A multi-scale comparison of elevation measurement methods in northeastern tidal marshes of the United States

Coastal ecosystems are at risk across the globe due to combined effects of sea-level rise and human development. This threat is prevalent in the northeastern USA, where sea levels increase 2-6 mm annually. Much of this coastline is buffered by tidal marsh, directly linking monitoring of this ecosystem to effective coastal management into the future. We estimated local and regional elevations of tidal marshes from Maine to Virginia using real-time kinematic (RTK) technology, unmanned aircraft system (UAS) technology, and regional datasets from the National Elevation Dataset (NED) to evaluate elevation monitoring methods for coastal marshes. Locally we found that RTK-sourced elevation measurements are predicted well using the 1/9 arc-second NED layer, however UAS-derived DSMs did not predict RTK values well. Regionally we found the 1/9 arc-second NED explained 90% of the variation in RTK measurements, and this relationship was strongest in high marsh and terrestrial border across spatial scales. Additionally, we found that elevation increases from south to north in the majority of marsh cover types, indicating that continent-scale mechanisms may determine elevation relative to mean sea level. We suggest further work using UAS-sourced Digital Terrain Models and the NED as an economical substitute for RTK in higher-elevation cover types.