New USGS-Led Study Could Help Pacific Wetlands Adapt to Sea Level Rise

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SAN FRANCISCO BAY, Calif. — A new study published Wednesday in Science Advances introduces an innovative tool to help resource managers preserve Pacific coastal wetlands from rising sea levels.

According to the article, even the lowest predicted rates of sea level rise could cause significant losses of Pacific tidal wetlands by the end of the century. Tidal wetlands provide many services for growing coastal communities. Their habitats filter water, sequester carbon, provide habitat for endangered species, protect communities from storm surges, and support local fisheries. To measure the vulnerability of these environments to sea level rise, researchers from the U.S. Geological Survey, University of California, Los Angeles, Oregon State University, Smithsonian Environmental Research Center and Queen’s University led a comprehensive study along the Pacific coast.

Photo of white egret in a southern California wetland.
Tidal wetlands provide habitat for species like the great white egret. (Credit: Kat Powelson, California Landscape Conservation Cooperative. Public domain.)

“This study is powerful because it brings together data from multiple experts to predict how different rates of sea level rise could affect tidal wetland habitats across the Pacific coast. It’s unique because it takes modeling results and translates them into possible scenarios for resource managers to evaluate and take action with,” says Dr. Karen Thorne, a USGS research ecologist and the paper’s lead author.

The project evaluated the vertical and horizontal response of 14 estuaries to a range of projected changes in rate of sea level rise. The scientists’ approach incorporated site-specific data on wetland elevation, tidal inundation, accretion rates, soil characteristics, and predicted rates of sea level rise into a dynamic process model to create high-resolution predictions of marsh vulnerability to sea level rise through the century. Study results indicate that the magnitude of marsh elevation lost varied by site and rate of sea level rise. However, the loss of tidal wetlands was highest in the latter part of the 21st century and under highest rates of sea level rise.

Under high rates of sea level rise (+142 cm for Washington and Oregon, and +166 cm for California), statistical models predicted that more than 86 percent of all wetland study sites, and 100 percent of tidal marshes in California and Oregon, could be fully submerged by 2110. Only two sites in the Pacific Northwest — Grays Harbor and Willapa National Wildlife Refuges — were projected to maintain higher relative elevations compared to the rest of the sites. Under a moderate sea level rise scenario (+63 cm in Washington and Oregon, +93 cm for California), 95 percent of high marsh and 60 percent of mid marsh were lost by the end of the century. Finally, under a low sea level rise scenario (+12 cm for Washington and Oregon, +44 cm for California), the scientists found that habitat composition remained similar over the coming century, except for in southern California, where high marsh habitats drowned in the latter part of the century.

The new modeling tool offers resource managers from the U.S. Department of Defense, Native American Tribes, National Wildlife Refuges, and coastal states with insight into a range of futures for Pacific tidal wetlands. Efforts to restore wetlands affected by human development may promote long-term marsh persistence and could mitigate the loss of important habitats in wetlands with higher initial elevations, high sediment supply or space to migrate upland. At sites where hard infrastructure and steep topography limit the upland migration of tidal wetlands, opportunities for nature-based adaptation solutions may be most effective early in the century, when rates of sea level rise are relatively slow. In the past, the U.S. Fish and Wildlife Service has used similar research led by Dr. Thorne to test techniques for helping southern California tidal marshes outlast sea level rise.

This study was led by the USGS Western Ecological Research Center. For more information about USGS research on sea level rise, visit the lead scientist’s project page.

More detailed results and figures are available in the full article “Coastal wetland resilience and vulnerability to sea-level rise,” which is available onlineProject funding came from the Department of Interior Southwest and Northwest Climate Science Centers, the USGS On The Landscape program, U.S. Fish & Wildlife Service, the USGS Climate and Land-Use Research and Development Program, and USGS Ecosystem Program.

WERC scientists heading out onto the Petaluma River
Tess Forstner (USGS) and Kevin Buffington (USGS) set out on the Petaluma River, CA. Under the guidance of Dr. Karen Thorne, they are studying the effects of rising seas on Pacific coastal wetlands. (Credit: Erika Sanchez-Chopitea/USGS. Public domain.)


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