Under projected rates of sea level rise, a bleak future for Pacific coast tidal wetlands

Under Projected Rates of Sea Level Rise, A Bleak Future for Pacific Coast Tidal Wetlands Pacific coast marshes, particularly those in California and Oregon, are highly vulnerable to climate change, according to a new modeling analysis. Under higher-range sea level rise scenarios estimated to impact this region by the end of the century, all high- and mid-marsh habitats are projected to be lost. Only the low marsh habitat is likely to survive under such conditions, the analysis indicates, and only at a few locations. The results begin to fill a notable gap in scientists' understanding of the way in which Pacific Coast marshes, in particular, will respond to rising sea levels, and may help to inform decisions about wetland restoration more broadly. To date, many scientists have suggested that the vulnerability of Pacific coast and other marshes has been overstated, though this debate is largely based on generalized observations. Here, using a novel, "scenario-based" approach to provide more granular insights, Karen Thorne and colleagues modeled the responses of tidal wetlands in 14 estuaries along the Pacific coast to projected changes in rates of sea-level rise (SLR). Critically, Thorne and her team collected and entered into their model site-specific data that captures how tidal wetlands "elevate" relative to sea level, through sediment buildup and production of organic matter - processes that vary from wetland to wetland. Devastating loss of coastal wetlands occurs under both high and intermediate estimates of SLR, the authors report. Most affected are California and Oregon, where 100% of most marsh habitat is lost. Even under more conservative SLR scenarios, the authors say, tidal wetland loss is notable, with 60% of mid-marsh habitats and 95% of high marsh habitats gone by the century's end. The results emphasize the high vulnerability of tidal wetlands in this region to sea-level rise.

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