Non-Linear Dynamics Determine the Long-term Fate of Salt Marshes

Sergio Fagherazzi

Dept. of Earth and Environment
Marine Program
Boston University

Friday, Feb. 9, 2018, 3:10pm
Chase 130

The potential of salt marshes to serve as natural buffers against violent storms seems even more important in view of significant threats imposed by climate change, such as increased
storminess and higher hurricane activity registered in the past decades. Unfortunately, Salt marsh losses have been documented worldwide because of land use change, wave erosion, and sea-level rise. Sea level rise is often viewed as the main driver of salt marsh deterioration. However, while salt marshes can reach equilibrium in the vertical direction, they are inherently unstable in the horizontal direction. Marsh expansion driven by sediment supply rarely matches lateral erosion by waves, creating a dynamic landscape. Recent results show that marsh collapse can occur in the absence of sea level rise if the rate at which sediment is eroded at marsh boundaries is higher than the input of sediment from nearby rivers or from the continental shelf. We propose that the horizontal dynamics and related sediment fluxes are key factors determining the survival of salt marshes. Only a complete sediment budget between salt marshes and nearby tidal flats can determine the fate of marshes at any given location, with sea level rise being only one among many external drivers. Moreover, salt marshes seem more susceptible to variations in mean wave energy rather than changes in the extremes. The intrinsic resistance of salt marshes to violent storms and their predictable erosion rates during moderate events should be taken into account by coastal managers in restoration projects and risk management plans.


Sergio Fagherazzi studies geomorphology, hydrology, and coastal and marine geology. His research is oriented in three main directions: the morphological modeling of the continental shelf—formation and evolution of riverine networks during sea-level lowstands and subsequent channel filling during high-stands; the study of the hydrodynamics and morphology of salt marshes—observation, understanding, and modeling of creeks and channels developing on a salt marsh surface; and the numerical study of equations characteristic of coastal processes and hydrology—a dynamic model linking phenomena occurring at different spatial scales. Dr. Fagherazzi earned his bachelor's and doctoral degrees at the University of Padua in Italy.