EP052-0028
Investigating the Relative Roles of Sand Supply and Dune Vegetation on Foredune Morphology in the US North Carolina Outer Banks
Tuesday, 15 December 2020
Poster
Katya Jay1, Paige A Hovenga2, Laura J. Moore3, Peter Ruggiero4 and Sally Hacker1, (1)Oregon State University, Department of Integrative Biology, Corvallis, OR, United States, (2)Oregon State University, School of Civil and Construction Engineering, Corvallis, OR, United States, (3)University of North Carolina at Chapel Hill, Geological Sciences, Chapel Hill, NC, United States, (4)Oregon State University, Corvallis, OR, United States
Abstract:
Coastal foredunes defend against erosion and overtopping and provide other critical ecosystem services. Foredunes form via ecomorphodynamic feedbacks between sediment and burial-tolerant vegetation. Previous work has focused on the role of sand supply and beach geomorphology in shaping dunes, but less is known about the contribution of vegetation. Here, we quantify the relative roles of sand supply, beach geomorphology, and vegetation density to foredune morphology along the US North Carolina Outer Banks. We conducted surveys of beach-dune morphology and vegetation along the barrier islands and over multiple years, calculating beach and dune morphometrics, shoreline change rates (SCR; multidecadal from 1997-2016, interannual from 2016-2017), and dune grass parameters. Regression and hierarchical partitioning analyses were used to determine which variables were correlated with foredune shape metrics over the study period.
Regression models provided strong evidence that sand supply and beach morphology are most influential in controlling foredune height, while sand supply and dune grass density largely control foredune width. Foredune height was positively correlated with multidecadal SCR and negatively correlated with beach width, backshore slope, and increases in dune grasses, particularly the beachgrass Ammophila breviligulata. In contrast, foredune width was positively correlated with multidecadal SCR, foreshore slope, and beach width and negatively correlated with increases in A. breviligulata density. Changes in foredune height and width were positively correlated with interannual SCR and increases in A. breviligulata density, suggesting a positive feedback between sand supply and dune grasses. Our finding that increases in A. breviligulata density, in particular, explained the greatest proportion of variation in foredune width change aligns with previous findings in Pacific Northwest dunes.
