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.
