Rising seas are drowning salt marshes

            The salt marsh at Audubon’s Shadblow Preserve on the Narrow River in Narragansett is wetter than it should be at low tide. Near the highest point on the marsh, Scott Ruhren stood nearly ankle deep in water, and shallow tidepools were unable to drain naturally, providing breeding habitat for mosquitoes. At the inland edge of the marsh, invasive phragmites were encroaching in areas where salt hay – a native plant that Ruhren said looks like the cowlick on a 10-year-old’s head – should be thriving instead.

            A few killdeer and Wilson’s snipe called loudly when they flew off at the approach of Audubon’s senior director of conservation, but little other bird life was noticeable in early spring, other than a few soaring gulls. It was a bad sign.

            “Just about every salt marsh in Rhode Island is having problems like these,” said Ruhren

Rhode Island salt marsh (Jake Zach)

of the 20-acre marsh property donated to the Society in 1974. “Our most obvious issue here is ponding of the water, rather than it draining, which is causing a switch-over in the plant community and a die-off of plants that can’t survive being constantly inundated.”

            Nearly all of the significant problems facing salt marshes in Rhode Island can be traced to rising sea levels – caused by melting glaciers and the thermal expansion of warming waters – and increasingly severe storms, both of which result in flooding and erosion of the habitat that serves numerous ecological functions.

According to Kenny Raposa, research coordinator at the Narragansett Bay NationalxEstuarine Research Reserve on Prudence Island, salt marshes are essential habitat for numerous species of fish and birds, and they absorb large quantities of carbon from the atmosphere. They also filter out pollutants and protect shorelines and property from damage caused by storms and waves.

            “Salt marshes require regular flooding with tidal waters, but it’s a delicate balance,” he said. “If they’re flooded too much, they drown and convert to open water. At high tide, essential nutrients are brought in for the plants. Low tide gives the marsh soils some time to dry out and provides access for birds and wildlife to use the marsh for feeding.”

            Raposa, who has been tracking the decline of salt marshes in Rhode Island for close to 10 years, said that sea level rise has led to the loss of almost 20 percent of the state’s salt marshes in recent decades, and the rate is accelerating.  His research has found that the salt marshes in the region are the most vulnerable in the entire country.

            “It’s happening right now, and it’s happening faster than I thought it would,” he said. “At normal rates of sea level rise, our marshes could keep pace as decaying plant matter and sediment deposits helped the marsh grow vertically at the same rate as sea level rise. But this just cannot happen fast enough anymore in our region, so the marshes are essentially drowning in place.”

            Salt marshes in the Northeast are growing through this accumulation of plant matter and sediment at a rate of 1.4 millimeters per year, while sea level has been rising 5.6 millimeters per year since 1999. It’s a trend that will only get worse. According to the National Oceanic and Atmospheric Administration, sea level has already risen about 10 inches in Rhode Island since 1930, and scientists predict it will raise two more feet by 2050 and seven feet by 2100.

            Raposa and Ruhren agree that the ideal circumstances would allow salt marshes to migrate inland as the waters rise. In some places that may be possible, though whether the marsh migration can keep up with the rate of sea level rise is uncertain. But most salt marshes in Rhode Island are faced with numerous barriers to their migration – roads and other developments constructed behind the marshes prohibit their inland movement, or the slope of the land limits how far they can move.

            “Even worse,” said Raposa, “new evidence shows that natural upland habitats like a forest can hold out longer than we thought and prevent marshes from migrating.”

            Other climate-related factors are exacerbating the problem. Warming temperatures may accelerate the breakdown of plant matter, making it more difficult for the marshes to grow in elevation to keep pace with sea level rise. And warmer winter temperatures allow fiddler crabs, which destabilize the soil with their burrows, to be active longer.

            One of the biggest losers from the flooding and loss of salt marsh habitat is the appropriately named salt marsh sparrow. The only breeding bird found nowhere else but on the East Coast of the United States, it is one of four local birds that breed exclusively in salt marsh habitat. (The others are the seaside sparrow, clapper rail and willet.) Scientists predict the sparrow will go extinct within the next 50 years.

            Research by University of Connecticut scientists Chris Elphick and Chris Fields has found that the secretive streaked bird with a pale orange triangle on its cheek has been declining by

Salt marsh sparrow at Jacob's Point, Warren (Evan Lipton)

about 9 percent per year since the late 1990s.

            “To put it in context, if your stock portfolio was declining at that rate, you’d be losing money fast. It’s pretty bad,” Elphick said. “About three-quarters of the population has disappeared.”

            Steve Reinert, a part-time ornithologist who has been studying salt marsh birds in Rhode Island since the 1980s, hasn’t observed a noticeable decline in the population of salt marsh sparrows yet, but he knows it won’t be long before he does.

            “Call me a pessimist, but I have little hope for this species,” said Reinert, a member of Audubon’s Council of Advisors. “It’s a species of global concern.”

            The problem the birds face has everything to do with the rising water levels in their breeding habitat.

