UM study reveals continuing decline of bay wetlands

April 12, 2002|By Frank D. Roylance | Frank D. Roylance,SUN STAFF

Satellite data that can track the drowning of tidal wetlands by rising sea levels across the Chesapeake and Delaware bays have revealed trends that point to the virtual disappearance of the bays' marshes by the end of this century.

The University of Maryland study found that by 1993, about 70 percent of all the marshes around the Chesapeake and Delaware bay estuaries combined had become slightly to completely degraded. About 30 percent remained healthy, according to geologist Michael S. Kearney, lead author of the study.

The percentage of Delaware Bay marshlands degraded by rising sea levels more than doubled between 1984 and 1993, increasing from 25 percent to 54 percent of the total, the study found.

The process has continued since 1993. Kearney returned in the winter to sites he had visited a decade ago in Blackwater National Wildlife Refuge on Maryland's lower Eastern Shore.

"In 1993 when I was out there, it wasn't a great marsh in terms of its health," he said. "It's all gone now."

With sea levels predicted to rise during this century at rates two to three times those in the 20th century, Kearney said, few of today's remaining marshlands will survive through 2100.

The findings by Kearney and his group at College Park, and at the university system's Center for Environmental Science at Horn Point, are to be published next week in Eos, a publication of the American Geophysical Union.

The loss of tidal marshes would threaten the bays' fisheries, waterfowl and other wildlife, the study said. Water quality and clarity also would degrade as shorelines erode and the marshes' ability to filter runoff from the land declines.

As the marsh plants decay, the carbon once locked in that organic matter would be released to the ocean and atmosphere as carbon dioxide - a greenhouse gas, which most scientists believe contributes to global warming.

The phenomenon of declining marshlands raises important policy issues, but public officials have a hard time seeing how they can have an impact during their tenures.

"That makes it a very difficult issue to sell. It's not getting the kind of attention it needs in the long run," said Bill Street, director of watershed restoration at the Chesapeake Bay Foundation.

But in time, political leaders and landowners will have to confront questions about protecting the tidal wetlands that survive, and where to allow the marshes' inland migration as sea levels continue to rise.

"We're talking about people's property, and those owners may have a different point of view about letting marshes take over their property," said James G. Titus, project manager for sea-level rise at the U.S. Environmental Protection Agency.

Although scientists and bayside residents have been aware of rising sea levels and eroding marshes and islands for many years, actual measurement of the losses has been problematic.

Local measurements were accurate, but wide variations in such local factors as wave action and sedimentation rates around the bay made it difficult to gauge what was happening to the estuaries as a whole.

"People were generally aware that the Blackwater wildlife reserve was losing wetlands," said Titus. "But the idea that this was more general to the Chesapeake and Delaware bays hadn't been established."

Rising seas are threatening tidal wetlands throughout the world. Kearney and his group hope to expand their study to other U.S. coastal regions.

The five-year, $900,000 Maryland study, funded mostly by NASA, documents the marshes' retreat using data gathered between 1984 and 1993 by the space agency's Landsat satellites. The imagery allows scientists to distinguish among the light frequencies being reflected by marsh plants, bare mud and open water.

Using a computer model they developed, the team members have converted the data into maps that show, over time, where marsh plants are gradually dying, thinning and giving way first to mud, then to open water.

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