Elevation Trajectories of US Atlantic Coast Marshes: Insights from SET-MH Monitoring

This research assesses the vertical resilience of tidal marshes along the U.S. Atlantic Coast using records from Surface Elevation Tables (SET) and Marker Horizons (MH), collected across an extensive monitoring network. We compiled SET-MH data from 564 stations across 21 coastal regions, encompassing diverse geomorphic settings and spanning up to two decades of observations. From this compilation, a subset of 308 stations was selected based on the availability of both surface elevation change (SEC) and vertical accretion (VA) data with minimum temporal coverage to calculate SEC and VA rates. Shallow subsidence (SS) was calculated (SS = VA − SEC), providing insights into subsurface processes influencing marsh elevation trajectories. The analysis revealed a broad spectrum of marsh behaviors, with an approximately equal number of sites exhibiting an elevation surplus or deficit, and a smaller proportion showing near-equilibrium conditions. These patterns indicate that while shallow subsidence remains a common limitation, its impact is frequently offset by root zone expansion or other biophysical processes. Spatial trends revealed regional clustering of elevation deficits in Georgia and Florida, contrasted by greater resilience in northeastern regions such as Massachusetts and Maine. Marshes in New Jersey exhibited pronounced spatial variability. This heterogeneity hints at site-specific factors including tidal regime and vegetation structure (high or low marsh). Ongoing work includes classifying marsh types and integrating relative sea-level data from nearby tide gauges to determine vulnerability to sea-level change. Together, these efforts will contribute to a more robust understanding of long-term vertical trajectories of marshes on the Atlantic seaboard.