Salt marshes on the East Coast have accumulated soil more quickly over the past century-and some appear to be keeping pace with rising waters.

The world's salty, tidal marshes are hotspots of carbon storage and productivity, building up sediments and plant material so they can stay above sea level. Scientists wondering whether it's possible for wetlands to keep up with rising sea levels have revealed research that shows how salt marshes along the U.S. coast have responded-by building up elevation more quickly over the last century.

Two main factors affect how quickly a salt marsh accumulates soil: how much sediment is deposited in the wetland during tidal floods, and how much organic matter from the marsh's plants escapes decomposition. Humans can either choke sediment supply to marshes by building dams or increase the supply by causing erosion upstream, often through clearing land for agriculture. Cooler temperatures let more organic matter build up.

If sea level is rising slowly, sediment is plentiful, and vegetation is booming, a coastal wetland can keep pace with rising waters. But if sea level rises too quickly, that balance is lost.

"These feedback cycles allow a marsh to keep up and increase its rate of soil accretion up until a point where it just can't," said Nathaniel Weston, an ecosystems ecologist at Villanova University who led the study published in Earth's Future. "After that, it falls off the other end and can no longer exist as a marsh."

The new study is the first to assess the race on a large scale, comparing soil accretion rates using soil core from nine salt marshes from Maine to Georgia.

The dark, peaty columns record over 100 years of the marshes' histories, and researchers dated the soil to calculate how quickly the wetlands grew over time and how that rate changed.

Soil accretion sped up in all nine marshes-and six of them built soil at roughly the same rate as sea level rise over the past century. Three marshes in North Carolina, South Carolina and Virginia could not keep up with local sea level rise due to low sediment supplies from damming and warmer temperatures.

"This is the first study to document what's happening on this scale, across pretty much the entire East Coast," said Weston. "We were definitely excited to see fairly consistent results across our sites, where the marshes were increasing their rate of soil accretion."

Many coastal salt marshes around the world may be accelerating their growth, too, Weston said.

To slow the process of seawater inundation, communities could install "living shorelines" of vegetation to retain sediment, said Molly Keogh, a coastal geologist at the University of Oregon who was not involved in the study.

An expensive but temporary solution is to spray a slurry of mud and water over the marsh, which adds a few millimeters of sediment and can offset sea level rise a few years.

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