You are here

Salt Marshes At Cape Cod National Seashore Being Squeezed Out Of Space

Share
Alternate Text
An example of high marsh dieback at Cape Cod National Seashore, taken near Great Island/NPs-Stephen Smith

Ever so gently, but steadily nonetheless, development and sea-level rise are slowly squeezing salt marshes at Cape Cod National Seashore. High marshes are being being transformed into low marshes, and low marshes are in danger of being drowned out.

"The vegetation communities have changed dramatically," says Stephen Smith, a plant ecologist at the seashore. "The shift in communities, the important part of that study, shows you have a loss of a certain type of habitat because it'™s being replaced by another one."

In a paper that examines the problem, Dr. Smith notes that between 1984 and 2013 more than 190 acres of high marsh vegetation have been lost due to sea level rise, while at the same time more than 130 acres of low marsh have been created. Though his study focused on just six salt marshes within the national seashore, the results point to an ecological dilemma that could have significant ramifications for flora and fauna at the seashore, though more research is needed to quantify those impacts.

"We're not really sure how that will influence the ecosystem," said Dr. Smith during a phone call last week. The high and low salt marshes contain "completely different species of plants, and as result they have completely different productivity, and nitrogen cycling and biomass and decomposition, and soil accretion, which helps marshes keep up with sea-level rise. So all those things are very different. It'™s a very complex question as to how that'™s going to change all the other elements of the ecosystem.'

But in the long run, he said, 'œThat low marsh itself will start to disappear if it cannot keep up with sea-level rise. And the projections of sea-level rise suggest that it will not be able to keep up.'

The two types of marshes attract, and are relied upon, by different collections of flora and fauna. As a result, the impacts will vary between the marshes. Birds and reptiles could suffer from a decline in the high marshes, while insects could be lost from both high and low marshes. At the same time, some crabs appear to be contributing to the downfall of some high marshes by feeding on vegetation.

'œA lot of the high marsh is used by birds and small mammals that need that ecotone between the high marsh and the terrestrial environment to forage in. So you'™ll find small mammals and various reptiles like snakes, black racers, and things like that," he said. "And then the low marsh, it'™s based really on the fact that it'™s flooded most of the time. You'™ll have large populations of mummichog (a type of killifish). There'™re various insects that kind of inhabit the two types of marsh. And then you have the plants themselves. The high marshes are distinct community of plants. Those are disappearing.'

Down the hall from Dr. Smith's office, Bob Cook, the seashore's wildlife biologist, said there haven't been any studies on how the transformation in marshes was impacting birds, animals, and fish.

"What I understand is happening is we'™re losing the upper marsh, the spartina alterniflora portions of the marsh, and those would be habitats where things like saltmarsh sparrow nest and forage," said Dr. Cook. "So I would expect that a species like the saltmarsh sparrow, some of the migrating shorebirds like whimbrel and some of the other peak species that typically favor that portion of the salt marsh, are going to be the ones that would be adversely affected by the loss of that portion of the salt marsh.'

According to data collected by Dr. Smith, between 1984 and 2013 sea-level rise along the saltmarshes has averaged 5.52 millimeters per year, which "is more than double that predicted based on the long-term rate of 2.63 mm/year in Boston."

The transformation of high marsh to low marsh was not uniform in the areas of the national seashore the ecologist studied. Pleasant Bay near Orleans, for instance, lost 146.7 acres of its high marshes, while Hatches Harbor near Provincetown lost just 2.8 acres. Conversely, Pleasant Bay gained 147.2 acres in low marsh, while Nauset Marsh near the Salt Pond Visitor Center at Eastham lost more than 52 acres.

Alternate Text
Another example of dieback, near Wellfleet/NPS-Stephen Smith

While Dr. Smith has not done similar surveys of marsh transition at other national seashores, there is concern that rising oceans will impact not just marshes but the wildlife and sea life that depend on them.

