On the Atlantic Flyway, it takes more than a handful of gravel or an asphalt patch to fix a pothole. It takes a giant dredge pumping an arc of slurry at rock-concert decibels for hours at a time, day after day, with funding that would make many municipal road managers envious.

But these are no ordinary potholes, and the flyway is no road. It’s a major migration route for a host of songbirds, shorebirds and waterfowl. And one of its most important pit stops, Blackwater National Wildlife Refuge, is in jeopardy as water gobbles holes in the vast golden-brown marsh on which the birds rely, as do fish, crabs and other wildlife.

This $1.4 million “thin-layering” project, as the dredge-pumping has come to be called, is the first of its kind in the Chesapeake Bay. From late November until mid-December, the refuge and its partners transferred 26,000 cubic yards of sediment from the Blackwater River to 40 acres of marsh near a boat ramp called Shorters Wharf.

The sediment, taken from a meander that will replenish itself just a few hundred yards away, will elevate the marsh surface 4–6 inches — enough to keep the plants from drowning. Even just that thin layer, researchers believe, should reverse the current disintegration of the root zone, which suffers from excessive flooding.

Rising sea level, coupled with subsidence of the land, is causing drastic changes to the Blackwater landscape. A casual visitor can spot them: loblolly pines, once leafy and tall, are but mere sticks, denuded. The once-thick carpet of marsh is fragmented, with more lost all the time. If nothing is done, said refuge biologist Matt Whitbeck, the Chesapeake could lose one of its most productive ecosystems, not to mention one of its largest outdoor attractions.

“These marshes, they’re valuable in so many ways, and to so many different people. They are part of the cultural fabric of these communities,” Whitbeck said. “When these marshes go away, they don’t come back. That’s why these restoration projects are so important. They help us hang on.”

If it works as predicted, this thin layer will help the flooding low marsh revert to high marsh. Whereas the low marsh, mostly made up of the wetland grass, Spartina alterniflora, is inundated twice a day by the tidal cycle, the high marsh takes on water more rarely. High marsh supports a different grass, Spartina patens, and its golden, hay-like stalks are the preferred habitat of the saltmarsh sparrow and the black rail.

The saltmarsh sparrow population is declining 9 percent a year, with only 53,000 left in the Eastern United States. David Curson, director of bird conservation for Audubon Maryland-DC, said he is seeing fewer of the sparrows at Blackwater, probably because of the saltwater inundation.

The black rail, once common at Blackwater, has declined more than 85 percent since the early 1990s, according to a 2006 survey. Curson said he has never seen one, despite multiple bird surveys he’s conducted in the marshes in the past decade.

The project, which will cost a total of $3.5 million, is the largest wetlands restoration in the Blackwater refuge, which has been called Ground Zero for sea level rise in Maryland. Funds for the project came from various federal agencies, including the U.S. Fish and Wildlife Service and the U.S. Department of Agriculture; the Town Creek Foundation; the Conservation Fund; and Audubon.

A computer model used by the state for planning purposes predicts water levels could rise 3.7 feet by 2100, according to the University of Maryland Center for Environmental Science.

At Blackwater, which has lost more than 5,000 acres of marsh since the 1930s, the water could encroach even more quickly because the land is also subsiding. Though uplands can become marsh as waters rise, the pace of sea-level increase is outstripping the ability of marsh to “migrate” or replace what’s lost. Every year, more of the loblolly pines dotting the 27,000 acre property disappear in what was once upland at Blackwater, and with them, many of the bird species that call the refuge home, including wild turkeys, brown-headed nuthatches and chickadees.

Transferring sediment to repair marshes and shore up land is a new concept in the Bay watershed, though it has been done in parts of Louisiana to gird against floods. It wasn’t necessarily Whitbeck’s first idea. But he came to it, he said with a smile, out of “desperation” a few years ago, as rising sea levels and a proliferation of invasive nutria were killing Blackwater’s most productive ecosystems.

In eight years of walking and driving through Blackwater, Whitbeck was familiar with the rapid saltwater inundation of the marshes, the dead trees and the disappearance of certain waterfowl and bird species, even as the refuge boasts one of the largest bald eagle populations in the Eastern United States.

The refuge had a robust eradication program for nutria, which chomp through the root systems at alarming rates. Marshes are self-sustaining ecosystems that build vertically, and move, as tidal mineral sediment builds and plant life remains. But even after much of the nutria population had been eradicated, these marshes couldn’t keep up with the sea level rise.

The loss occurs piecemeal, Whitbeck explained. Rather than losing a whole marsh at once, he said, he’d see what looked like potholes in once-contiguous stretches, which over time enlarged. If the refuge staff did nothing, what marsh remained would become open water, likely by 2050.

Curson noticed similar changes during his bird studies. And at the Conservation Fund, Erik Meyers, the nonprofit’s vice president, also was becoming worried. The fund has added 8,000 acres of land to the refuge through public and private funds, and that includes lands that will enhance the experiences of visitors to the nearby Harriet Tubman Underground Railroad National Historical Park, which is supposed to open this spring.

Without knowing the other was doing it, Curson and Meyers each submitted proposals to Town Creek for funding to help save Blackwater’s marshes. Town Creek’s executive director, Stuart Clarke, got Curson and Meyers together with Whitbeck, and the trio worked on a plan they call Blackwater 2100. They looked at computer models of how the marsh was migrating, and where natural sediment was building up.

“It was the most productive planning exercise,” Whitbeck said of the mapping effort. “We still use it on a daily basis.”

They knew they couldn’t save all of the marsh, but they thought if they looked strategically at a piece of the refuge, they might be able to save important habitat that could also make room for a new marsh to move and grow.

The marsh, Meyers said, is one of the special features of Maryland’s landscape, and once it goes, it doesn’t return. But, Myers said, this restoration is not just about nostalgia, or habitat. The Chesapeake Bay’s cleanup plan is counting on marshes, the kidneys of the rivers, to hold nitrogen and phosphorus. If they’re underwater, he said, “you have changed all of your calculations.” That means cities, sewage plant operators, developers and farmers will have to find other ways to reduce pollution that are potentially more costly and less effective.

Soon, Whitbeck said, they all agreed on what to do, but didn’t know how to do it. They called Albert McCullough, a veteran wetland engineer with Sustainable Science, LLC, based in Denton. Using bathymetry, mapping and site visits, McCullough figured out that the bend in the Blackwater River would regenerate sediment without requiring a hole be dug in the river. But still, the team needed to figure out key details. Would they be transporting the right kinds of sediment? Would the plants take root? How much of a thin layer was enough? What was the right ratio of water and sediment?

“It was a lot of calculations,” McCullough said. “There was quite a bit of ‘MacGyvering’ in the field.”

It’s too early to say whether the thin layering will work, Whitbeck said.

“One way or another, we’re going to learn,” he said. “We’re going to know how these marshes behave — and how to bring them back.”

As he watched the slurry land in the marsh, Curson scanned the sky for Blackwater’s famous inhabitants. He normally would be listening, but he can’t hear over the noise. He’s hopeful that saltmarsh sparrows will be back in large numbers soon, and that one day before long he will see a black rail in the marsh instead of a machine.

“This is the most valuable project I’ve worked on in my whole career,” Curson said. “To restore this marsh, and work with these partners, it’s just been extremely rewarding.”