Tidal marshes are a major ecological resource in Virginia and a driver of many estuarine functions. Therefore, the long term sustainability of tidal marsh ecosystems is a question of great interest in the research community. Sea level is rising at an unusually high rate in the Chesapeake Bay relative to most of the Atlantic coastline, putting Bay marshes at high risk from drowning and erosion. Sea level rise-driven salinity changes communities and alters ecosystem services. Understanding the patterns of change and the importance of different drivers of change is critical to tidal marsh sustainability.

The overarching goal of this research is to examine how changes in natural and anthropogenic factors interact to affect tidal wetland distribution, extent and plant composition with the intent of promoting coastal resiliency to sea level rise impacts through informed coastal management. I quantified changes in marsh extent over the past 40 years and related changes in marsh extent to sea level rise and other drivers of change. Then I examined shifts in plant community composition throughout the Chesapeake Bay, VA, looking for signals of increased inundation and salinity. In small headwater systems, I explored the utility of these changes in plant composition for predicting soil sulfur content (an early signal of salinity intrusion). These changes in marshes from the past 40 years were used to elucidate results from an elevation-based model of future marsh persistence under accelerating sea level rise.

Several lessons emerged from this dissertation:

1. Analyses of changes in tidal marsh extent and plant communities are complementary, clarifying vulnerabilities and prognosis under future conditions.

2. Human shoreline use (e.g., development, shoreline hardening, boating activity) can dominate physical processes to alter the marsh response to sea level rise.

3. Defining sediment availability for a given marsh may not be sufficient to determine its potential for expansion or persistence under sea level rise.

5. Marsh plant communities can be an early signal of change, showing shifts in inundation frequency before there is any change in marsh extent.

6. Tidal marshes will continue to decline over the next 100 years. However, most of the loss will be in low salinity, riverine marshes. Some high salinity, Bayfront marshes will expand if the land they need to migrate is preserved.

7. Tidal marsh response to sea level rise has, and will continue to, vary by marsh form, geologic setting, location in the estuary, and surrounding land use decisions.

9. Targeted land use decisions coupled with active restoration may help minimize future marsh loss.