape scale is still poorly understood. Here we use the biogeomorphic model Demeter to reveal contrasting vegetation impacts on spatial patterns of sediment accretion under different sea level rise regimes. Under contemporary sea level rise rates (2-10 mm/yr), vegetation inhibits sediment transport from tidal channels to platform interiors and creates levee-depression patterns. Hence, intertidal platforms accrete slower with vegetation than without, but this trend attenuates with increasing sea level rise rate, as water depth increases, and vegetation drag decreases. Under extreme sea level rise rate (20 mm/yr), platform interiors don’t keep up and turn into open water, while vegetation allows to preserve intertidal levees. Our results help to better understand some basic biophysical mechanisms that will control the fate of coastal wetlands under global climate change.