Study yields new clues to predict tipping points for marsh survival

February 13, 2019 by Tim Lucas, Duke University
A Duke University study of hundreds of US estuaries has yielded new clues to predict tipping points for marsh survival. Pictured here, Oak Island, N.C. Credit: Anna Braswell

Sea-level rise, sediment starvation and other environmental woes pose increasing threats to coastal wetlands worldwide. But a massive new Duke University study could help stem these losses by giving scientists a broader understanding of which wetlands are most at risk, and why.

The study, which assessed wetland distribution and resilience in hundreds of U.S. estuaries, found that it's all a matter of scale.

"At the local level, the persistence or loss of coastal marshes was invariably linked to feedbacks between two factors: erosion, which eats away at marsh edges, and vegetation, which stabilizes them," said Anna E. Braswell, a Ph.D. graduate of Duke's Nicholas School of the Environment, who conducted the research as part of her 2017 dissertation. "But at broader spatial scales, other key drivers emerged, too."

As the researchers took more of an 's surrounding geography into account, the depth, size, shape and latitude of the estuary became increasingly important predictors for determining the extent of wetlands it could support, Braswell said. The shape and orientation of the nearby coastline and the depth of near-shore waters mattered, too.

And the amount of replenishing sediment being carried into the estuary by rivers or incoming tides became a key indicator of marshes' resilience to change.

"These macro-scale coastal and watershed characteristics accentuated or limited the stabilizing impacts of the local feedbacks," she said. "But they weren't really evident until we took a few steps back and viewed the estuaries from broader spatial perspectives."

"What this tells us is that salt marshes everywhere probably have tipping points," said co-author James B. Heffernan, assistant professor of ecosystem ecology and ecohydrology at the Nicholas School.

Researcher Anna Braswell samples soil from an estuary during her dissertation research on 'tipping points' for wetland preservation. Credit: Megan Fork
"Knowing what causes these tipping points to vary from location to location is an important step in identifying where we should expect marshes to be especially vulnerable to future change," he said. "It also provides a framework for understanding where wetland restoration is likely or not likely to succeed."

Coastal provide a long list of ecosystem services that benefit humans, including shoreline protection, pollution filtration, flood prevention, fishery habitat and carbon sequestration.

Braswell and Heffernan published their peer-reviewed findings Jan. 31 in the journal Ecosystems.

Using existing , they analyzed hundreds of estuaries on the U.S. Atlantic and Gulf coasts from Maine to Mexico to determine the fraction of each estuary that was occupied by wetlands and identify the factors that controlled the extent of the wetlands' spread and their resilience to change.

Each site was analyzed at five different geographic scales—from macro-analyses that covered the entire estuary and its adjacent coastline and watersheds, to fine-scale analyses that zeroed in on what was happening in small, individual tributaries.

"Integrating data from five different scales allowed us to see patterns and linkages that we would have missed otherwise," said Braswell, who now works as a research scientist in the Earth Lab at the University of Colorado at Boulder. "This information will be vital for future preservation and restoration efforts."

Braswell and Heffernan used data from the National Wetlands Inventory and other publicly accessible sources to do their analyses. The five spatial scales they used—sub-region, basin, sub-basin, watershed and sub-watershed—correspond to standard U.S. Geological Survey hydrological units.

Explore further: Urbanization is cutting off life support to NYC's wetlands

More information: Anna E. Braswell et al, Coastal Wetland Distributions: Delineating Domains of Macroscale Drivers and Local Feedbacks, Ecosystems (2019). DOI: 10.1007/s10021-018-0332-3

Related Stories

Urbanization is cutting off life support to NYC's wetlands

September 24, 2018

Historically, salt marshes have not only served as ecological nurseries for fish, birds, and other wildlife—they've been stalwart defenses against coastal storms. But recently, coastal development coupled with accelerated ...

Recommended for you

Meteorite source in asteroid belt not a single debris field

February 17, 2019

A new study published online in Meteoritics and Planetary Science finds that our most common meteorites, those known as L chondrites, come from at least two different debris fields in the asteroid belt. The belt contains ...

Diagnosing 'art acne' in Georgia O'Keeffe's paintings

February 17, 2019

Even Georgia O'Keeffe noticed the pin-sized blisters bubbling on the surface of her paintings. For decades, conservationists and scholars assumed these tiny protrusions were grains of sand, kicked up from the New Mexico desert ...

Archaeologists discover Incan tomb in Peru

February 16, 2019

Peruvian archaeologists discovered an Incan tomb in the north of the country where an elite member of the pre-Columbian empire was buried, one of the investigators announced Friday.

Where is the universe hiding its missing mass?

February 15, 2019

Astronomers have spent decades looking for something that sounds like it would be hard to miss: about a third of the "normal" matter in the Universe. New results from NASA's Chandra X-ray Observatory may have helped them ...

What rising seas mean for local economies

February 15, 2019

Impacts from climate change are not always easy to see. But for many local businesses in coastal communities across the United States, the evidence is right outside their doors—or in their parking lots.

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.