Salt Marsh SOS
From Maine to Mississippi, Tidal Wetlands are Degrading
A picture may speak a thousand words, but time-lapse photographs of an imperiled tidal marsh in Darien, Connecticut are more likely to leave viewers speechless.
In a scientist’s photomosaic taken in 1972, wetlands along the Five Mile River included a small island surrounded by thin ribbons of water and covered in grasses that typify a healthy New England salt marsh. In a contrasting set of photos from 2000, all that remains of the island is a puddle-pocked mudflat. The watercourses are wider, no longer so meandering, and the surrounding stands of Spartina patens and Spartina alterniflora are frayed.
"Some residents on the Five Mile River showed us photographs from the 1960s, and today, they [the marshes] are virtually all gone. They were very lush before," says Ron Rozsa, a coastal ecologist at the Connecticut Department of Environmental Protection.
The photographs depict a troubling phenomenon along the U.S. Atlantic and Gulf Coasts: Tidal wetlands that have been healthy for hundreds, if not thousands, of years are rapidly breaking up and converting to open water.
Some of the losses are well understood, like in Louisiana, where diversions and levees on the Mississippi River have stopped nourishing sediments from replenishing the delta. Twenty-four square miles of the state’s wetlands sink into the Gulf of Mississippi each year—the equivalent of one football field every 38 minutes.
Among the other widely known problem spots is the Jamaica Bay National Wildlife Refuge in New York, where salt marshes suffer from a perfect storm of sediment starvation, dredging, wastewater effluent and even wave action from boats that threatens to drown them by 2020. Maryland’s Blackwater National Wildlife Refuge faces similar peril, made worse by nonnative rodents that are eating away the bulrush marshes.
Research by a team of University of Maryland scientists suggests these notable losses may just be the beginning. By analyzing NASA satellite imagery of the East Coast, the team is categorizing the health of wetlands to detect areas that are at risk for rapid loss. Their technique is not without its pitfalls, since atmospheric conditions can cloud the images and the satellites don’t capture every detail. Still, the team’s data pinpoint dozens of locations from Massachusetts" North River Estuary to Hunting Island off the South Carolina coast where marshes are in trouble.
The team is paying particularly close attention to Chesapeake Bay, the nation’s largest estuary system. They found that in 1993, 50 percent of the bay’s marshes could be classified as degraded, with 20 percent seriously degraded. Michael Kearney, the team’s leader, expects to publish an update this year, and the news is not good. "Those areas that were visibly degraded have gotten much, much worse," he says.
The University of Maryland team’s findings, while more severe, echo what Rozsa’s Office of Long Island Sound Programs is observing in Connecticut. By comparing low-altitude aerial photographs of the sound’s coast and tidal rivers from 1974, 1995 and 2000, researchers have identified dozens of locations where marshes are shrinking, with areas near the middle of tidal rivers particularly hard hit. Rozsa estimates Connecticut’s tidal wetlands have shrunk by at least 30 percent since 1974, with some locations losing up to 90 percent.
Connecting the dots between wetlands that are far apart is a tricky business, given the extraordinary complexity of the ecosystems and the fact that each faces unique local factors. But there is one common denominator that scientists keep coming back to: sea-level rise.
The oceans have been rising since the end of the last Ice Age 10,000 years ago, and the rate of rise on the East Coast has been fairly steady since the 1850s. According to one prediction, sea-level rise alone will cause a 22 percent loss of the world’s wetlands by 2080.
Given the economic and biological importance of wetlands, the time to act is now, says Tundi Agardy, a consultant for the New Hampshire nonprofit Clean Air, Cool Planet. Agardy has been traveling to New England towns to brief officials on steps they can take to prepare for climate change. One piece of advice is to remove bulkheads to allow endangered wetlands to migrate; another is to rewrite zoning regulations to require that buildings be set back farther from the shoreline.
James Titus, the U.S. Environmental Protection Agency’s project manager for sea-level rise, says a long-term solution would be for governments and environmental organizations to buy "shore easements" from property owners. The easements would allow development as long as owners promise not to armor the shoreline, and ownership of lands that would be inundated by the rising sea would revert to the easement purchaser.
Titus estimates the cost of a nationwide program at between $373 million and $1.2 billion. "We have the opportunity to plan for the gradual landward migration of these ecosystems, but once that land is developed, the opportunity is lost," he says.