The world's coastal wetlands may be more vulnerable to rising seas than scientists had suspected, a new study suggests.

The research, published yesterday in the journal Geophysical Research Letters, examined how sea level rise driven by climate change will affect wetlands during this century.

"The results suggest that most coastal wetlands in the United States will disappear under a rapid rate of sea level rise," said Glenn Guntenspergen, a landscape ecologist with the U.S. Geological Survey and an author of the new study. "Even under slower rates of sea level rise, there are a number of wetlands in the U.S. that are at risk because they have fairly low sediment supplies."

They include the nation's second-largest estuary, North Carolina's Albemarle-Pamlico Sound, and New England's largest estuary, Massachusetts' Plum Island Estuary.

"Coastal wetlands, to survive, have to respond," Guntenspergen said. "If sea level is rising, they have to increase their elevation."

Sediment deposition and decaying plant matter can help raise a wetland's elevation, he said. But if sea level rises too quickly, it can outpace the processes by which a wetland's elevation rises.

Seas rising faster than some models predict
"We actually suggest that if you get beyond sea level rise rates of 20 millimeters per year" -- roughly three-quarters of an inch -- "only a very few wetlands will survive," Guntenspergen said. "It will only be those that have very high suspended sediment concentrations in the water and have fairly high tidal ranges."

A wetland's tidal range is the difference in elevation between its high and low tide. A higher tidal range generally means more sediment reaches the marsh surface, Guntenspergen said.

In the new study, researchers examined two different scenarios for sea level rise this century. The low estimate came from the Intergovernmental Panel on Climate Change's 2007 report, which gave an estimate of sea level rise that did not include likely contributions from melting ice sheets in Greenland and Antarctica.

The high estimate is based on work by Stefan Rahmstorf of the Potsdam Institute for Climate Research, who has argued that climate models underestimate sea level rise. His estimates are based on a relationship between sea level rise and surface air temperature he derived from recent climate observations.

Guntenspergen said the new results could help scientists and policymakers develop strategies to increase wetlands' ability to adapt to rising sea levels. But he cautioned that his results are only "predictions of a possible response of wetlands, and we're continuing to do further studies to assess the accuracy of our modeling."

He and his colleagues are planning to test and further develop their model by examining data on sediment concentrations and elevation changes in a larger number of wetlands around the world.

Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC., 202-628-6500