Barrier island bistability induced by biophysical interactions

Abstract

Barrier islands represent about 10% of the world's coastline 1 , sustain rich ecosystems, host valuable infrastructure and protect mainland coasts from storms. Future climate-change-induced increases in the intensity and frequency of major hurricanes 2 and accelerations in sea level rise 3,4 will have a significant impact on barrier islands 5,6 -leading to increased coastal hazards and flooding-yet our understanding of island response to external drivers remains limited 1,7-8 . Here, we find that island response is intrinsically bistable and controlled by previously unrecognized dynamics: the competing, and quantifiable, effects of storm erosion, sea level rise, and the aeolian and biological processes that enable and drive dune recovery. When the biophysical processes driving dune recovery dominate, islands tend to be high in elevation and vulnerability to storms is minimized. Alternatively, when the effects of storm erosion dominate, islands may become trapped in a perpetual state of low elevation and maximum vulnerability to storms, even under mild storm conditions. When sea level rise dominates, islands become unstable and face possible disintegration. This quantification of barrier island dynamics is supported by data from the Virginia Barrier Islands, U.S. and provides a broader context for considering island response to climate change and the likelihood of potentially abrupt transitions in island state.Barrier islands respond to rising sea level by migrating landward or drowning 7,9-10 . Landward migration is driven mostly by storms and is controlled by island elevation. Extensive measurements of dune elevation performed at the Virginia Barrier Islands 11 , a relatively undisturbed barrier system including 12 islands, show a bimodal distribution of barrier island elevation with two well-defined island types: low-elevation and highelevation islands (Fig. 1, Supplementary Fig. 1). Low islands lacking vegetated dunes are relatively narrow and prone to frequent overwash, resulting in rapid landward migration (Fig. 1a,b,g) and low biodiversity (as in the case of the islands associated with the Mississippi Delta, e.g., The Chandeleur Islands). In contrast, high islands with well-developed dunes resist storm impacts, are wider and migrate slowly (if at all, Fig. 1c,d,g) and support a rich ecosystem and/or human development. In this way, barrier island evolution is fundamentally linked to dune dynamics. However, because vegetated dunes both protect islands from storm impacts and are themselves

Sediment budget controls on foredune height: Comparing simulation model results with field data

“…We note that H max has been incorporated in two other papers that simulate foredune height and apparent stability regimes on barrier islands (Durán Vinent and Moore, ; Goldstein and Moore, ) and, thus, the results of those modelling efforts should be re‐appraised.…”

Lateral vegetation growth rates exert control on coastal foredune hummockiness and coalescing time

“…In the case of R > T c , environmental conditions may be conducive to bistable dynamics in the alongshore directionsimilar to the cross-shore models of Durán Vinent and Moore (2015) and Goldstein and Moore (2016) -with alternating stretches of dunes near the maximum height and lower intervening areas. In addition to storms, other factors such as a high water table, low sediment supply, grain size variability, development of shell lag and climatic conditions may also result in the suppression of the coalescing of coastal foredunes Russell, 2006, 2009;Wolner et al, 2013;Hoonhout and de Vries, 2016;Ruz and Hesp, 2014;Ruz et al, 2017a).…”

Interaction of seed dispersal and environmental filtering affects woody encroachment patterns in coastal grassland

“…). Biogeomorphic interactions between topography and vegetation are important drivers in barrier islands (Duran Vinent and Moore , Goldstein et al. , Zinnert et al.…”