Vegetation Does Not Control Suspended Sediment Deposition in Salt Marshes

Intertidal marshes are valuable geophysical systems, but their extent is rapidly declining globally. Marshes tend to keep up with sea-level rise through suspended-sediment and organic-matter deposition, up to a marsh-specific threshold rate of sea-level rise. Studies that explore marsh survival often assume that inorganic sediment deposition rates are directly linked to the density of marsh vegetation---coupling the inorganic and organic deposition processes. Here we examine the fluid-dynamics regulating sediment transport across a vegetated marsh and derive a framework for platform-wide sediment deposition. We demonstrate that sediment deposition rates are largely independent of vegetation density due to quasi-steady tidal propagation and vegetation-generated turbulence. Consequently, sediment deposition rates are primarily controlled by marsh size and tidal properties. Supported by extensive observations, these findings simplify modeling of long-term marsh dynamics by decoupling inorganic and organic deposition and offer insights into the processes that determine marsh resilience to accelerating sea-level rise.