Coastal Wetlands are at Greater Risk
Many coastal wetlands worldwide - including several on the U.S. Atlantic coast - may be more
sensitive than previously thought to climate change and sea-level rise projections for the 21st century.
U.S. Geological Survey scientists made this conclusion from an international research modeling effort
published December 1, 2010 in the journal Geophysical Research Letters, a publication of the American Geophysical Union.
Scientists identified conditions under which coastal wetlands could survive rising sea level.
Rapid / Slow Sea-Level Rise Scenarios
Using a rapid sea-level rise scenario, most coastal wetlands worldwide will disappear near the end of the 21st
century. In contrast, under the slow sea-level rise projection, wetlands with low sediment availability and low
tidal ranges are vulnerable and may drown. However, in the slow sea-level rise projection, wetlands with higher
sediment availability would be more likely to survive.
Valuable Marshes and Estuaries are at Risk
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 Glenn Guntenspergen, an author of this report. "This research is essential for allowing decision
makers to best manage local tradeoffs between economic and conservation concerns."
Previous Sea-Level Rise Assessments
"Previous assessments of coastal wetland responses to sea-level rise have been constrained because they did not
consider the ability of wetlands to naturally modify their physical environment for adaptation," said USGS scientist
Matt Kirwan, an author of this report. "Failure to incorporate the interactions of inundation, vegetation and
sedimentation in wetlands limits the usefulness of past assessments."
Sedimentation Rate and Tidal Range Interaction
USGS scientists specifically identified the sediment levels and tidal ranges (difference between high and low tide)
necessary for marshes to survive sea-level rise. 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, and the higher sediment concentrations in the water allow wetlands to build more elevation.
Importance of Coastal Wetlands
Coastal wetlands provide critical services such as absorbing energy from coastal 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.
Source of Sea-Level Rise Models
The rapid sea-level rise scenario used as the basis for this study is accredited to Stefan Rahmstorf at Potsdam
University, one of the contributing authors of the Intergovernmental Panel on Climate Change Fourth Assessment
Report. The slow sea-level rise projection is from the A1B scenario of the Intergovernmental Panel on Climate
Change Fourth Assessment Report.
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 | The marshes of Plum Island Estuary, Massachusetts are among those predicted by scientists to submerge during the next century under conservative projections of sea-level rise. Image credit: Matthey Kirwan, United States Geological Survey. |
 | Coastal marsh near Beluga, Alaska. Photo taken along Cook Inlet across from Anchorage Alaska. Image credit: James Lynch, United States Geological Survey. |
| Wetland on the eastern shore of Maryland at the Blackwater National Wildlife Refuge. Image by James Lynch, United States Geological Survey. |
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