Elevating Drowning Salt Marshes

While many coastal residents are seeking measures to protect their homes from a rising sea and increased flooding, one is quietly losing its bid on coastal real estate and could disappear forever.

Saltmarsh Sharp-tailed Sparrow strictly nests in Spartina Patens meadows.

Saltmarsh sharp-tailed sparrow strictly nests in Spartina patens meadows.

The saltmarsh sharp-tailed sparrow, a small, stocky songbird with an orange-yellow face, is a secretive bird that can easily go unnoticed—even more so as populations decline. It is currently listed as “vulnerable” by the International Union for Conservation of Nature and Natural Resources Red List (IUCN).

“They’re predicting the collapse of the species in 20 years,” said Caitlin Chaffee, c
oastal policy analyst for the R.I. Coastal Resources Management Council (CRMC), referring to findings from Saltmarsh Habitat and Avian Research Program during the Coastweeks Narrow River Tour earlier in October. “It puts a point on the problem.”

The problem, loss of salt marsh, is due to various factors including sea level rise, increased flooding, recreational boating that accelerates erosion along marsh banks, and increasing populations of marsh crabs that are consuming marsh grass and also increasing erosion rates.

“This is what saltmarsh sparrows like to nest in,” Chaffee said, pointing to a large patch of Spartina patens, also known as salt marsh hay. “And that’s what we’re losing right now.”

Salt marsh hay, a slender and wiry plant, is considered a “high-marsh” species as it is set back from the water’s edge and is flooded at times by high tides. But these plants, as well as others, are slowly being lost or found in unexpected places.

“We’re noticing high-marsh areas losing vegetation or transitioning to low-marsh vegetation,” said Chaffee, explaining a shift in plant zonation where species that would normally be near the water are now being found within the marsh interior and in high-marsh zones and vice versa. 

Caitlin Chaffee shows how standing ponds impact salt marshes along the Narrow River.

Caitlin Chaffee shows how standing ponds impact salt marshes along the Narrow River.

Many pools and salt pannes have developed throughout the Narrow River marsh interior because of water not draining properly at low tide, but fortunately they have not expanded and some have even started to revegetate over the last year, according to Chaffee, as a result of runnels, or “micro-creeks,” that were developed to drain pools and get standing water off the marsh. 

“Sea level rise is accelerating, particularly in the Northeast,” said Chaffee, adding that Rhode Island is a hotspot above the global average with over 4-millimeter annual increase over the last 30 years. “Marshes are usually resilient [and] build elevation as sea level rises, but in Rhode Island, marshes sit low in the tidal frame and don’t have the elevation capital.”

Keegan_TLD

Experimental thin layer depositions (TLDs) along the Narrow River intended to fill in flooded areas and build up marsh elevation.

Water on the marsh, as well as eroding edges exasperated by wakes from recreational boaters and herbivorous crabs, are still a problem, she says, because the salt marsh has lost its ability to maintain elevation. Chaffee explained that the Narrow River has very little sediment, so she hopes thin layer depositions (TLDs) to fill in and replant degrading areas will build a stronger shore. Thin layer depositions from dredged sediments in the center of the Narrow River (operations expected to begin this November) will be sprayed onto salt marsh surfaces to restore damaged areas, as well as to enhance the marsh’s ability to withstand sea level rise. The dredged sites will also be used to restore eelgrass beds.

“It’s a delicate balance: too little deposition won’t buy the marsh much more time in its lifespan because sea level rise is outpacing marsh accretion,” said Danni Goulet, marine infrastructure coordinator for CRMC, in a press release. “Too much deposition and Phragmites would soon populate the marsh.”

In an area like the Narrow River, Phragmites, a common salt marsh reed, is generally a cause for concern due to its ability to take over habitat, but is less of threat due to sea level rise.

Phragmites is good at a few things; it builds elevation and builds these enormous rhizome systems that will build its own mats that can expand out into open water. It’s a lot of biomass and takes up a lot of nutrients. In terms of nitrogen removal it’s a powerhouse,” said Chaffee. “From our agency standpoint, we don’t advocate for getting rid of it everywhere, especially in our urban, more developed areas, because it definitely serves a function. Areas that won’t ever be restored to a pristine salt marsh, we feel it definitely serves some functions and has value. In an area like the Narrow River, we’re concerned that it’s displacing habitat. We’re probably never going to get rid of that fringe but the thought is that it’s going to be kept at bay by tides.”

DCIM102GOPRO

Oyster bags are used for “Living Shorelines”

Other restoration efforts include The Nature Conservancy’s “living shorelines.” These incorporate oyster bags and coconut fiber coir logs under the eroding marsh bank to protect shoreline by breaking up wave energy from boaters.

“The idea is to incorporate natural materials that are really friendly to the environment, that plants and animals like, and that in the future this marsh edge will grow out to encompass, and eventually completely obscure, the coir logs so that you won’t even know that we were ever here,” said John Torgan, director of ocean and coastal conservation at the Nature Conservancy to Rhode Island Public Radio.

Several homeowners have requested applications to apply such means on their properties.

“Where we have marsh in front of properties, typically shoreline hardening is prohibited, but we have gotten requests to use soft materials to reinforce a bank,” said Chaffee, noting that the state is considering such applications, and adding that coastal resiliency projects like these are often contracted out to Massachusetts companies and could be a potential market for Rhode Island-based companies.

Monitoring will continue for these projects as dredging projects are expected to be underway this winter.

“The Narrow River project is vital to the success of this and future marsh restoration projects, using thin layer deposition techniques to increase the elevation of the salt marsh,” said Grover Fugate, executive director of the CRMC, in a press release. “This project will serve as a pilot for others, and different methods will be explored to determine which is most successful.”

Dredging and re-use of dredged material for marsh restoration is planned for Ninigret Pond as part of the salt ponds restoration project, according to CRMC, which received $3.25 million for coastal wetland restoration and planning within the salt ponds region in southern Rhode Island, specifically within Ninigret, Quonochontaug, and Winnapaug ponds. 

 


 

Meredith Haas | Rhode Island Sea Grant Communications