From Nautil.us, April 21:
The Challenge of Blue Carbon
A year on from Hurricane Katrina, the small Louisiana town of Luling, about 25 miles west of New Orleans, embarked upon a modest experiment. Instead of discharging treated municipal wastewater through a canal and into a nearby lake, the town would pump its effluent into surrounding bayou swampland.
The change would be a small step in reversing the ecological damage of flood control along the Mississippi River, which for centuries had slowly separated America’s longest river system from its natural floodplain. Although it opened up more land for farming and habitation, flood control set the scene for the levee failures in New Orleans, where more than 1,000 people died in Katrina and its aftermath. Preventing natural seasonal flooding also deprives the Mississippi delta of sediments that renew it, contributing to the loss of 30 percent of its land in the past half-century.
A mangrove swamp might contain 25 times as much carbon as a similar patch of terrestrial forest.
In Luling, sediments that would have flowed directly into the lake would now be trapped in the town’s bayous. Nitrogen, phosphorous, and other chemicals in the cloudy wastewater would enhance the growth of native bald cypress and water tupelo trees. These in turn would soak up floodwaters, prevent erosion, and provide crucial ecosystem services. The trees would be a boon for wildlife: Bald cypresses serve as breeding grounds for amphibians, provide nesting spots for ducks and raptors, and shelter young catfish among their submerged roots.
On top of all those benefits, the revitalized swamp would store lots of carbon—at least in principle. In practice, it wouldn’t be so simple.
So-called “blue carbon” aquatic ecosystems like Luling’s bald cypresses, Australia’s seagrass meadows, and tropical tidal marshes store an estimated 300 billion tons of carbon worldwide—an amount roughly comparable, by some estimates, to the lifetime emissions of all the power plants in the world. A mangrove swamp might contain 25 times as much carbon as a similarly-sized patch of terrestrial forest.
These capacities have made wetlands appealing targets for the fast-growing, near-trillion-dollar carbon accounting industry, which uses carbon offsets and carbon credits to—hopefully—reduce global CO2 emissions. Each offset or credit is supposed to represent an actual ton of CO2 sequestered or prevented from entering the atmosphere. To ensure that happens, the science behind them, and oversight of the projects that generate them, must be rock solid. This is far from certain today, where even the largest schemes have faced accusations of shoddy measurement, weak verification, and outright fraud.
“There’s a lot of bogus carbon projects out there,” says Robert Lane, chief operating officer at Comite Resources, the coastal science consultancy behind the Luling project. “Real carbon projects take an area of land and do something to it so it sequesters more than it would without intervention. And it’s that extra sequestration that you can monetize.” But monetizing Luling’s swamps would prove tricky.
In September 2012, the 600 hectares of Luling’s wastewater wetlands became the first blue carbon project approved by the American Carbon Registry (ACR), a private non-profit greenhouse gas registry. Over the next 40 years, its credits would be sold to pay for ongoing carbon monitoring costs and to compensate the bayou’s owner, a private real estate and development company, “We calculated that the area would sequester 11,617 tons of CO2 each year,” says Lane. “If the price of carbon were $20 a ton, which is a reasonable market price, that would generate $232,340 per year.”....
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