On Virginia’s far Atlantic flank, a cherished store of salt marshes is being lost
A boat anchored off Smith Island, a barrier island off Virginia’s Eastern Shore, in November 2020. (Sarah Vogelsong/Virginia Mercury)
NEAR SMITH ISLAND — On a still day, floating in a flat-bottomed boat in the waters that stretch like sheets of glass between the mainland and the barrier islands off Virginia’s Eastern Shore, it’s hard to believe anything in this corner of the world has ever changed at all.
For centuries upon centuries, you could believe, this region has been nothing more than vast horizontal expanses of water, grasses and sky, held together by thin strips of land. Here is home to an endless cycle of tides, schooling fish, great migratory sweeps of birds pausing to rest as they come and go on their long journeys between the Arctic and South America.
But that sense of a world set off from time is an illusion. One of the greatest ironies of Virginia’s Eastern Shore is that its aura of timelessness is made possible only by ceaseless change. It’s the constant shifting of the barrier islands and the salt marshes behind them that have shielded the area from lasting human encroachment. Now, though, the marshes have run up against a human intrusion much harder to escape: climate change. As increasing global air and ocean temperatures accelerate the movement of the barrier islands landward, the Eastern Shore’s salt marshes are disappearing faster than they can rebuild themselves, leaving the mainland more vulnerable to rising waters and increasingly violent storms.
“These land masses have been responding to these forces for thousands and thousands of years,” said Alex Wilke, a coastal scientist with the Nature Conservancy’s Volgenau Virginia Coast Reserve where many of the salt marshes lie. But, she cautioned, “the pattern that we’ve seen in the past isn’t necessarily the pattern we’re going to see in the future.”
An ecosystem that thrives amid change
A type of coastal wetland, salt marshes are uniquely adapted to a life in flux. Because they lie in intertidal zones, they must be able to thrive both when covered by salt water and when bare.
“These are plants that are highly evolved to handle flooding,” said Matt Kirwan, a researcher with the Virginia Institute of Marine Sciences who studies how coastal landscapes, including those on the Eastern Shore, evolve. “In some cases, the marsh plants become more productive when they’re inundated with seawater.”
Spartina is one such plant. This tall, spiky grass, green in the spring and summer and fading to golden brown as the year wanes, is what dominates the Eastern Shore’s marshes. Along with underwater eelgrass, which was wiped out in the 1930s and is now returning with the help of conservationists, spartina serves as both nurse and nursery to dozens of species that call the intertidal zone their home.
Its protection also extends to humans. Spartina’s extensive root system helps trap and stabilize sediments, and when the plant multiplies and spreads, its flexible bulk absorbs the force of waves sweeping toward shore. It’s this buffering effect that scientists are talking about when they refer to the role salt marshes play in shielding the coastline from flooding and erosion.
“They’re really important in helping coastal communities be resilient to climate change because they absorb flooding waters,” said Karen McGlathery, a professor of environmental science at the University of Virginia and the lead investigator of the Virginia Coast Reserve Long-Term Ecological Research Project, which has been studying the region for more than three decades. Without that buffer, she added, “you’d have much more economic and social damage, much more impact on people and infrastructure.”
The limits of resilience
The grasses are, of course, only one of the primary building blocks of the salt marsh. The other is the barrier islands that fence them off from the sea.
Off Virginia’s Eastern Shore, some 14 of these narrow strips of sand act as the outer ring of defense against the turbulent Atlantic. Salt marshes are able to form because of their shelter, and as the surf carves away at the barrier islands’ outer edge, causing them to migrate toward the land, so too do the marshes.
“The islands are always moving. Inlets open and inlets close; that’s normal,” said Bo Lusk, another coastal science at the Volgenau Coast Reserve and a native of the Eastern Shore. But, he said, “the pace at which it’s happening now might not be natural.”
Scientific data back that up. One 2017 study that Kirwan co-authored found that between 1850 and 2010, barrier islands retreated an average of 5.1 meters (16.7 feet) per year. The rate rose to nearly 20 meters (65.6 feet) between 1980 and 2010. That movement of the barrier islands, the researchers contended, is responsible for the “majority” of marsh loss on the Atlantic side of the Eastern Shore.
