Blue Carbon

The reason for mangroves’ massive capacity for carbon can be summed up in two words: perpetual wetness.


October 15, 2014

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By Lee Sherman Gellatly

LOOKING THROUGH J. BOONE KAUFFMAN’S PHOTO COLLECTION is like thumbing a tropical bestiary. There’s a proboscis monkey from Borneo, its long, lumpy nose resembling an over-ripe mango. A gibbon and an orangutan from Kalimantan. A green python coiled around a tree. A herd of bristle-nosed pigs. A 15-foot saltwater crocodile whose jaw could crush a cow’s skull. A fruit bat wrapped in paper-thin wings, translucent and webbed. A mudskipper (a fish that uses its pectoral fins to walk on land, like some evolutionary trailblazer from the primordial ooze). Then there’s the Bengal tiger — its footprint, anyway. Kauffman, an ecosystem ecologist at Oregon State University, found the five-inch diameter print smack-dab on top of the boot print he had left in the Bangladeshi mud just hours before.

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Welcome to the mangroves rimming the tropical oceans of the world. The Indonesian archipelago boasts fully a third of the world’s mangroves — swampy forests of saltwater-tolerant vegetation where the land meets the sea. But they exist all over the tropics and subtropics. Recognizable by their tangled “pneumatophores” (spidery “stilt roots” that protrude from the soil and support a thick, green canopy overhead) mangroves occur in Liberia, Senegal, Gabon, Mexico, Cambodia, Thailand, Brazil and some 120 other countries, including the United States.

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It’s in these places where Kauffman plies his science — places rife with rare and predatory animals, parasites and venomous insects, mud “up to your thighs,” foliage so dense you have to “squirm your way through,” humidity that wraps around you like a steamy towel and tides that never relent. He and his team measure the mangroves’ stored carbon. They also guide local people toward studying and conserving these uniquely rich ecosystems for their own livelihoods, as well as for biodiversity and greenhouse gas mitigation.

“Mangroves are among the most carbon-dense forests in the tropics,” says Kauffman, who discovered the remarkable carbon-holding power of mangroves and other tropical wetlands while he was studying typhoon damage in Micronesia more than a decade ago. In fact, he says, mangroves are the penultimate “carbon sinks” (places that absorb more carbon and other greenhouse gasses than they release), in some cases holding onto five times as much carbon as upland forests long known to be important carbon storehouses. In 2011, Kauffman and post-doctoral researcher Dan Donato were among the first scientists to document the phenomenon in a Nature Geoscience paper titled, “Mangroves among the Most Carbon-Rich Forests in the Tropics.”

The reason for mangroves’ massive capacity for carbon can be summed up in two words: perpetual wetness.

“When you have a completely saturated environment of high tides twice a day, the soils are always wet and, in th tropics, always warm,” he says, “so they’re slowly accumulating carbon all the time.” The soil carbon comes from organic matter — the roots, trunks and leaves of plants and trees that constantly add to the rich organic matter stored in the saturated soils. In contrast to upland forests, which have carbon-rich soils only a few inches deep, mangrove soils typically hold huge quantities of carbon up to 10 feet deep or even greater.

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Kauffman works with and trains local scientists, land managers and students such as these in Gamba, Gabon, Africa, enabling them to further conserve, restore and sustainably manage their mangroves. (Photo: David Korte)

Because of the endless wetness associated with these “marine” forests, this form of sequestered greenhouse gasses has been dubbed “blue carbon” — blue for oceanic waters, for tides that surge through the mangroves, for rivers that flood these wetlands during the rainy season. In recognition of this watery carbon trove, the Intergovernmental Panel on Climate Change (IPCC) has added blue carbon to its short list of critical ecosystems for keeping greenhouse gasses in check. Kauffman, in fact, serves on an IPCC committee contributing the latest science on mangroves, saltmarshes and sea grasses as well as inland wetlands. Last year, he was a co-author on an IPCC report on the measuring, monitoring and reporting of wetland carbon stocks.

“For so long, wetlands were poorly represented in the IPCC,” says Kauffman. “Now there’s a growing recognition of the value of blue-carbon ecosystems, not only the mangroves in the tropics but also the saltmarshes and sea grass meadows that are important right here in Oregon.”

Peat swamp forests, another tropical wetland ecosystem, are the freshwater equivalent of mangroves, fed not by tides but by floods from nearby rivers. Like their saline counterparts, they’re carbon supersinks. “The peat swamp forests of Indonesia are the very largest carbon stocks of any ecosystem on Earth today,” says Kauffman. “Some of our OSU graduate students have measured peat soils that are more than 30 feet over there.”

Dodging Ebola by Days

Exotic fauna aren’t the only subjects framed in Kauffman’s camera lens. He also photographs villagers who live in the 25 countries whose mangroves he has studied firsthand. In one of those photos, eight Liberian men, their trousers soaked to the thigh despite thick rubber boots, perch on the protruding roots of a giant mangrove tree. The men are giving peace signs and fist pumps, alongside a grinning Boone Kauffman, who has been working with them on mangrove conservation measures. Their faces convey optimism, even joy.

