Climatide

Courtesy of Smithsonian Environmental Research Center

Chambers with elevated levels of carbon dioxide and/or nitrogen dot the landscape of the Global Change Research Wetland in Maryland.

BBC’s Jane O’Brien reports that the world’s longest-running man-made carbon dioxide experiment (other than the Earth itself) is providing insights into the conflicting impacts of carbon dioxide and nitrogen on coastal wetlands:

while increased carbon dioxide (CO2) is the biggest cause of global warming, it also makes some plants grow faster which builds new soil and helps the land keep pace with rising sea levels.

“That’s the silver lining,” says Patrick Megonigal, a senior biogeochemist at the Smithsonian Environmental Research Center. “CO2 acts as a fertiliser on some plants, and in a marsh like this, a faster growing plant has some good characteristics.

“This marsh can actually build soil through root growth and more soil means this marsh can rise upwards and therefore keep pace with rising sea levels.”

The marsh is dotted with atmospherically controlled chambers that contain the same amount of CO2 that the planet may be exposed to by the year 2100 – roughly double what it is today.

“They’re like time capsules. We are simulating the future inside them,” says Dr Megonigal. “We’re trying to travel forward in time by subjecting these plants to the conditions the whole world will be subjected to a hundred years from now.”

But there are other man-made factors that may counteract soil creation. Pollution – particularly from nitrogen – can have a major impact.

“We found that when you combine nitrogen with CO2, the positive effect on soil elevation is cut in half. So while increased CO2 helps the marsh keep pace with rising sea levels, increased nitrogen seems to work in the other direction. What you give with one hand you take with the other. It’s a very complex situation.”

A blog post on the Smithsonian Environmental Research Center site elaborates on the complexity, explaining that high carbon dioxide levels favor certain plants while high nitrogen levels favor others. It’s a trade-off. One that could determine the future of coastal wetlands.