Anticipating global warming, scientists measure the long-term effect of extra carbon dioxide on marsh

Great story from September 29th Baltimore Sun about CO2 research on marsh grasses being carried out
— for the past 23 years!!! — by researchers at the Smithsonian Environmental Research Center in Mayo. . . .

[See research by Bert Drake of SERC at Scientific Commons: <http://en.scientificcommons.org/bert_g_drake>]

Waist-deep in fieldwork

Anticipating global warming, scientists are measuring the long-term effect of extra carbon dioxide on marsh plants
By Timothy B. Wheeler

Baltimore Sun reporter

September 29, 2009

This lush marsh south of Annapolis seems like an alien landscape – clear plastic bubbles dot the watery plain, with curved white pipes poking, periscope-like, out of the tall, green grass.

The odd-looking structures spread across Kirkpatrick Marsh are providing researchers with a peek into Earth’s future, helping them understand how climate change could alter the world we live in.

For the past 23 years, Bert Drake and other scientists at the Smithsonian Environmental Research Center in Shady Side have been monitoring the growth of marsh grasses and plants encased in the clear plastic bubbles on the fringe of the Rhode River. Those patches have been fed a steady diet of air enriched with carbon dioxide – the gas scientists say is driving our climate toward irrevocable change as human activity spews more of it into the atmosphere.

What Drake and colleagues have found is good news, of a sort. These wetlands, which help protect the Chesapeake Bay from water pollution, might also offer some protection from the climate upheaval that experts expect to come with rising levels of carbon dioxide in the atmosphere.

Three-square, or scirpus olneyi, a sedge blanketing this salt marsh and commonly found throughout much of North America, grows thicker and faster as it’s fed more carbon dioxide, Drake says.

Scientists have known for quite a while that plants generally grow better when exposed to air with higher-than-normal concentrations of carbon dioxide. But some shorter studies suggested that the plants’ growth spurt would tail off after a few years. With funding at first from the Department of Energy and more recently from the U.S. Geological Survey, Drake and colleagues tested the long-term effects by piping carbon dioxide into chambers enclosing the marsh plants. The clear plastic allowed sunlight to penetrate, so plants’ photosynthesis was not affected. The researchers enriched the air inside to double the level of CO2 in the open air outside – about how concentrated the gas might be in the Earth’s atmosphere by the end of the century, Drake notes, given current increases from burning fossil fuels.

They compared the number and size of plants inside the chambers with patches of vegetation outside in the open air, and they checked the carbon-dioxide effect on another marsh plant, Spartina patens, or saltmeadow cordgrass, which is known not to respond to elevated levels of the gas.

Now, after more than two decades of tracking in the longest-running field study of its kind, Drake can say, “The bottom line is these plants have taken up a lot more carbon over the course of the study.” And they don’t become saturated.

Scientists have found similar responses in other plant communities. Drake and others have monitored a tract of scrub oak forest near Kennedy Space Center in Florida for more than a decade, and found the bushy trees also took off with a boost in carbon dioxide. Drake has been working recently with researchers setting up a parallel experiment in Norway on the edge of the Arctic.

But the Smithsonian scientist cautions that plants likely won’t save the planet from gorging on greenhouse gases. That’s because his research also has found that the marsh plants’ growth really is controlled by several factors – the most important being how much water they get.

“It depends very much on rainfall. If there’s no water, it can’t work,” he says of the marsh sedge’s tendency to act like a carbon sponge.

That could be a problem, because scientists predict that climate shifts could disrupt precipitation patterns in this region. Rain and snow might fall more heavily in winter and spring, climate models indicate, but less frequently, coming in big storms followed by dry spells. Moisture in soil and plants also is likely to evaporate more readily as temperatures gradually climb.

“It’s good news and bad news,” concludes Drake. “It’s great if the plants can take up CO2, but they may not be able to do that.”

Patrick Megonigal, one of Drake’s Smithsonian colleagues, has found similarly mixed news about the ability of marshes like this to cope with another climate-change impact – rising sea level.

Scientists have worried that as polar ice melts and the oceans warm, sea level will rise by several feet over the next century and could essentially drown wetlands, which serve as nature’s kidneys. They filter nitrogen, phosphorus and sediment out of water draining off the land before they can foul rivers and bays like the Chesapeake.

But Megonigal and colleagues have learned that the same carbon dioxide believed to be fueling rising sea levels might also help salt marshes outgrow rising waters – for a time, anyway. The extra greenhouse gas stimulates root growth, building up the surface of the marsh. Kirkpatrick Marsh apparently has managed to survive in this spot for thousands of years even though sea level has been slowly rising.

“It’s one of those silver lining stories,” says Megonigal, 50, a senior scientist. He notes that probes sunk into the muck beneath the marsh have found evidence it has risen in elevation by about 15 feet in the last 10,000 years, since the end of the last Ice Age.

“As sea level rose, this marsh, millimeter by millimeter, built its own soil out of dead plant material and rose 15 feet,” he says. He and his research team set up their own village of clear plastic chambers on the marsh to pipe carbon dioxide in to patches of vegetation, then carefully monitored the level of the mucky soil in which the plants were growing to see if, and how fast, it rose.

Four years on, they’ve found, as Drake’s longer study did, that giving the plants more carbon dioxide boosts the elevation of the marsh above sea level.

He cautions, however, that all types of wetlands may not respond the same way to increased carbon dioxide, and that even salt marshes such as this one might not survive if sea level rises at an increasing rate, as many project it will. A faster rise in the seas could outstrip the ability of the marsh to stay above water.

“This won’t eliminate the dangers of rising sea level for marshes,” he says. “It will only mitigate it.” He figures there’s a “window of opportunity” to curb the increase in sea level over the next several decades before it overwhelms the marsh’s natural buildup.

Should marshes like this go under, that could spell more trouble for the beleaguered Chesapeake Bay, since all the nitrogen locked up in the wetland soil and vegetation would be released into waters already choking on too much of the nutrient. That’s just one of the reasons why scientists have warned that climate change could complicate the effort to restore the bay.

“It’s a very complex picture,” concludes Drake, who at 73 is approaching retirement. He’s working now to get all the data archived from his 23-year experiment – archived so it can be carried on by other scientists. And he’s using the insights he’s gained from decades of studying climate-change questions to speak in public more about what’s known – and still uncertain – about how humans are changing the Earth.

Of one thing he’s certain – change is happening now. In the time since he began his study more than two decades ago, carbon dioxide levels in the air over the marsh have increased by more than 12 percent, and sea level there has risen by about 4 inches.

“We still don’t know what to say about how the effects of climate change are going to affect ecosystems,” he says, “but we’re starting to really worry.”

Copyright © 2009, The Baltimore Sun

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About Bruce

Work for sustainable development of small islands; ex-Peace Corps (Volunteer and staff) in LA & Caribbean; cruised Caribbean on S/Y Meander for three years; like small tropical islands, French canals, Umbria, Tasmania, and NZ. Married 50 years. Former President (1995 to 2016) of Island Resources Foundation.
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