A little girl in a Liberian village holds a fruit bat she killed with a slingshot for her family’s dinner. (Photo: J. Boone Kaufmann)
A little girl in a Liberian village holds a fruit bat she killed with a slingshot for her family’s dinner. (Photo: J. Boone Kaufmann)

But there’s another photo from the same Liberian village that haunts Kauffman: two little girls with solemn expressions, each holding a light-brown fruit bat by its wingtips. The pointy-eared bats, which the girls had killed that morning with slingshots, were destined for the kettle in this poor community where bush meat is a staple.

The photo was taken in late February, just days before Ebola broke in Liberia.

“Fruit bats are carriers of the Ebola virus,” says Kauffman as he looks at the girls’ serious faces glowing on his monitor at the OSU Department of Fisheries and Wildlife. He slumps slightly in his chair as he wonders aloud about the fate of the little girls — “the daughters I never had.”

As the world’s wetlands succumb to the chainsaw and the plow, villagers are seeing traditional sources of sustenance wither away. Commercial shrimp farms, rice paddies and palm oil plantations are displacing millions of acres of carbon-rich wetlands in Indonesia, Southeast Asia, Africa and South America every year. The shrimp farms often are abandoned after a few years, leaving nothing but scarred earth. Palm trees for oil — an ingredient in hundreds of consumer products from Ritz Crackers to Johnson’s Bodywash — are overtaking vast landscapes of centuries-old tropical swamp forests. A few commercial farmers and corporations profit from the converted lands. Meanwhile, orangutans and tigers slouch toward extinction. Villagers confront a dying way of life.

“Mangroves have been used for centuries by indigenous peoples for fish and shellfish,” says Kauffman. “They are keystone habitats for many marine fishes. When you convert a mangrove to a shrimp farm, you sever the link between the mangrove and the fisherman, whether he’s fishing for his familyor for the marketplace. You lose the mangroves, you lose the fish.

“These farm-raised shrimp are exported to the United States, to Europe, to Japan,” he continues. “Literally, we’re taking food out of the mouths of local people when we import these products. There are fishing villages in Southeast Asia that were sustained for centuries but are no longer viable because of the loss of the mangroves. Whole villages have been abandoned.”

SWAMP Funds

It’s a “double-whammy,” Kauffman says, when mangroves and other wetlands are destroyed. That’s because they serve a twofold purpose in mitigating global warming: short-term, they take carbon out of the atmosphere every day; long-term, they hold onto it for centuries. So when you hack it down, you not only free up stored carbon into an already carbon-loaded atmosphere, but you also kill the vegetation that has been absorbing Earth’s excess carbon since the Industrial Age began pumping out fossil fuel emissions in ever-faster fashion.

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Data source: United Nations Environmental Program – World Conservation Monitoring Centre, Cambridge, UK

Doing science in the mangroves is “like being a child in a jungle gym,” Kauffman says. “You have to crawl up and over and through stilt roots and pneumatophores — these large aerial roots — and sometimes you’re in mud up to your thighs. You wear old sneakers that you tie on your feet really tight so you don’t lose them in the mud.” Once inside the mangrove, he and his team establish plots where they measure above-ground biomass (live trees and woody debris) and then, using “allometric” equations (which help scientists predict biomass from characteristics like height or diameter), they estimate carbon content. To sample soils, the team uses a peat auger, a pipe-like device that brings up slender cores of mud that are then dried and analyzed for their carbon concentration.

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But there’s so much more to mangroves than the gasses they sequester. They buffer shores against storms. They support coral reefs with nutrients and energy. They filter pollutants. They burst with a unique biodiversity found nowhere else on the planet. They feed and shelter human communities.

Empowering local people to steward their wetlands is one of Kauffman’s prime missions. With funding from the Sustainable Wetlands Adaptation and Mitigation Project (SWAMP) of the U.S. Agency for International Development and the Kalimantan Wetlands and Climate Study (KWACS), he mentors villagers in the science and politics of wetland conservation. He, Donato and their Indonesian colleagues at the Center for International Forestry Research (CIFOR) have developed and published protocols for measuring, monitoring and reporting on mangrove forests, not only for other scientists but also for the people who depend on their biological bounty.

“The people we work with in the field, the people in small villages, recognize the value of their mangroves,” he says. “So do the land managers. And particularly the climate change negotiators who participate in the United Nations Framework Convention on Climate Change get it. No matter where we’ve gone in the world, we’ve been very warmly welcomed. It’s been a great collaboration between us and all the places on the planet where we’ve worked.”

Blue carbon is a planetary lifeline, argues Kauffman, who along with his CIFOR colleagues, is setting up a global network and database for sharing mangrove science.

“When you look at all the greenhouse gasses that are emitted into the atmosphere, about 50 percent stay in the atmosphere, about 25 percent are sequestered by forests, and about 25 percent are absorbed in the oceans,” he notes. “The oceans and the forests are doing us a great service by slowing down rates of climate change by sequestering so much of the anthropogenic greenhouse gasses that largely come from burning fossil fuels.

“Without the world’s oceans, without the world’s forests, we’d be in terrible shape.”

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CATEGORIES: Healthy Planet Marine Studies Initiative