“They are shrinking in size because the islands are eroding faster than the marshes are able to migrate,” said Kirwan. He’s seen the changes in his fieldwork: “The systems that I think I know well, I might not have been there for three months and they look completely different,” he said. “Sometimes just even trying to find our sample sites that we’ve been to for long periods of time, they’re hard to find because the place has changed so much so quickly.”
Lusk, whose family has deep roots on the Eastern Shore, can easily point to major alterations in the landscape that he’s seen unfold: A long arm of the state-owned Wreck Island lost in Hurricane Isabel in 2003. And, more recently, a chunk of Cobb Island lost in a nor’easter that has led to a strong new inflow of water into the intertidal region.
The latter is “probably one of the most dramatic shifts we’ve seen,” said Coast Reserve Director Jill Bieri. It’s also already caused problems: several shell reefs constructed by the Nature Conservancy near a shoreline have since been destroyed. The Conservancy has also turned to oyster castles, a type of concrete block used to build reefs, to help stem increased erosion after the loss of the Wreck Island spit.
As the speed with which the barrier islands move and break accelerates, the marshes that lie behind them are coming under growing stress.
“Marshes can deal with a certain amount of climate change and storm impact, but they can also reach a tipping point beyond which they can’t keep pace with sea level rise,” said McGlathery.
Hurricanes are one of the natural culprits at which Shore residents point the finger. And indeed, scientists have charted strong links between rising global temperatures and an increase in the severity of storms. But research on the Eastern Shore recently revealed a surprise: When it comes to marsh loss, it’s smaller, more frequent storms that seem to be having the greatest impact.
“From the marsh’s perspective, it’s not those big storms (that have the greatest effect), because they’ll just overtop the marsh,” said McGlathery. “It’s the small ones, the nor’easters and the more frequent smaller storms that are beating up against the marsh and causing the erosion.”
Like her colleagues, she emphasized that the migrations and erosion now unfolding in the Atlantic salt marshes are nothing new. What’s changed is their speed.
“It’s a completely natural process,” she said. “But it used to be that you would see it maybe in a small area. Now it’s happening faster, and we’re seeing it more widespread.”
A carbon sink in the watery lagoon
Another irony of the marshes: The proliferation of carbon in the atmosphere that has put in motion the gradual chipping away of the Atlantic salt marshes could actually be partially offset by the very marshes themselves.
Like forests, salt marshes are capable of absorbing the carbon dioxide that is one of the primary contributors to climate change. They have other advantages: in particular, they store carbon in the soil, where it tends to remain trapped for long periods of time. In contrast, trees store carbon in their woody biomass, so when they die, the carbon is released back into the atmosphere more quickly.
“On a per area basis, marshes sequester carbon in their soils on a rate that is more than an order of magnitude faster than a terrestrial forest,” said Kirwin.
The drawback? There are far more trees on Earth than there are marshes, which occupy only about 2 to 3 percent of the planet’s surface.
Nevertheless, policymakers have increasingly begun to incorporate marshes into their efforts to reduce carbon. In 2015, UVA scientists including McGlathery developed a protocol for including salt marsh and other tidal wetland restoration projects in carbon offset markets. This “blue carbon” framework has been adopted by Verified Carbon Standard, now known as Verra, a nonprofit that evaluates and certifies carbon reduction programs.
Virginia lawmakers have shown an interest in the possibility. During the 2020 regular session, the Eastern Shore’s Sen. Lynwood Lewis, D-Accomac, put forward a bill that would allow the Virginia Department of Environmental Quality to participate in carbon trading markets that include credits for the restoration of underwater grasses. Gov. Ralph Northam signed the measure into law April 7. Within the Chesapeake Bay, where marshes are less threatened and have kept their gains and losses in balance, marshes are also increasingly being incorporated into local governments’ portfolios of nature-based solutions to adapting to rising sea levels.
To Kirwin, the salt marshes of Virginia’s Atlantic edge, lying as they do along the longest expanse of wilderness that remains on the East Coast, are a unique advantage the state has in adjusting to sea level rise.
“We have lots of rural low-lying land that’s prone to flooding and has big marshes near where people live,” he said. “If you look at other places in the U.S. like the northeastern parts of the U.S. or if you look at other countries like China and most of the developed countries in Europe, it’s actually a pretty unusual setup.”
This story has been updated to reflect that the Cobb Island opening destroyed several shell reefs, not oyster castles.
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