Day 65: CO2 boost to aid wetlands in climate change?

Wetlands illustration. Credit: Victoria Parks in Australia

Ever since I was exposed to information about human-caused environmental problems, in college, I’ve remained generally horrified — sometimes vaguely, and other times acutely — about the runaway train that is our collective effect on our planet. Moments of peace have shone through. One such moment was sparked when I read David Quammen’s book “Song of the Dodo,” for example, because it gave me a comforting image of Earth as durable host of a progression of creatures through time, and a faith in nature’s course that preceded us and will outlast us. 

This time, relief comes from a study that suggests nature as we know it can find small ways to adapt to us. 

One of the feared consequences of global warming is the widespread drowning of wetlands as the seas continue to rise. Whereas global oceans used to rise about a millimeter (0.039 inch) per year, they’ve been rising about three times that (just over 1/10 inch per year), overcoming modest swaths of wetlands each year around the world.

The Stikine River wetlands in southeast Alaska. Credit: Carr Clifton/Minden Pictures/Getty Images

Sea level rises have more to do with thermal expansion than glacial melt, but both factors are expected to increase along with carbon emissions. One might expect that wetlands would fold at catastrophic rates, taking with them all their charms: our commercially important fisheries, wildlife habitat, and wetlands’ two-way buffering abilities — which filter out human toxins in one direction and save us from the full brunt of the ocean’s power in the other.

But a new study, led by J. Adam Langley of the Smithsonian Environmental Research Center in Maryland and Villanova University, in Pennsylvania, reports that wetlands may be making a secret weapon from the very cause of all the trouble: the carbon dioxide itself.

Photo courtesy of Ducks Unlimited

Langley and his co-authors, from the Smithsonian Institution and the U.S. Geological Survey, made their discovery by adding carbon dioxide gas to a Maryland tidal marsh. For two years, the gas flowed continuously from the bottom upward through the top of large (two-meter diameter) cylinders surrounding marsh plots. And a funny thing happened — the marsh grew by just enough to withstand rising seas — about 3 mm (1/10 inch) a year. Root thickness also increased, which could also help the marsh withstand rising seas.

“Our findings show that elevated CO2 stimulates plant productivity, particularly below ground, thereby boosting marsh surface elevation,” Langley said in a press release.

Added Patrick Megonigal, a study-co-author and colleague of Langley’s at the Smithsonian Center, ”We found that by stimulating root growth, thus raising a marsh’s soil elevation, elevated CO2 may also increase the capacity for coastal wetlands to tolerate relative rises in sea level.”

The authors present their findings with a grain of salt: Although marshes appear to benefit from carbon dioxide in the short-term, the increasing levels will continue to warm the Earth, melt glaciers and expand ocean water, thus accelerating sea-level rise. Ultimately, rapidly rising seas could outstrip the positive effects of carbon dioxide on the marshes they have observed, they say.

Photo credit: Galveston Bay Estuary Program

“Wetlands are some of the most specialized and valuable ecosystems in the world, not only to wildlife but humans as well,” Megonigal said. “The sooner we can understand the effect global warming is having on them, the better we will be equipped to save them. Our next step is to determine whether this will continue in the long-term and in the face of actual sea-level rise and other climatic changes.”

The team’s findings were published last week in the Proceedings of the National Academy of Sciences. Some of this information comes from a Eurekalert press release.