Sea level rise is happening so fast that some of New Jersey’s key tidal marshes could be swallowed whole by next century, eliminating critical wetlands that serve as wildlife habitat and storm barriers, according to a recently published Rutgers-led study.
The study’s authors layout four potential ways to save the marshes: buying out homeowners who live at the edge of wetlands, allowing an invasive reed to spread, pumping layers of new sediment atop the marshes, or building experimental “living shorelines.”
“Faced with sea level rise, a marsh has two options — it can either increase its elevation at a rate equal to that of sea level rise, or it can migrate inland,” said lead author Judith Weis, a professor emerita of biological sciences at Rutgers-Newark. “Otherwise, it will be submerged and drown.”
The study was published this week in the journal Anthropocene Coasts.
In New Jersey, tidal marshes are those areas where the Atlantic Ocean and estuaries meet land. Key habitats for crabs, shrimp, birds and mammals, the marshes are also vital to soak up rain and prevent flooding during storms and surges. They absorb toxins, such as metals, and nitrogen to help reduce algal blooms. They also absorb carbon dioxide, a greenhouse gas and contributor to climate change.
The researchers looked at available data for four locations: the Meadowlands and Raritan Bay in North Jersey, and the Delaware and Barnegat Bays in South Jersey.
Weis said the team found it difficult to tease out the impact of sea level rise on the Meadowlands in Bergen County because there is so much human activity there including conservation efforts aimed at restoring wetlands, as well as intense development.
The authors found no change in acreage of tidal marshes around Raritan Bay, just south of Staten Island, between 1986 and 2015, but said solid data on the area are lacking.
But they did find significant loss of wetlands surrounding Barnegat Bay in Ocean County. The bay is fed by saltwater from the Atlantic Ocean through an inlet and mixes with freshwater sources, such as the Toms River. A previous analysis showed that about 12% of the bay’s tidal wetlands were lost between 1972 and 2012.
In highly developed areas, marshes often get trapped between the rising sea and infrastructure like buildings, roads, and developments, and simply can’t migrate inland.
The team found considerable erosion along Delaware Bay, where salt water from the Atlantic Ocean mixes with freshwater from the Delaware River. The bay is bordered by Cape May, Cumberland, and Salem Counties in New Jersey, as well as Sussex, Kent, and New Castle Counties in Delaware.
The study said that “most analyses suggest that Delaware Bay marshes are eroding and converting to open water” at a rate of 1.1% to 1.9% per decade.
However, Weis noted wetlands around the Delaware Bay have room to migrate, unlike many wetlands in North Jersey. Yet the migration creates other problems as higher concentrations of seawater move in behind the retreating marshes. Salt water is lethal to the globally threatened Atlantic White Cedar, for example.
“The salt water is coming in higher and higher with sea level rise, and that’s what’s killing those trees and creating so-called ghost forests,” Weis said. “As the marshes move inland, it’s converting forest into marsh. So the marshes gain at the expense of the forests.”
The state Department of Environmental Protection announced last month a 10-year plan to restore 10,000 acres of Atlantic white cedar forests to the state’s Pinelands region. The trees, which can live up to 1,000 years, have been killed off along streams in lowland swamps. In New Jersey, Atlantic white cedar once occupied over 125,000 acres. That’s fallen to less than 25,000.
The Rutgers’ study makes clear that sea level rise, the major force behind the loss, is not the only threat. Development, runoff, dredging, and other man-made activity contribute.
Parts of the coast are also naturally sinking due to geological reasons, which compound the effect of sea level rise.
The researchers said marshes can’t increase their elevation as rapidly as the sea is rising. They note that sea levels are expected to rise between 2 to 5.2 feet between the base year of 2000 and 2100 under a scenario of moderate greenhouse gas emissions. That rise would be steeper if greenhouse gas outputs remain high.
Sea level rise along the mid-Atlantic is already higher than the global average.
“If marsh acreage is reduced and coastal storms become more intense, coastal communities will lose protection and will be subject to greater storm damage,” the authors wrote. “Reduced areas of marshes, which are nurseries for some commercial and recreational fish, will likely also lead to reduced fish production.”
To reduce loss, the authors said municipalities could be encouraged to buy and demolish houses in order to prevent erosion. But Weis said the cost for such a “managed retreat” would be high and face political opposition. New Jersey’s Blue Acres program buys out willing homeowners in flood-prone areas, but funding is limited.
Another strategy would be to pump thin layers of sediment from nearby creeks onto the marshes. Experiments have shown promise, but Weis also said it’s also costly.
Installment of so-called living shorelines prevent erosion through the creation of oyster reefs, or barriers of shells, rocks, logs and other material constructed at a marsh’s edge to shield it from waves. Another costly option.
Weis said one promising — and cheap — strategy calls for halting the removal of invasive Phragmites. The reeds grow aggressively and outcompete native plants and pose threats to native wildlife. Land managers have programs to remove them with herbicides and replace them with native cordgrass.
However, Weis said reeds have shown to be good buffers, allowing marshes to elevate faster than they normally would because they create a protective layer when they die.
“This plant that has been viewed as a villain may be the way some marshes may be able to survive sea level rise,” Weis said.