Ecosystem on the edge

On a brisk and rainy autumn morning at a salt marsh in Newmarket, New Hampshire, the rigid smell of brine and seaweed assaults the air, punctuated by sulfurous odors of decomposing matter. Rain falls over a bed of tangled reeds and grasses, adorned by the occasional shell of a horseshoe crab, or a minnow that did not quite make it out with the receding ocean. Wind slaps at salty veins of water creeping through the marsh, the sea carrying in nutrients with each breath of tide.

Unseen, a small yellow-cheeked sparrow hides among sprigs of smooth cordgrass. Aptly named the saltmarsh sparrow, this secretive and skulking bird is found only in salt marshes from the Atlantic and Gulf coasts, and breeds on a thin strip from Maine to Virginia.

The seldom-spotted sparrow’s quiet call sounds something like a shy red-winged blackbird trying to imitate R2-D2. But these whispered calls are at risk of being silenced.

Researchers that monitor the nesting success of sparrows have too often been met with an unpleasant site: wet masses of feathers, remains of drowned chicks that did not stand a chance against cold seawater.

Global warming may make the problem more common. As the earth is trapped beneath a blanket of fossil fuel emissions, less and less heat escapes back to space. Glaciers at the poles melt with the increase in temperature, and the excess water runs into the oceans. As rising ocean levels shift the coastline, tidal marshes may not be able to migrate inland fast enough.

A model for the towns of Seabrook and Hampton predicts that, with a six-foot sea level rise by 2100, nearly all of the towns’ current marshes would be turned to mudflats.

The saltmarsh sparrow is already declining at a high rate of nine percent per year, according to a study by Maureen Correll and colleagues published in the journal Conservation Biology in 2016. At such a rate, the sparrow could be down to just 500 individuals in 50 years. That fate will only worsen if marshes disappear as quickly as projected.

“They should be the poster bird for climate change,” said James Taylor, professor of general ecology and ornithology at the University of New Hampshire.

The nine percent loss of these birds per year is mainly from habitat loss and degradation from human construction and will be increased by sea level rise. These birds are a symptom of a much bigger problem, and their loss may indicate the illness of an entire ecosystem.

Salt marshes trim New Hampshire’s shoreline in areas where the ocean collides with freshwater rivers. Tides bring sediments into the marsh area, where they are trapped by plant roots and stems as the water recedes. The levels that the tides reach create zones of the salt marsh. These zones fall into two categories: high marsh and low marsh.

The high marsh is flooded only intermittently by exceptionally high tides that occur about once a month, while the low marsh is flooded regularly by the daily tides. These two separate zones have their own unique composition of flora and fauna.

But now the seas are rising and tides are changing. New Hampshire’s sea level has the potential to rise between 39 and 55 inches, according to a study conducted in part by Cameron Wake, a UNH professor of glaciology and climatology.

“Sea level rise is the most obvious threat facing salt marshes today” said David Burdick, professor of wetland ecology at UNH.

When marshes flood more than usual, they collapse. The high marsh along the bank of the creek falls in, and the whole elevation of the marsh goes down.

Marshes build up this elevation at a natural rate per year, which is why they have been able to keep up with sea level rise for thousands of years. Eleven thousand years ago, New Hampshire’s coastline was nine miles further out to sea, close to the Isles of Shoals. But it is unclear how quickly marshes can react to accelerated flooding.

“We know that marshes have the ability to migrate, but what we do not know is how fast they are able to rise” said Burdick.

Tidal restriction is another potentially lethal factor. Tides bring sediments to the marsh, and sediments build the marsh up in elevation. When this exchange is cut off by a road or other construction, the marshes lose their ability to keep up with sea level rise.

Adrienne Kovach, professor of conservation genetics and researcher of the saltmarsh sparrow at the UNH, says that how marshes will respond to sea level rise is not fully understood.

Some studies contend that marshes are not as endangered as people say. These scientists reason that many analysis methods fail to take into account the marsh’s ability to migrate, and do not consider a possible increase in the rate the marshes collect sediments. However, this is only true for marshes with unrestricted tidal flow, as stated in a study by Matthew Kirwen and colleagues published in Nature Climate Change journal in 2016.

A study in Long Island Sound predicted that marshes will not migrate in the near future. Researchers found trees taking root at the edge of marshes, a sign that the marsh is not migrating, according to a study by Christopher Field and colleagues published in Biological Conservation journal in 2016.

“Every marsh is a little bit different due to sediment source”, said Burdick, “but we do know that marshes have died because the sea level went up”.

All salt marshes in New Hampshire have been run through the Sea Level Affecting Marshes Model (SLAMM), according to Cory Riley, Reserve Manager for the Great Bay National Estuarine Research Reserve. These models compile data about how marshes are likely to shift, where a marsh will be lost, and where it could migrate based on elevation.

If the marshes have any chance of migrating inland and surviving, an effort needs to be made to make room for them. In many cases, roads and houses are in the way. When cut off from the ocean, the marshes are unable to get a constant exchange of sediments, which they need to remain healthy, and can turn into mud flats. Much of a salt marsh’s fate depends on the circumstances of each individual marsh and the rate of sea level rise.

