Abstract
Barrier islands and their backbarrier saltmarshes have a reciprocal relationship: aeolian and storm processes transport sediment from the beaches and dunes to create and build marshes along the landward fringe of the island. In turn, these marshes exert a stabilizing influence on the barrier by widening the barrier system and forming a platform onto which the island migrates, consequently slowing landward barrier migration and inhibiting storm breaching. Here, we present a novel framework for applying these natural interdependencies to managing coastal systems and enhancing barrier-island resilience. Further, we detail application of these principles through a case study of the design of a marsh creation project that showcases the interdisciplinary engagement of scientists, engineers, stakeholders, and policymakers. Specifically, we describe: (1) the ecologic, sedimentologic, stratigraphic, and morphologic data obtained from the southern 4 km of Cedar Island (Virginia, United States) and nearby backbarrier tidal channels, tidal flats, and flood-tidal deltas, and (2) the use of those data to develop an engineering and design plan for the construction of a high (46 ha) and low (42 ha) fringing marsh platform located behind the island, proximal to a former ephemeral inlet. Additionally, we chronicle the process used to narrow five initial alternative designs to the optimal final plan. This process involved balancing best-available existing science and models, considering design and financial constraints, identifying stakeholder preferences, and maximizing restoration benefits of habitat provision and shoreline protection. Construction of this marsh would: (1) provide additional habitat and ecosystem benefits, (2) slow the rapid migration (up to 15 m/yr at present) of the barrier island, and (3) hinder island breaching. Ultimately, this project – presently at the final design and permitting stage – may enhance the storm and sea-level rise resilience of the island, backbarrier marshes and lagoons, and the mainland town community; and provide an example of a novel science-based approach to coastal resilience that could be applied to other global barrier settings.
Highlights
Coastal saltmarshes are long recognized for their ability to denitrify coastal waters; serve as habitat for birds, fish, and invertebrates; store coastal blue carbon; attenuate storm wave energy; reduce coastal erosion; and shelter mainlands from flooding (e.g., Howes et al, 1996; Pennings and Bertness, 2001; Shepard et al, 2011; Fagherazzi, 2014; Leonardi et al, 2018; Najjar et al, 2018)
likely to accelerate with sea-level rise
This approach can provide a temporary buffer for mainland communities
Summary
Coastal saltmarshes are long recognized for their ability to denitrify coastal waters; serve as habitat for birds, fish, and invertebrates; store coastal blue carbon; attenuate storm wave energy; reduce coastal erosion; and shelter mainlands from flooding (e.g., Howes et al, 1996; Pennings and Bertness, 2001; Shepard et al, 2011; Fagherazzi, 2014; Leonardi et al, 2018; Najjar et al, 2018) Backbarrier marshes, those situated directly landward of barrier islands, provide an additional and largely underrecognized function: they help to naturally stabilize fronting islands. Storms may be responsible for contributing inorganic sediment to saltmarshes in thicknesses up to several times that of normal annual accumulation (Rejmanek et al, 1988; Cahoon et al, 1995; Tweel and Turner, 2014) This sediment can enhance marsh growth by providing a fresh supply of nutrients and new sediment for root occupation (Baustian and Mendelssohn, 2015). These conditions allow a fringing marsh landward of the island to better maintain its tidal elevation and, enhance resilience of the barrier-adjacent marsh to sea-level rise (Nyman et al, 1995)
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