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.