Meadowlands shown to be valuable for pulling carbon dioxide from the air
Scientists had already known that the plants in rural wetlands pull carbon dioxide — a harmful greenhouse gas — from the air. But new research being conducted in the Meadowlands shows that even degraded urban wetlands are able to capture and store carbon pollutants, providing a valuable resource to combat climate change.
The results are significant because urban wetlands are located in the very places where more carbon dioxide gets released into the atmosphere — heavily populated industrialized centers with a concentration of cars, factories and power plants.
The ongoing Meadowlands research shows that, even though urban wetlands have been disturbed by development and pollution, the plants that thrive there capture carbon dioxide out of the atmosphere and store it in the marsh floor for hundreds of years — far longer than an upland forest can.
“Scientists had not known a lot about how the urban, temperate wetlands performed before,” said Karina Schafer, an ecosystem ecologist at Rutgers University, who oversees the research in coordination with Princeton and other universities.
Carbon dioxide is one of the greenhouse gases that trap heat in the atmosphere, exacerbating global warming and the effects of climate change. President Obama recently cast a spotlight on the idea of capturing and storing carbon dioxide — also called carbon sequestration — when he called for new rules that would require power plants to capture the carbon they emit when burning fossil fuels, such as coal and gas. Industry officials have said there is still no technology that can do the job on a commercial scale.
But the Meadowlands wetlands have been engaged in a natural form of carbon sequestration for thousands of years.
Since 2009, the Meadowlands Commission has gathered measurements to learn how much carbon dioxide gets pulled out of the air by plants in the wetlands along the Hackensack River. Plants also release carbon back into the atmosphere, but the research shows that they capture more than they emit — and that when the plants die and fall into the muck, the carbon remains encased in the Meadowlands soil.
“We are finding that our wetlands here are net sinks of carbon,” said Francisco Artigas, director of the Meadowlands Environmental Research Institute, the commission’s research arm. “This is another reason why we should preserve the wetlands we have and restore those that have been damaged. They are providing a real ecological service in the metro area.”
For some time, experts have studied the potential for investors to preserve and restore wetlands, then recoup the costs and even turn a profit by selling credits for carbon storage. Potential buyers of the carbon credits might be entities such as power plants, which emit carbon dioxide and might some day be required to either reduce their emissions or buy carbon credits to offset the emissions. The U.S. Geological Survey has researched the feasibility of “carbon-capture farming,” in which farmers convert their agricultural land to wetlands specifically to sell carbon credits.
A similar concept already exists, in which wetlands are restored and credits are then sold to developers or transportation agencies whose new projects and roads destroy some wetlands. One of these mitigation banks is already operating in the Meadowlands.
The research showing how well wetlands capture and store carbon could add new impetus to the concept of restoring wetlands and then selling carbon credits. “It bodes well for the concept,” said Andrew Baldwin, a wetlands plant ecologist at the University of Maryland.
The Meadowlands research was started with $40,000 from the commission; since then, Schafer and her collaborators at Princeton and other universities have secured about $800,000 in grants from the National Science Foundation for the work, which includes a variety of projects.
Results will be detailed in a paper submitted to the Journal of Geophysical Research: Biogeosciences, Schafer said.
An urban wetland such as the Meadowlands has to handle many stresses, from their use as dumps for garbage and debris to encroaching development and pollution in their waters. The Hackensack River winds through the Meadowlands, and at any given time, from 40 percent to 60 percent of the river’s flow is made up of treated wastewater, Schafer said. Wastewater contains nitrogen, which scientists are finding can cause wetlands to collapse.
Despite such stresses, the research has found that the wetland area under study traps 213 grams of carbon per square meter, Artigas said. That means in a year, the 31-acre site stores nearly 27 tons of carbon.
Using a 3-D anemometer and an optical carbon dioxide sensor, the researchers measure air speed and direction down into wetlands plants and up and away from them, as well as the varying amounts of carbon dioxide in the air.
The project also involved coring down 17 feet to get 3,600 years of soil data, which showed that 78 percent of carbon dioxide captured by the wetland remains trapped after 130 years, while 50 percent remains sequestered after 1,700 years.
The core sampling, though, doesn’t necessarily reflect the geology of the entire Meadowlands, since some areas have been disturbed or restored, and once-captured carbon is removed or released in the process, Schafer said. Even Superstorm Sandy scraped away some sediment, causing more captured carbon to be released, she said.
In addition, restored wetlands may emit more carbon than they capture for several years until the plants become well established, Schafer said.
Schafer said that when the native salt marsh cordgrass called spartina is growing in stands by itself, it tends to be more productive at capturing carbon than when it is competing with phragmites, an invasive species. “When both types of plant are present, they each have less productivity than when in a monoculture stand of either one of them,” she said.
Phragmites, though, does a better job capturing carbon than spartina does, Schafer said. And while her research has shown that phragmites emits methane — an even more potent greenhouse gas than carbon dioxide — it captures so much carbon that its net impact in an urban wetland is positive.
Baldwin said sea levels drop cyclically, and when they do, the organic matter in the soil of a wetland tends to oxidize more quickly, reducing the amount of carbon sequestered. Ironically, sea levels are rising in New Jersey in part because of the impact of climate change, and so the marshes in the state will have a greater net capacity to store carbon because they will be able to accumulate more organic matter.
On the other hand, he said, if the sea level rises too quickly, it would outpace the ability of the marsh to build up vertically, and the plants would succumb to oxygen stress caused by excessive flooding and waterlogged soil.
Wetlands are generally better than upland terrain at storing carbon because wetland soils are depleted of oxygen and it takes dead plant matter far longer to decompose, which keeps the carbon trapped longer, Baldwin said. Upland trees also capture carbon dioxide in their leaves, but when the leaves fall, oxygen and bacteria in the soil break them down quickly, releasing the carbon back into the air.
“These are interesting findings,” Baldwin said of the Meadowlands study. “They seem to provide good quantitative evidence of carbon sequestration in coastal wetlands. As long as the wetland continues to build plant detritus, it will continue to remove a net amount of carbon from the atmosphere.”
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