Many Coastal Wetlands Could Disappear This Century

Coastal wetlands around the world, including many on the U.S. Atlantic coast, could be more endangered by climate change and sea-level rise than previously thought, a new study suggests.

Coastal wetlands provide critical services such as absorbing energy from hurricanes and storms, preserving shorelines, protecting human populations and infrastructure, supporting commercial seafood harvests, absorbing pollutants and serving as critical habitat for migratory bird populations. These resources and services will be threatened as sea-level rise inundates wetlands.

The fates of coastal wetlands in the coming decades were studied by the U.S. Geological Survey using computer models that looked at projections of the potential rise of ocean water levels and warming due to the build up of greenhouse gases in the atmosphere. These models estimated how wetlands would respond under different rates of sea level rise and identified conditions under which coastal wetlands could survive rising sea level.

If sea level rises rapidly, most coastal wetlands worldwide will disappear near the end of the 21st century, the models found. But if sea level rises slowly, some wetlands could survive, depending on a few factors.

If a wetland has less sediment available to it and lower tidal ranges (the difference between high and low tides ), it would be more vulnerable and would likely drown. But if it has more sediment available to it and higher tidal ranges, it could survive.

This is because as water floods a wetland and flows through its vegetation, sediment is carried from upstream and deposited on the wetland's surface, allowing it to gain elevation. High tidal ranges allow for better sediment delivery.

Several coastal marshes along the east coast of the United States, for example, have limited sediment supplies and are likely to disappear this century. Vulnerable east coast marshes include the Plum Island Estuary (the largest estuary in New England) and coastal wetlands in North Carolina’s Albemarle-Pamlico Sound (the second-largest estuary in the United States).

"Accurate information about the adaptability of coastal wetlands to accelerations in sea-level rise, such as that reported in this study, helps narrow the uncertainties associated with their disappearance," said USGS scientist and study author Glenn Guntenspergen.

The study was published today (12/1) in the journal Geophysical Research Letters.

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