Battle With The Sea: Helping Salt Marshes Adapt To Rapidly Rising Seas

Mar 11, 2015

Rhode Island is losing salt marshes at an alarming rate. Scientists and coastal planners say this is one of the most pressing climate change impacts already facing the Ocean State. Salt marshes are critical fish and wildlife habitats that support the state's fishing and tourism industries. As part of our Battle With The Sea series, we're taking you to two marshes to learn what the state is doing to help them adapt to rapidly rising seas.

On any given day, Round Marsh in Jamestown would be relatively quiet, with birds and other wildlife teeming within its grasses and mudflats.

But on this day, a small industrial machine designed to scoop out mud travels back and forth across a stable section of the marsh. Save the Bay’s restoration coordinator Wenley Ferguson said this excavator is digging a creek to help drain excess water off the marsh. 

Al Gettman, the Rhode Island Department of Environmental Management mosquito abatement coordinator, operates a small excavator for a salt marsh adaptation project.
Credit Ambar Espinoza / RIPR

"So right now our goal is we’re kind of fixing the plumbing of the marsh," said Ferguson. 

Salt marshes are flooded regularly with tides. But due to climate change, these coastal wetlands are dealing with more water than they can handle.

“I’m standing right now [stomps her feet] in about oh, right now about 4 inches of water,” said Ferguson. “Now in the dead of summer, there wasn’t as much water in here, but with greater, higher [than predicted] tides and the increased rate of sea level rise, we’re seeing more salt water get into these upper areas of the marsh.”

You can find salt marshes near the coast, where fresh water meets salty water. They’re highly valued as water filters, wave and storm buffers, and nurseries for birds, fish and shellfish.

Over decades salt marshes have been weakened by things like pollution, dredging, manmade ditching, and invasive species. But rising sea levels and more intense rains due to climate change appear to be making things worse. All that extra water gets trapped and creates expanded areas of open water.

"I can kind of show you,” said Ferguson. “Oh yeah, I'm going down,” she said as she stuck part of her leg into a pool of water. “I can't feel the bottom and I'm not going to go further, because it's winter."  

Ferguson finds remnants of dead marsh grasses in the pool, evidence this marsh used to have a lot less water.

Save the Bay's restoration coordinator Wenley Ferguson finds fish swimming in a pool of water in an area near a salt marsh that used to be a cow posture.
Credit Ambar Espinoza / RIPR

Next, we check out an area where the marsh meets a cow pasture that used to be dry enough for cows to graze. "There are fish in this pool,” she noted. “Isn't that interesting?"

Ferguson can tell saltwater from those higher tides and rising sea levels are making their way here, not just because of the fish she’s found, but also because of the salt-tolerant marsh grasses growing here. 

Over a short period, these expanded pools of water degrade the marsh's vegetation and make its soil unstable, with the potential for the marshes to sink and drown in place. Nearly half of Rhode Island’s salt marshes are at risk for drowning.

A little further down the coast in Narragansett, Caitlin Chaffee, stands near another marsh along the Narrow River. “So we're basically where the Pettaquamscutt River meets the ocean at Narragansett beach,” said Chaffee.

Chaffee, a policy analyst with the Coastal Resources Management Council, said salt marshes have historically kept up with the pace of sea level rise as it grows in height by trapping silt and sediments brought in from the tides.

“And also from the plants that die and decompose,” said Chaffee. “That material accumulates on the marsh surface… and it also builds the elevation of the marsh.”

Credit Courtesy of the Coastal Resources Management Council

Salt marshes typically grow in elevation at a rate of 2 to 3 millimeters per year. But the rate of sea level rise is faster than that: 4 millimeters per year. “So basically, sea level rise is starting to outpace the marshes ability to adapt,” said Chaffee.

Chaffee said marshes could expand inland in the future by migrating, or moving back, as the sea levels rise, but “you need a gentle slope,” said Chaffee. “It [the shoreline] needs to be undeveloped, landward of where the marsh exists now. And for much of the shoreline at least in Rhode Island, that's not really the case. We have a lot of coastal development, and we have a lot of steep topography.”

The Narrow River illustrates that conflict. The salt marshes on both sides of the river will eventually run up against steep topography and coastal development.

But there is a low-lying area next to the marsh that looks promising. The town of Narragansett bought this land and is working with partners, like the CRMC and Save the Bay, to protect it. You can already see that land is changing as the marsh moves in. 

A forest next to the marsh at the Narrow River is changing as the marsh looks for a place to build up elevation. Some shrubs are dying and trees are starting to get stressed. But scientists say this maritime forest is actually giving the marsh a place to move into - an opportunity to survive. That’s not the case for many marshes across the state.
Credit Ambar Espinoza / RIPR

But Chaffee cautions that’s not the outlook for many marshes across the state. And that’s a danger to the animals that depend on marshes for food and shelter.

“Many species spend part of their life cycles in salt marshes: fish, birds, but there are certain species that are actually need salt marshes to nest and breed,” said Chaffee. “And we're in danger—if we lose the habitat, we are in danger of losing those species.”

Losing our marshes would also hurt our economy, because they support the state’s fishing, tourism, and recreational industries.

That's why the excavator back at Round Marsh in Jamestown is digging small creeks to help drain the marsh. Then it will spread the dug up mud and dead plants across the marsh. Save the Bay’s Wenley Ferguson said that’ll get rid of pools and cut down on mosquitoes.

“It’s all exposed mud right now and it doesn’t look that beautiful,” said Ferguson. “Next spring, we’ll start to see re-colonization, more plants coming through this mud.” More plants growing through the mud means the marsh's soil will become stronger, more stable, and more elevated, so that it can keep up with rising sea levels. 

The project at Round Marsh is a partnership among many groups, including the town of Jamestown, the state Department of Environmental Management, and Save the Bay.
Credit Ambar Espinoza / RIPR

Scientists are hoping to shore up more marshes, like they’ve done here at Round Marsh. Rhode Island was the first state, followed recently by Connecticut, to develop statewide maps that show which salt marshes are in danger under different sea level rise scenarios. Those maps are called the Sea Level Affecting Marshes Model (SLAMM). Ferguson said the maps give interested groups an idea about where to focus the efforts.

“We want to be able to track those changes,” said Ferguson, “and then also try to determine:  what can we do to allow these marshes to adapt, so they can be as healthy and functioning as they can in light of sea level rise.” 

Different marshes will call for different adaptation techniques.

Even with the help of these projects, it’s hard to know whether these salt marshes will be around in 50 years. Will they build up quickly enough to keep up with rapidly rising seas? Or will these marshes transition to other types of habitats, like mudflats or more open water? We don’t know yet, but Ferguson said helping marshes adapt to climate change is worth trying.

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