Differences in Internal Sedimentologic and Biotic Structure Between Natural, Managed, and Constructed Coastal Foredunes

Coastal communities are increasingly constructing artificial dunes and/or encouraging dune growth for added protection against storm surge. However, the morphological response of foredunes to storm impacts varies greatly, even over short spatial scales. This may in part reflect anthropogenic influences on dune ecomorphostratigraphy. While the role of beach and dune management is increasingly recognized for altering sediment supply to, and the shape of, foredunes, the management-dependent effects on the internal architecture of the dune are poorly constrained. Here, we document the internal architecture of natural, managed, and constructed foredunes using direct field topographic and subsurface measurements from seven sites along the North Carolina Outer Banks, USA to quantify differences in dune morphology, sedimentology, stratigraphy, and belowground ecology. We found significant differences in internal biotic and sedimentologic structure between dune types, with natural dunes having the most complex architecture. Natural dunes have the most variable sediment texture (median grain sizes: -2.05-2.18 Phi; sorting: 0.14-1.26 Phi), greatest degree of interbedding (>8 beds at least 1.5 cm thick per vertical meter), greatest abundance of apparent sedimentary structures (e.g., laminations, crossbeds), most complex depositional patterns, and highest living (128.5 g/m(2)) and non-living (183.9 g/m(2)) belowground biomass, root surface area (16,674.2 cm(2)/m(2)), and average organic matter content (0.68%). In contrast, managed and constructed dunes have less variable sediment texture (median grain sizes: -1.66-2.18 Phi [managed], -1.24-2.64 Phi [constructed]; sorting: 0.16-0.90 Phi [managed], 0.14-0.91 Phi [constructed]), lower degrees of interbedding, fewer apparent sedimentary structures, and weaker internal biotic structure. The differences in internal architecture between dune types reflect the divergent physical processes governing dune evolution for natural, managed, and constructed foredunes. The results provide new insight into the influence of management choices on internal dune structure, which has direct implications for the protective services of dunes during major storm events.