NEW INSIGHTS INTO BARRIER ISLAND EVOLUTION: DUNE-SHRUB ECOMORPHODYNAMICS, IMPACTS OF BARRIER MIGRATION ON CARBON BUDGETS, AND THE LONG-TERM EFFECTS OF ROADWAY MANAGEMENT

Barrier islands are highly dynamic coastal landforms which evolve over time in response to different natural and human-influenced processes. Because barrier islands protect mainland communities from storms and provide valuable ecosystem services, understanding and predicting how barriers will change in the future is important. In my dissertation, I investigate three aspects of barrier island dynamics including dune-shrub interactions, contributions to the carbon budget from island migration, and the effects of roadway management on barrier island evolution. In Chapter 1, I investigate the ecomorphodynamic relationship between shrub presence and barrier island geomorphology, using observational data and a machine-learning model to predict barrier island shrub presence in the Virginia Barrier Islands (VBI). Shrub growth and persistence is predicted by foredune elevations higher than 1.9-m and island widths greater than ~160-m maintained for >7 years, and both shrub expansion and removal tend to lag these thresholds. In Chapter 2, I estimate the amount of organic carbon (C) release associated with future barrier island migration for a system like the VBI using a coupled barrier island model (CASCADE) and representative stratigraphy. Estimates of C release depend on island retreat rates, with higher rates of sea level rise and more intense storms increasing C release estimates. Additionally, C release is modulated by the C content of the eroded stratigraphy, with the erosion of thicker carbonaceous bay and marsh stratigraphy increasing C release and the erosion of thinner carbonaceous units decreasing C release. In Chapter 3, I explore the effects of different roadway management strategies and climate change scenarios on decadal- and centurial-scale barrier island evolution, using a version of CASCADE calibrated to represent Ocracoke Island, North Carolina. Model results reveal that roadway management strategies which decrease washover deposition lead to narrower and lower island morphologies with a greater tendency to drown, highlighting how management strategies designed to maintain traditional transportation corridors can prevent island rollover and hasten island loss. Taken together, these chapters highlight the complexity of barrier island dynamics, demonstrating the importance of geomorphic thresholds, barrier island contributions to the C budget and the potentially counter-productive effects of current barrier island management strategies.