Semi-decadal transformations in geomorphology and landcover of a mixed-energy barrier island complex in North Carolina

Barrier islands, which cover the majority of the Atlantic coastline in North America, are highly valued and dynamic coastal landforms. Serving as natural protective barriers, these islands shield inland areas and critical infrastructure from storms and wave energy while providing vital habitats for diverse ecosystems that deliver key ecosystem services. With increases in storm frequency and sea level rise caused by climate change, these islands are becoming increasingly susceptible to change, making the understanding of their dynamics crucial for their preservation and the protection of the ecosystems and human communities they support. Research on barrier islands has predominantly focused on those facing the open ocean, with less attention given to the fetch-limited barrier islands (FLBIs) located in lagoons or sounds behind these ocean-facing islands. FLBIs are generally associated with minimal geomorphological changes under predominant conditions due to their sheltered nature. However, they can be highly susceptible to erosion during high-energy storm events, with slow morphological recovery due to the reduced movement of sediment by low wave energy in quiescent conditions. The Rachel Carson Reserve (RCR), located within the Inner Banks of North Carolina, is a complex of inlet FLBIs that contains diverse ecosystems and acts as a barrier to storm impacts for the town of Beaufort, NC. Bird Shoal, one of three islands in the RCR, is situated directly landward of Beaufort Inlet and serves as a frontline of defense from storms. Recent scientific focus on Bird Shoal revealed significant geomorphological developments that indicate the island’s departure from FLBI status and challenge the FLBI model. Specifically, Bird Shoal exhibited dynamic morphological changes outside of a storm event, while FLBIs are typically expected to exhibit minimal changes under predominant wave conditions. These observations coincided with significant widening of the Beaufort Inlet, which indicates a shift in the wave dynamics affecting the RCR. We conducted a mapping survey of the RCR using small unoccupied aircraft systems (sUAS) and compared the data with other remotely-sensed datasets to measure how the topography and shorelines of the Reserve changed from 2017 to 2023, with a specific focus on Bird Shoal. Our synoptic analysis demonstrated both erosion and accretion to Bird Shoal from 2018 to 2023. While Bird Shoal grew in area and volume, the majority of its shoreline experienced landward migration. The dynamic morphology of Bird Shoal may be caused by altered wave dynamics influenced by the widening of the Beaufort Inlet. Our study’s observed morphological changes to Bird Shoal and the potential wave dynamics at play suggest that the island deviates from the FLBI model. Additionally, the impacts of observed morphological changes were visible in a habitat change analysis, which indicated patterns of ecological succession within the RCR as a whole. For example, overwash from the migration of Bird Shoal appeared to provide a suitable platform for marsh growth. The observed morphological and habitat changes provide crucial insights into the future evolution of the RCR and inform strategic management approaches. Continued sea level rise will likely drive increased overwash and landward migration of Bird Shoal, reshaping the Reserve’s intertidal areas. The growth in dune width and elevation on Bird Shoal suggest increased sediment trapping capabilities, potentially strengthening the island’s role as a coastal barrier. However, the vulnerability of the dunes to overwash remains a concern. Implementing management strategies such as planting dune-stabilizing vegetation could mitigate this risk. Continued monitoring of both morphological and habitat changes is essential to understand the evolving dynamics of inlet barrier islands and support the effective management of the Rachel Carson Reserve.