Barrier island migration dominates ecogeomorphic feedbacks and drives salt marsh loss along the Virginia Atlantic Coast, USA

Abstract

Abstract Coupling between barrier islands and their associated backbarrier environments (salt marsh, tidal flats) leads to complex ecogeomorphic feedbacks that are proposed to control the response of barrier island systems to relative sea-level rise. This study tests the applicability of these still-theoretical concepts through investigation of the Virginia barrier islands (eastern United States), which are located in an area of accelerated sea-level rise. Using historical maps and photographs from A.D. 1851 to 2010, we determine that rapid landward island migration (1–6 m yr–1) is leading to backbarrier area reduction and large-scale salt marsh loss (63 km2 or 19%) at a rate of 0.45 km2 yr–1. Landward barrier island migration far outpaces upland marsh migration and is responsible for 51% of marsh loss; the remainder is due to backbarrier processes (e.g., edge erosion). In direct contrast to proposed ecogeomorphic feedbacks linking barrier island and backbarrier environments, shoreline retreat rates were not related to changes in backbarrier marsh, open-water areas, or tidal prism. Rather, these results indicate that, for barrier island systems already undergoing migration, the primary barrier-backbarrier coupling is the loss of marsh and tidal-flat area because of barrier island migration.