Salt marshes in Barnstable, Massachusetts show signs of erosion and submergence as sea levels rise (December 2, 2022).Credit: Erin Peck
Creating wetlands, which are being submerged by rising sea levels, remains a challenge, but scientists are now one step closer to identifying a solution.
Amid climate change, large-scale dam removal projects are gaining traction as a solution to the loss of coastal wetlands that reduce flooding, filter water, and provide habitat for wildlife. However, in a recently published paper, scienceresearchers concluded that this strategy does not work in most rivers in the United States.
Limited sediment supply hinders wetland recovery
The reason is that there is not enough sediment. Of the nearly 5,000 rivers analyzed, nearly three out of four were unable to transport enough sediment to keep up with sea level rise in the coastal regions they connect to. Nearly half were at least 10 times short of the required amount of sediment.
This is the first national study to examine how much watershed sediment can be deposited in coastal areas by rivers. So far, research has focused on a few very large rivers. mississippi,and, Elfa In Washington, they are not representative of most other areas of the continental United States.
Most watersheds in the United States are small and are not major sources of sediment buildup in wetlands, researchers said. It is on these small rivers that most dams are located.
Expert insights on dam removal and sediment supply
The study was led by Dr. Scott Ensign, a research scientist at the Stroud Water Research Center, a nonprofit organization that studies freshwater streams and rivers around the world. He said: “Elfa is the poster child for dam removal projects that restore coastal sediment, and for good reason: it liberated vast amounts of sediment and sand.
“However, rivers along the East and Gulf coasts are not as steep as the West Coast and there is less sediment that can reach the wetlands, so the wetlands are wider and require more sediment to keep them above the rising ocean.” is required.Basically, the numbers don’t add up.”
Dr. Christopher Craft, an Indiana University professor who focuses on wetland restoration and climate change, said, “The extensive and comprehensive spatial analysis conducted by the authors shows that sediment supply in most coastal basins is This strongly suggests that this is insufficient.” As sea levels rise, tidal wetlands appear. In other words, sediment cannot save them. ”
Methodology and findings
Ensign and her co-authors, Joanne Halls of the University of North Carolina Wilmington and Erin Peck of the University of Massachusetts, used publicly available data from the U.S. Geological Survey and the National Oceanic and Atmospheric Administration to map watersheds to coastal wetlands. Sediment supply was modeled. Uses Esri’s ArcGIS Pro technology. They then compared their projections to previously reported rates of change for tidal wetlands across the United States.
“By and large, the sediment that saves most wetlands from drowning doesn’t come from upstream rivers. In many places on the East Coast, removing dams won’t help. You’ll have to look elsewhere.” explained the lieutenant.
Impact on wetland conservation
Dr. James Pizzuto, a professor of geological sciences who specializes in river science at the University of Delaware, said the researchers deftly addressed a complex problem. “These results, and the local variations documented by mapping the entire U.S. coastline, provide important guidance to managers and scientists, and future efforts to investigate other processes beyond basin sediments. “We are documenting where we should focus our efforts,” he said.
Such efforts include finding ways to retain more mineral deposits, plant material and organic carbon in wetland soils, said Donald F. Boesch, professor emeritus at the University of Maryland Center for Environmental Science. He explained that it was possible. “This is true both where sediment is being depleted and where it is being diverted to construct and maintain wetlands with relatively high rates of sea level rise, such as the Mississippi Delta,” he said. ” he said.
Future research and conservation strategies
Future research is needed to measure how much sediment is trapped behind a particular dam and accurately predict the impact on downstream tidal wetlands.
“In general, the most important action to protect tidal wetlands is to allow them to move up slopes. In some areas, we need to restore natural hydrology and protect lowlands,” said Ensign. Direct application of deposits and other engineering approaches may also be helpful at very local scales.”
References: Scott H. Ensign, Joanne N. Halls, and Erin K. Peck, “Catchment Sediments Cannot Offset Sea Level Rise in Most U.S. Tidal Wetlands,” December 7, 2023. science.
DOI: 10.1126/science.adj0513
The National Science Foundation funded the research.
Source: scitechdaily.com
