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USGS Study: Rising Seas Put Pacific Coastal Wetlands At Risk Of Extinction, Some By 2050
Posted on Friday, March 02, 2018 (PST)

Individual species of animals, like polar bears, aren’t all that are at risk from climate change and the resulting accelerating rates in the rise in sea level. Pacific coastal wetlands are also at risk of extinction and the doomsday clock for Pacific Coast salt marshes isn’t that far off, according to a recent study by the University of California, Los Angeles, and the U.S. Geological Survey.


The study predicts that most of the tidal wetlands and salt marsh habitat along the Pacific Coast from Mexico to British Columbia will simply disappear by 2110, gobbled up by rising seas on one side and human development on the other, and some will disappear as soon as 2050.


The study looked at 14 estuaries along the Pacific Coast, using three scenarios – low, medium and high sea level rises – to measure tidal wetlands’ response to rising seas due to climate change. Under the low scenario, loss is minimal. With the high scenario, loss of coastal wetlands is almost total, particularly in California and Oregon.


“Throughout the U.S. Pacific region, we found that tidal wetlands are highly vulnerable to end-of-century submergence, with resulting extensive loss of habitat,” the study says. “Using higher-range SLR scenarios (rate of sea level rise), all high and middle marsh habitats were lost, with 83 percent of current tidal wetlands transitioning to unvegetated habitats by 2110.”


Estimates of the accelerating rates of sea-level rise along the Pacific coast range from 0.15 to 1.5 meters (0.5 to 4.9 feet) over the next 100 years and that, the study says, threatens the long-term sustainability of valuable tidal ecosystems.


Coastal ecosystems, including tidal wetlands, protect human communities from storm surges and rising sea levels, helping to ameliorate approximately $23.2 billion a year in damages along the U.S. Atlantic and Southern coastlines alone, the study says. They also provide other critical ecosystem services, such as endangered species and fisheries habitat, carbon sequestration, water filtration, and sediment trapping.


It went on to say that the wetland area lost was greater in California and Oregon – all of it would be lost – but still severe in Washington, with 68 percent submerged by the end of the century.


Some of the hardest hit by inundation of rising sea levels were found in Washington and Oregon at Grays Harbor, Willapa Bay and the Siletz River estuaries, but they also had some of the greatest opportunity for the wetlands to migrate inland. An assessment of rising sea levels on the Columbia River estuary was not included in the study.


Tidal wetland loss was also likely under more conservative scenarios, the study says, including the loss of 95 percent of high marsh and 60 percent of middle marsh habitats by the end of the century.


The researchers also concluded that much of the wetlands would not be able to just move inland as sea water inundates coastal areas.


“Horizontal migration of most wetlands was constrained by coastal development or steep topography, with just two wetland sites having sufficient upland space for migration and the possibility for nearly 1:1 replacement, making SLR threats particularly high in this region and generally undocumented. With low vertical accretion rates and little upland migration space, Pacific coast tidal wetlands are at imminent risk of submergence with projected rates of rapid SLR.”


“The bottom line is, especially in California (and he could add Oregon, according to the study), most of the salt marsh is going to go away by 2100,” said Richard Ambrose, a UCLA professor of environmental health and co-author of the paper. “Some will go away by 2050.”


Glen MacDonald, a UCLA distinguished professor of geography and another co-author of the paper, said loss of the wetlands would affect other ecosystems as well.


“We could see an ecological cascading effect” that affects breeding and food systems for fish, birds and other organisms, MacDonald said. “If you erase an entire system, the effects are going to ripple upward to predators and downward to prey species. It is just startling.”


Coastal marshes are able to adapt to sea level rise by shifting inland through a process called transgression, but the rocky, cliffy Pacific coastline as well as human development prevent that from happening in most places, MacDonald said.


“Especially in SoCal, we’ve developed up to the edge of almost every marsh,” Ambrose said. “That limits what the marshes can do and how they can respond. It makes them much more vulnerable.”


Coastal marshes are important to people too. Located at the bases of rivers and streams, the marshes process water and materials coming from farther inland, helping to remove pathogens. The marshes also offer unique cultural, recreational and educational opportunities.


“These are places where people can fish, canoe, kayak and hike around the coast,” said Karen Thorne, lead author of the paper and a researcher with the U.S. Geological Survey. “Wetlands are also great flood protection. After the stormy El Niño last winter, they acted like sponges to absorb that water.”


The paper’s results will help to inform policy decisions about what must be done — and how soon — to conserve the wetlands, Thorne said. One strategy involves acquiring upland property to allow the wetlands to adapt naturally. In places where cities butt up against the wetlands’ edges, however, that’s not an option, she said.


Other alternatives, such as adding sediment to raise the land, are more expensive. That option is currently being tested by Thorne and UCLA researchers at Orange County’s Seal Beach, where sea level rise is simulated because the ground has experienced subsidence, or sinking. Sediment was added one year ago, and for the next three years, researchers will monitor the area to see how well vegetation takes hold and to check other vital signs.


The study “U.S. Pacific coastal wetland resilience and vulnerability to sea-level rise,” was published online Feb. 21, 2018, in the Journal Science Advances (


Authors are Thorne; McDonald; Glen Guntenspergen, USGS; Richard Ambrose, Department of Environmental Health Sciences, UCLA; Kevin Buffington, USGS and Department of Fisheries and Wildlife, Oregon State University; Bruce Dugger, OSU; Chase Freeman, USGS; Christopher Janousek, USGS and OSU; and Lauren Brown, UCLA.


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