As marsh hydrology changes, the species that depend on it will be affected. Only 25 species of vertebrate animals are able to spend their entire life cycle in a salt marsh. Living in such a harsh environment involves extreme specialization and specific adaptations. Just as an engineer could not do the work of a biologist, specialization means that these animals often cannot perform well outside of their niche.

The saltmarsh sparrow is an example of this. The birds have evolved the ability to synchronize their reproductive cycle to the tide cycle. Sparrows build their nests just 10-20 cm off the ground in high marsh areas that are flooded about once a month by a high tide. Sparrows build their nests, lay their eggs, and fledge their young between these high tides. They need a certain window of flood-free time in order to fledge their young, according to Kovach, who is currently at the forefront of research on this vulnerable species.

If a sparrow nests at the wrong time, the nest will be flooded by the highest monthly tide. When this happens, the bird is quick to re-nest. Since the re-nest is so rapid, the next monthly high tide should not happen again until the nestlings are fledged. But now these high tides seem to happen more often.

“We have seen over time that there has been more flooding, more nests lost to flooding, and an increase in storms,” said Kovach, “We can attribute that to climate change and sea level rise”.

Saltmarsh sparrows are not the only birds that would be affected by a loss of salt marsh habitat. Salt marshes are an important part of the Atlantic Flyway, a main corridor for bird migration along the Atlantic coast, said Sarah Flemming, head of conservation management on the Atlantic Coast for Ducks Unlimited.

Migrating birds need places to stop that can provide high-energy, and nutrient-rich food during their energy-expensive flights. A healthy and functioning marsh can ensure they have all their needs met, and these benefits are not limited to birds alone.

“More than one-third of the endangered species list rely on wetlands to survive,” said Chris Sebastian, head of public relations for Ducks Unlimited. Salt marshes and freshwater wetlands are considered critical conservation areas.

Salt marshes were recently included in a wildlife action plan for the state of New Hampshire. This means that they are considered important ecosystems to protect for the conservation of the state’s wildlife. Town by town profiles have been made in coastal New Hampshire to illustrate how restoration of a salt marsh could benefit that community.

Benefits include pollution filtration, long-term carbon storage, flood mitigation, storm protection, and healthy fisheries – all of which are a natural way to buffer against climate change.

Projects to raise the elevation of the marsh, called “thin layer sediment deposition,” use sediments that were dredged from nearby areas to spray onto the marsh to help build up its elevation. These projects have been successful in Maryland and Rhode Island for salt marsh restoration and could help the marshes outpace sea level rise in the future.

The Nature Conservancy in Lubberland Creek in Newmarket, New Hampshire has proposed widening a culvert to, among other goals, allow for the salt marsh on their reserve to migrate with sea level rise by providing a pathway for tide-water to flow further inland.

Thin layer sediment deposition, as well as removal of tidal flow restrictions, have been successful in returning native plant species to the marsh and regaining sediment flow.

Unfortunately for the saltmarsh sparrow, it may not be that simple. The species did not rebound in restored salt marshes as expected, but declined, according to a 2015 study by Chris Elphick and colleagues published in the journal Restoration Ecology.

More nests were flooded in the restored marsh sites because high marsh vegetation, which is critical for the sparrow’s nesting success, did not come back. It also appears that tidal restriction was actually providing some relief from flooding. The study found no evidence that high marsh vegetation would return within the next 20 to 30 years. Even marshes that were restored decades ago are not suitable habitat for saltmarsh sparrows.

The conundrum remains: tidal restriction provides a nesting refuge for the sparrow, but makes the marsh far less likely to keep pace with sea level rise.

Solutions to help this little sparrow are in the making, but none have proved successful. One proposal by UNH graduate student Bri Benvenuti and colleagues is to install floating islands of habitat. Like a floating garden of native salt marsh plants, the islands would raise and lower with the tide, providing flood-free nesting areas for the sparrows. Four of these islands have already been constructed at Rachel Carson National Wildlife Refuge in Wells, Maine.

Floating habitats are still in the pilot stages for the saltmarsh sparrow, but show promise. They have proved successful for other bird species like the common loon and rails. Saltmarsh sparrows are currently listed as “vulnerable” by the International Union for Conservation of Nature (IUCN) Red List version 2016-2. Yet the bird’s status is coming under review by US Fish & Wildlife to consider an “endangered” state listing under the Endangered Species Act.

Much of the research for the new review comes from SHARP, the Saltmarsh Habitat & Avian Research Program, a group of academic, government and nonprofit working to protect coastal birds. SHARP researchers have spent summers banding sparrow nestlings, conducting “point-count” surveys, and even fitting the birds with “nanotags” – tiny backpack-type apparatuses with antennas to track migrations.

An endangered status would require a detailed conservation plan be made for the preservation of the species. But that will be complicated by rising seas, and the uncertain impact climate change will have on salt marshes.

“If there is one bird that is going to get hit, it’s this one” said Taylor.


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