Research ArticleECOLOGY

U.S. Pacific coastal wetland resilience and vulnerability to sea-level rise

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Science Advances  21 Feb 2018:
Vol. 4, no. 2, eaao3270
DOI: 10.1126/sciadv.aao3270
  • Fig. 1 We examined the vulnerability to SLR in 14 estuaries distributed along a climate, tidal, and latitudinal gradient.

    Sites varied in historic accretion rates, as determined from radio isotopic dating of sediment cores.

  • Fig. 2 WARMER projections of marsh elevation under three SLR scenarios.

    We incorporated low, moderate, and high SLR rates (6) into the WARMER model to project 2010–2110 change in mean marsh elevation. Under a low SLR scenario, many tidal marshes were projected to lose little elevation through most of the century. However, under higher rates of SLR, most wetland study sites lost mean elevation and did not “keep pace” with relative SLR, resulting in the loss of wetland elevation. MHHW is at z* = 1.0; mean tide level (MTL) is at z* = 0.0.

  • Fig. 3 Habitat projections from WARMER modeling under three SLR scenarios.

    Under moderate and high SLR scenarios, all study sites are projected to undergo substantial loss of elevation over the coming century, resulting in major changes in the composition of tidal wetland habitat types. By 2050, under moderate and high SLR scenarios, there is a gradual loss of high marsh habitats with an expansion of middle and low marsh habitats. Under moderate SLR scenarios by 2110, there is a loss of middle and high marsh habitats and submergence of tidal marsh, with a conversion to intertidal mudflat and open water at 36% of our study sites. Under high SLR scenarios, there is a total loss of all middle and high marsh habitats and submergence at 86% of the study sites, with three study sites going partly subtidal.

  • Fig. 4 Relative vulnerability of tidal marsh study sites to SLR.

    We assessed relative differences in overall wetland vulnerability across the Pacific coast by pairing available upland migration space with modeled vertical wetland elevation change under high SLR using WARMER. Migration potential index was calculated by dividing the current marsh area in the estuary by the area of suitable upland migration area. California sites were the most vulnerable because of substantial wetland elevation loss and minimal migration potential under a high SLR scenario. No study sites had enough low-elevation adjacent upland to allow 1:1 replacement of the current wetland area, and most wetlands had less than 50% available land for replacement. WARMER ratio was calculated by dividing the ending 2110 elevation by the beginning 2010 elevation under a high SLR scenario. WARMER ratio represents a site’s ability to maintain elevation through time. Colors represent risk at 25% intervals, from blue shades illustrating highest risks of submergence to green shades suggesting lowest risk of submergence from SLR.

  • Fig. 5 Modeling results illustrate changes from current habitat composition to greater extent of low marsh and mudflats under high rates of SLR at Newport Bay, which sits within the urban landscape of Southern California.

    (A) Currently, there is a mix of high, middle, and low marsh that provides habitat to a variety of endemic threatened and endangered wetland species, but (B) middle and high marsh habitats are projected to be lost by 2050, decreasing plant community complexity and diversity and available habitat. (C) Increased availability of waterbird habitat may occur with expansion of subtidal and intertidal mudflats, but the complete loss of wetland vegetation is projected to occur by 2110.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/2/eaao3270/DC1

    fig. S1. Available transgression or migration space under high SLR scenarios for the study sites.

    fig. S2. Projections of future sea level used in the WARMER modeling for high, moderate, and low SLR scenarios, from the National Research Council (6).

    fig. S3. 137Cs activity (in becquerel per kilogram) shown by depth with mean ± SE for sediment cores taken from sites in Southern California.

    table S1. Core elevation (in centimeters; relative to MSL) and accretion rate (in millimeters per year) for soil cores used in WARMER modeling.

    table S2. Sample size, mean elevation, and elevation range of real-time kinematic GPS (in meters; NAVD88) points collected at all study sites.

    table S3. Equilibrium elevations from WARMER.

    table S4. Elevation range of low, middle, and high marsh zones at each site.

    table S5. List of sediment cores taken from California, with locations, elevations, and estimated sediment accretion rate from 137Cs dating.

    table S6. WARMER model parameters for Pacific Northwest study sites.

    table S7. WARMER parameters for California study sites.

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. Available transgression or migration space under high SLR scenarios for the study sites.
    • fig. S2. Projections of future sea level used in the WARMER modeling for high, moderate, and low SLR scenarios, from the National Research Council (6).
    • fig. S3. 137Cs activity (in becquerel per kilogram) shown by depth with mean ± SE for sediment cores taken from sites in Southern California.
    • table S1. Core elevation (in centimeters; relative to MSL) and accretion rate (in millimeters per year) for soil cores used in WARMER modeling.
    • table S2. Sample size, mean elevation, and elevation range of real-time kinematic GPS (in meters; NAVD88) points collected at all study sites.
    • table S3. Equilibrium elevations from WARMER.
    • table S4. Elevation range of low, middle, and high marsh zones at each site.
    • table S5. List of sediment cores taken from California, with locations, elevations, and estimated sediment accretion rate from 137Cs dating.
    • table S6. WARMER model parameters for Pacific Northwest study sites.
    • table S7. WARMER parameters for California study sites.

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