            Salt marsh sparrows build their nests on the ground in areas of high marsh that typically do not get flooded except at high tide on nights with a new moon, which occurs every 28 days. It takes the birds that entire 28 days to build a nest, lay and incubate eggs, and raise nestlings to the point when they are able to make their first flight.

Reinert said that the birds’ first nesting attempt typically fails when it is flooded during the first new moon tide of the breeding season. But as soon as that happens, the birds start the process all over again and the nestlings typically fledge on the day of the next moon tide. Sometimes the young birds have to climb out of their nest and up an adjacent reed to avoid the rising tide on the last day or two before they are able to fly.

“Most of our successful nests get synchronized to the tidal cycle,” Reinert said. “All of the birds lose their first nest on the same night, and they all start building the new nest the same day.”

But as sea levels are rising, the birds are finding it more and more difficult to complete their nesting cycle before the high water returns.

“It’s already incredibly close for them without adding sea level rise. It’s always been touch and go,” said Reinert. “But now the whole balance of the equation is being thrown off, and they can’t afford to lose a day. The combination of a higher amplitude of tide and a potential shorter period to complete the nesting cycle can dramatically throw off this balance of nature. That’s where the devastation will come.”

            “It doesn’t take too much sea level rise to flip the switch for the birds,” added Elphick. “Literally, a couple inches can make the difference.”

            Unfortunately, little can be done to protect the birds in the long term, since any steps taken now to reduce sea level rise won’t have a practical effect until it’s too late. And while Elphick is exploring potential short-term fixes – like identifying the marshes that are least susceptible to the effects of sea level rise so they can be protected – he, too is pessimistic that the birds will last much beyond mid-century.

            While the outlook for the sparrow appears bleak, there are still numerous strategies that can be employed to preserve at least some of the salt marshes in the region. At the Sachuest Point and John Chafee national wildlife refuges, for instance, sand is being trucked in to raise the elevation of the marshes. Elsewhere, barriers to salt marsh migration, like old roadways, parking lots and other infrastructure, are being removed. And Kenny Raposa and others are experimentally testing the effectiveness of other ways of helping marshes survive the onslaught, from carefully digging channels into waterlogged sections of marshes to help them drain to seeking ways to help marshes migrate more quickly into adjacent uplands.

But deciding which marshes to protect and which to allow to disappear is difficult.

            Meg Kerr, Audubon’s senior director of policy, acknowledges that Rhode Island has a great deal to consider when setting priorities for responding to climate change, especially when it comes to sea level rise.

            “Resources are not endless,” she said. “So when it comes to salt marsh restoration projects, I’ve been making the argument that we need to step back, take a good look at where the best chances are for salt marshes to retreat and remain viable ecosystems, and make sure we’re investing in and prioritizing those sites.”

            She worries, however, that some in the scientific and coastal management community are inclined to wait for a better model or new evaluation tools before making these crucial decisions.

            “The tools we have now are good enough to tell us where the best options are for marsh migration,” she said. “There are lots of important players, including Audubon, who are already working together to implement salt marsh restoration projects, so let’s use the tools we have and keep going.”

            Using the national Sea Level Affecting Marshes Model, the Rhode Island Coastal Resources Management Council has mapped every coastal community in the state to identify the low-lying upland properties adjacent to salt marshes that may allow for future marsh migration. While the maps suggest that 80 percent of the state’s salt marshes will be lost from five feet of sea level rise – which would be expected to occur by the 2080s – marshes in upper Narragansett Bay appear to be less vulnerable than those along the south shore.

            According to Caitlin Chaffee, the CRMC policy analyst who manages the state’s Coastal and Estuarine Habitat Restoration Trust Fund, priority areas for salt marsh restoration will likely be based on marsh size, migration potential, those in important bird areas, and those containing rare sea level fen habitat. There are many potential intervention actions that can be taken at priority marshes, but she told attendees at the Rhode Island Land and Water Summit in March that “the fact that we’re already putting sediment on our marshes is an indication of how dire a situation we have. At first thought you’d think that marsh filling would be a serious no-no, but now we’re saying it’s a good thing.”

            While some scientists and coastal advocates are trying to put a positive spin on prospects for preserving salt marshes for the long-term, most appear to recognize that they are fighting a losing battle. Kenny Raposa, for one, finds hope from the many dedicated people, like Kerr, who are working together to try to figure out what can be done to preserve as many marshes as possible. But he also admits that he’s “quite pessimistic. I’m literally seeing and recording the loss of these marshes every year,” he said.

            Steve Reinert feels a similar sadness for what is being lost.

            “As a salt marsh researcher for 46 years in Rhode Island and southeastern Massachusetts, the thought of losing one of my favorite places, my favorite environments to walk and take people to and birdwatch in, is personally devastating,” he concluded. “I love the smell of the salt marsh, the prospect of a clapper rail running in front of you, fiddler crabs nipping at your toes. To think that the marsh may not even be there to walk any more is very depressing.”

This article first appeared in the June issue of Audubon Report, the newsletter of the Audubon Society of Rhode Island.