Healthy coastal wetlands would adapt to rising oceans

March 28, 2007

Tidal marshes, which nurture marine life and reduce storm damage along many coastlines, should be able to adjust to rising sea levels and avoid being inundated and lost, if their vegetation isn't damaged and their supplies of upstream sediment aren't reduced, a new Duke University study suggests.

Such marshes "offer great value as buffers of coastal storms in cities such as New Orleans, which is separated from the Gulf of Mexico by marshlands," Matthew Kirwan and A. Brad Murray said in a report published online on Monday, March 26, in the journal Proceedings of the National Academy of Sciences.

The researchers built a 3-D computer model that agrees with other recent work in suggesting that marshlands have some potential for adapting to environmental change. However, the Duke modeling also suggests that substantially disturbing the wetlands' plants or starving them of sediment could disrupt that equilibrium.

These coastal systems of water-tolerant plants and tidal channels also "provide highly productive habitat and serve as nursery grounds for a large number of commercially important fin and shellfish," according to the researchers. Murray is an associate professor of geomorphology and coastal processes at Duke's Nicholas School of the Environment and Earth Sciences. Kirwan, the report's first author, is a doctoral student working with Murray.

Despite those benefits, a variety of environmental changes often linked to humans -- including sea-level rise, sinking land and alterations to sand and silt supplies that anchor the wetland plants -- are "affecting coastal marshes worldwide," the scientists said.

The research was funded by the National Science Foundation and the Andrew W. Mellon Foundation.

The team's model, which was based partly on field studies done in South Carolina, and compared with observations in Louisiana, Massachusetts and British Columbia marshlands, uses computerized mathematical equations to help researchers evaluate the evolution of marsh shapes and complex ecosystems.

Other research teams have devised similar computer exercises, but Murray said Duke's version emphasizes how biology influences and interacts with physical erosion processes.

The model describes how vegetation and sediments can meld into living "platforms" that adjust to changing water levels. It also factors in how tidal creeks and channels can both supply silt and sand to the evolving matrix or help undo that process through erosion.

"With a steady, moderate rise in sea level, the model builds a marsh platform and channel network (that rises) with the rate of sea-level rise, meaning water depths and biological productivity remain temporarily constant," said the new report.

"If the vegetation is intact, it holds the system in place and enhances the trapping of sediments and tends to minimize the erosion," Murray said. "Up to some high level of sea-level rise, the system is going to keep itself in place because of that vegetation."

But the model also shows that removing some vegetation or reducing sediment supplies will set the stage for increasing water depths, a change exacerbated as the rates of rising sea levels increase.

Those changes might set the stage for "a scary metastable state," Murray said. Under that state, "conditions would tend to revert to an open-water subtidal basin that becomes too deep for the plants to come back," he said.

"We think that could be why marshes in the Chesapeake Bay region as well as in Louisiana are tending to deteriorate," he said. "That's because those are both places with relatively high sea-level rise rates, and because of land-use changes that decrease rates of sediment delivery downstream."

Such land-use changes could include the damming of rivers and the reforestation of formerly open land.

Source: Duke University

Explore further: Coastal property values could erode if nourishment subsidies end

Related Stories

World's shrinking groundwater 'needs better governance'

December 30, 2013

An eminent Australian water scientist has urged the world to take better care of its groundwater resources – or risk dangerous scarcities, economic impacts and potential conflicts in coming decades.

Rivers buckle under pressure from climate, dams

March 21, 2011

Climate change is likely to intensify the alarming rate of degradation of the world’s rivers and wetlands unless water resources are better managed, according to a special issue of the international scientific journal ...

Planning strategies needed to protect food sources

August 6, 2009

( -- Climate change and urban expansion could threaten the sustainability of horticultural industries in the Adelaide Hills unless a long-term strategy is employed, according to a senior geographer at the University ...

Recommended for you

Most EU nations seek to bar GM crops

October 4, 2015

Nineteen of the 28 EU member states have applied to keep genetically modified crops out of all or part of their territory, the bloc's executive arm said Sunday, the deadline for opting out of new European legislation on GM ...

The dark side of Nobel prizewinning research

October 4, 2015

Think of the Nobel prizes and you think of groundbreaking research bettering mankind, but the awards have also honoured some quite unhumanitarian inventions such as chemical weapons, DDT and lobotomies.

Internet giants race to faster mobile news apps

October 4, 2015

US tech giants are turning to the news in their competition for mobile users, developing new, faster ways to deliver content, but the benefits for struggling media outlets remain unclear.

Fusion reactors 'economically viable' say experts

October 2, 2015

Fusion reactors could become an economically viable means of generating electricity within a few decades, and policy makers should start planning to build them as a replacement for conventional nuclear power stations, according ...


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.