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As sea levels rise, coastal wetlands are expected to change dramatically

Ghost forest in Nags Head Woods. Trees at the edge of the coastal forest have died as salt water seeps into their habitat.
NC Wetlands/Flickr
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“Ghost forest” in Nags Head Woods, North Carolina, where saltwater intrusion puts low-lying freshwater ecosystems at risk.

As sea levels rise, the ecosystems nearest to the water are most at risk.

In a new study led by the Wetland and Aquatic Research Center in Louisiana, scientists predict that sea level rise will result in dramatic changes to coastal wetlands. North Carolina is likely to be one of the most affected states in the U.S.

Coastal wetlands are both ecologically valuable and very vulnerable to sea level rise. They harbor a broad diversity of plant and animal species, including 70% of the rare or endangered species in North Carolina. Wetlands protect coastlines from storm surges and filter out pollution before it reaches open water. But rising sea levels threaten to “drown” saltwater wetlands in too-deep water, or seep inland and kill freshwater wetlands that can’t survive salt exposure.

Many researchers have tried to model how rising oceans will impact saltwater wetlands, but the new study is the first to predict the consequences to other nearby ecosystems. The researchers find that salt marshes and other saltwater wetlands will expand inland as sea level rises, which could increase the overall range of saltwater wetlands even as seaward salt marshes are lost to open water.

The problem is that the ecosystems they move into are most often freshwater wetlands. And geographic barriers, including both natural and human-altered terrain, will prevent freshwater wetlands from migrating in turn. The authors predict that large areas of freshwater wetlands will be overtaken by seawater, causing an overall loss of wetlands across the country.

Wetland adaptation may reduce the coming changes

Ken Krauss, a research ecologist at the Wetland and Aquatic Research center who is unaffiliated with the study, adds the caveat that wetlands can adapt to slow changes in water level.

“Wetlands don’t just sit there and take it,” he explains. “They have the capacity to build vertically and keep up with sea level rise.”

Small increases in water level cause aquatic plants to grow taller and trap more sediment, which in turn raises the elevation of the wetland. Accelerating sea level rise within the next fifty years could outpace wetlands’ maximum vertical growth, but their ability to adapt might make the fate of coastal wetlands less dire than the new study predicts.

Still, North Carolina’s four million acres of wetlands will likely be hit hard. The majority of state wetlands are freshwater wetland forests in the low-lying coastal plains, an area which is acutely vulnerable to sea level rise. The authors predict that about a quarter of the state’s freshwater wetlands could be transformed into salt marshes. This will threaten the diverse animal life that depends on freshwater wetland habitat — from migratory waterbirds to critically endangered red wolves. Saltwater intrusion is already killing swathes of coastal trees, leaving “ghost forests” of bare white trunks.

“North Carolina as a state has a lot to lose,” says Michael Osland, the lead author of the new study. “The important part is recognizing that these changes are coming and to anticipate and prepare for them.”

Ecologists may face a tradeoff between trying to preserve freshwater wetlands and helping saltwater wetlands survive by moving inland. Understanding how wetlands are likely to shift and change will help inform that decision.

Sophia Friesen is a science writer and WUNC’s 2022 AAAS Mass Media Fellow. Before working with WUNC, they wrote for science news outlets including Massive Science, preLights, and the Berkeley Science Review, covering everything from wildfire mitigation to pterosaur flight abilities.
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