Dynamic response of marshes to perturbations in suspended sediment concentrations and rates of relative sea level rise

We have developed an analytical model of salt marsh evolution that captures the dynamic response of marshes to perturbations in suspended sediment concentrations, plant productivity, and the rate of relative sea level rise (RSLR). Sediment-rich and highly productive marshes will approach a new equilibrium state in response to a step change in the rate of RSLR faster than sediment-poor or less productive marshes. Microtidal marshes will respond more quickly to a step change in the rate of RSLR than mesotidal or macrotidal marshes. Marshes are more resilient to a decrease rather than to an increase in the rate of RSLR, and they are more resilient to a decrease rather than to an increase in sediment availability. Moreover, macrotidal marshes are more resilient to changes in the rate of RSLR than their microtidal counterparts. Finally, we find that a marsh's ability to record sea level fluctuations in its stratigraphy is fundamentally related to a timescale we call T-FT, or filling timescale, which is equal to the tidal amplitude divided by the maximum possible accretion rate on the marsh (a function of plant productivity, sediment properties, and availability). Marshes with a short-filling timescale (i.e., marshes with rapid sedimentation or small tidal amplitudes) are best suited to recording high-frequency fluctuations in RSLR, but our model suggests it is unlikely that marshes will be able to record fluctuations occurring over timescales that are shorter than decadal.