Spatial and Temporal Drivers of Coastal Wetland Formation and Persistence

Abstract

Coastal wetlands are complex biogeomorphic systems that provide important ecosystem services, but our current understanding of salt marsh evolution and persistence is based on models and empirical studies of limited spatial and temporal extent. In this dissertation, I ask: How and why do coastal wetlands form and persist? Using a geospatial framework of publicly available datasets, I analyzed drivers of wetland extent along the Atlantic and Gulf coasts of the United States. Results establish that distinct modes of wetland extent (fringing and basin full wetland extent) occur at spatial scales (approximately 10^0 to 10^2 km^2) predicted by theoretical models of local feedbacks among fetch, wind erosion, and marsh building. Marsh distributions reflect interactions between these local biogeomorphic feedbacks and macroscale drivers that set boundary conditions, including estuarine-scale morphology that governs wave energy, and riverine influence affecting sediment availability and transport. These relationships varied among regions by a regionally characteristic set of factors: estuary shape complexity, depth, estuary area and relative dominance of riverine to estuary volume. Using new and existing sediment cores from tidal marshes along the Atlantic and Gulf coasts, I analyzed the timing and spatial variability of wetland formation. Although most cores formed after the stabilization of sea level subsequent to the last ice age (approximately 4000 to 6000 ybp), overwash events, connection to major riverine systems, riverine morphology and timing of peak agriculture post European settlement all created spatial and temporal variability in the age of marshes. Historic sea level rise studies dominated the literature found for this study, pointing to the need for targeted investigations of drivers of tidal marsh formation. By reimagining tidal marshes in a macroscale framework, I investigated both the spatial and temporal drivers of land-water linkages and coastal wetland formation and persistence, elucidating ultimate drivers and future impacts on coastal wetlands from environmental pressures.