"Most of the birds unique to salt marshes face threats that place them on one or more conservation listings," the Maryland-DC chapter of the Audubon Society noted in its 2011-12 salt marshbird survey. "Seaside Sparrow and Clapper Rail, though abundant in suitable habitat, are on the American Bird Conservancy/Audubon WatchList. Saltmarsh Sparrow, much less common than the Seaside, is a WatchList species also listed as globally Vulnerable by Birdlife International, and Black Rail, now very rare in Maryland, is listed as Endangered in the state and considered by Birdlife as globally Near-threatened.

"The preeminent threat facing these birds is sea-level rise. Sea levels in Maryland have risen 1 foot (30cms) in the past century, contributing to significant marsh loss at Blackwater National Wildlife Refuge. This rate is projected to accelerate..."

At the Saltmarsh Habitat and Research Program, scientists not that, "Tidal marshes form the dominant transition zone between terrestrial and marine communities in eastern North America.  The eastern North American coast alone possesses over one-third of the global extent of tidal marsh and the highest level of vertebrate biodiversity and endemism (those species found in one location and no where else) of any tidal marsh region worldwide.  These wetlands are home to 83 breeding vertebrate species, 22 percent of which occur only in tidal marshes or possess subspecies found only in tidal marshes (Greenberg and Maldonado 2006). Tidal marshes are therefore primarily a North American resource, and it is a primary North American responsibility to conserve the ecosystem'™s global flora and fauna."

Furthmore, the group notes that, "Tidal marshes are also threatened by sea-level rise.  Over the last century sea level has risen ~2 mm/year (although local effects vary: Douglas 1991), and this change has altered marsh vegetation and caused marsh loss across the Atlantic seaboard.  Sea-level rise is projected to accelerate over the next century with predicted tidal marsh losses of 0.5-1.5% each year (Greenberg 2006).  Small sea-level increases could push tidal marsh bird populations to a threshold beyond which rapid declines are likely."

Back at Cape Cod, Dr. Smith said the transformation between high and low salt marshes is being driven both by sea-level rise as well as development that prevents high marshes from migrating higher in elevation as tidal flows rise.

"We have infrastructure now. It (a barrier to movement) can occur naturally, because low marshes butt up against very steep-sided dunes so they can'™t go anywhere, based on the natural topography. But in a lot of cases it'™s a road or a housing development," said Dr. Smith "We'™ve cut off their ability to migrate landward. The comon term used to describe that phenomenon is 'living squeeze.''

But at a time when this squeezing is going on, there are efforts to recover lost marsh habitat. Some revolve around widening culverts to allow for the return of tidal flows into areas that once were marshlands, such as along the Herring River estuary near Wellfleet and Truro that was cut off from normal flows in 1908 when dikes were constructed at Chequesset Neck and Duck Harbor. Those led to forest and other vegetation to take over the marshlands. Now talks are under way between the national seashore and area stakeholders to open up the tidal bottlenecks.

'œIt makes salt marsh restoration all that more important so we can alleviate some of those losses. It'™s happening all over the place; salt marsh restoration, putting in new culverts or competely opening up systems that were tidally restricted," the ecologist said. "We'™ve had two other sites that we'™ve done here on Cape Cod, Hatches Harbor and East Harbor. Hatches Harbor in particular has been greatly successful. We'™ve created something like 60 acres of restored salt marsh. The Herring River project is huge. The restricted flood plain is something like 1,100 acres. We could get a lot of recovered salt marsh out of there." 

 

Add comment

CAPTCHA

This question is for testing whether or not you are a human visitor and to prevent automated spam submissions.

Image CAPTCHA
Enter the characters shown in the image.

The Essential RVing Guide

The Essential RVing Guide to the National Parks

The National Parks RVing Guide, aka the Essential RVing Guide To The National Parks, is the definitive guide for RVers seeking information on campgrounds in the National Park System where they can park their rigs. It's available for free for both iPhones and Android models.

This app is packed with RVing specific details on more than 250 campgrounds in more than 70 parks.

You'll also find stories about RVing in the parks, some tips if you've just recently turned into an RVer, and some planning suggestions. A bonus that wasn't in the previous eBook or PDF versions of this guide are feeds of Traveler content: you'll find our latest stories as well as our most recent podcasts just a click away.

So whether you have an iPhone or an Android, download this app and start exploring the campgrounds in the National Park System where you can park your rig.