Field and modeling investigations into the drivers and implications of beach and saltmarsh shoreline erosion: Examining the impacts of geomorphic change on coastal carbon budgets and the role of sea-level anomalies in facilitating beach erosion.

Coastal landscapes, such as saltmarshes and barrier islands, evolve across timescales ranging from storm events to millennia in response to a number of physical and anthropogenic drivers. Proper management of these dynamic environments hinges upon a strong scientific understanding of the processes that shape the coast as well as the implications of coastal change. The first chapter of this dissertation presents measurements of beach erosion along a transgressive barrier island related to sea-level anomalies, which are short-term, non-storm fluctuations in water level. These phenomena are recognized along entire continental margins, but are not included in coastal management plans. Erosion measurements from a barrier island in North Carolina indicated that similar amounts of erosion were observed in a year with frequent sea-level anomalies as a year with a hurricane impact. This work suggests that anomalies can exacerbate the impacts of storms, long-term sea-level rise, and human impacts. The second chapter describes a carbon budget model that was developed for mainland fringing saltmarshes that includes shoreline erosion, which is a process largely ignored in marsh carbon assessments. The final chapter extends the marsh carbon budget to transgressive barrier islands and explores the impact of erosion, overwash, and geologic setting on barrier island carbon budgets and reservoirs. Saltmarshes are considered carbon sinks because of high carbon burial rates and a carbon reservoir that is presumed to increase through time; however, the global prevalence of marsh loss suggests that marsh carbon budgets must also include carbon export from erosion. Carbon budget box models for mainland fringing saltmarshes and transgressive barrier islands were developed that include both carbon storage across the marsh platform and carbon export from shoreline erosion. The fringing marsh model was applied at an eroding fringing marsh and the output indicates that erosion can switch a marsh from functioning as a sink to a source. The barrier island model was applied at two transgressive barriers and results suggest that erosion, overwash, and human impacts contribute to the transition of a barrier to a carbon source, which results in a reduction in the carbon reservoir through time.Doctor of Philosoph