Effect of sea level rise on the coastal protective services of Pacific Northwest salt marshes

INTRODUCTION Coastal vegetated habitats are on a global decline due to climate change, specifically sea level rise (SLR) and increased storminess (IPCC, 2014). These fringing environments connecting land and sea are important mediators of SLR and increased wave action, providing essential ecosystem services such as coastal protection, water purification, and erosion control (Barbier et al., 2011). However, as coastal vegetation declines due to human activity and environmental change, vulnerability of these shorelines to erosion and flooding increases (Gedan et al., 2011). Salt marshes, in particular, are essential for coastal protection as they provide the ecosystem functions through which many negative impacts of SLR can be minimized. Salt marshes dissipate wave energy through tall vegetation, stabilize sediment through root systems, and can increase intertidal elevation and extent through accretion (Barbier et al., 2011). Accretion occurs when sediment-laden water is slowed by vegetation, releasing sediment that is then deposited on the marsh surface. This process results in a change in marsh surface elevation relative to SL, as well as an increase in marsh extent, and is influenced by incoming sediment load and vegetation type. How salt marshes ultimately respond to variable SL will likely depend on species-specific difference in accretion ability, sediment supply, and local effects of SLR (Pethick, 1981).