Morphostratigraphic Differences Between Natural, Managed, and Constructed Coastal Foredunes

Coastal foredunes act as the first line of defense against oceanside flooding and buffer the most devastating impacts of hazards such as storm surge. Coastal communities are increasingly constructing artificial dunes and/or encouraging growth of semi-natural dunes for added protection. However, the impacts from storms on foredunes are highly spatially variable. This may be due, in part, to complex feedbacks between dune stratigraphy, sediment-vegetation interactions, and nearshore-beach-dune morphologynot all of which can be replicated in managed coastal systems. This study seeks to document internal morphostratigraphic differences between natural, managed, and constructed dunes to understand how the long-term sedimentological and ecological development of these features influences their resilience to storm impacts. Seven cross-shore transects of geophysical, sedimentologic, morphologic, and ecologic data were collected at sites representing a range of management histories (i.e., heavily constructed to natural) along the North Carolina Outer Banks, USA. Sixty-eight sediment cores, each up to 2 m in length, were collected from the dune toe to dune heel and analyzed for sediment texture, internal bedding, and biomass content. These data were paired with repeat, high-resolution, 3D topographic and ground-penetrating radar data to understand the controls on dune deposition and erosion. Preliminary results reveal more complex internal structure and higher variability within natural dunes as compared to constructed dunes in terms of 1) median grain size (-2.05 1.88 v. 0.282.01 ); 2) sorting (0.141.26 v. 0.180.91); 3) average belowground biomass (011.2% v. 00.56%); 4) apparent sedimentary structures (e.g., laminations, crossbeds); and 5) overall dune morphology (i.e., multiple established dune ridges and swales v. monomorphic form). These results indicate that the internal structure of dunes varies considerably between actively managed and naturally developed sections of coast. Further, the stratigraphic heterogeneity within the dunes underscores the relative contribution of both marine and aeolian processes in dune accretion. Ongoing work aims to understand how differences in internal structure affect the style and magnitude of dune erosion during major storm events.