The wetlands of the Chesapeake Bay are nurseries for blue crabs, striped bass, menhaden and other important species. The variety of plants in them absorbs pollutants like nitrogen that run off city streets and farm fields.
And they protect properties from flooding by stabilizing shorelines and absorbing storm water.
That led the scientists at the Smithsonian Environmental Research Center near Annapolis to wonder how global warming will affect those wetlands. So, back in 1987 they created the Global Change Research Wetland in a marsh off the Rhode River and transported it into the next century, using carbon dioxide, a heat-trapping, greenhouse gas, that has steadily increased in the atmosphere during the last century.
“These plants have been growing in a future atmosphere for over three decades,” explained Patrick Megonigal, a senior scientist at the research center. “This represents the world's longest-running climate change experiment, other than the big one that we're all involved in."
From a corner of the marsh, raised, narrow walkways take you from one experiment to the next. You can hear the low hum of a pump circulating carbon dioxide, vital to plant growth, to dozens of experimental chambers made of PVC pipe frames wrapped in clear plastic to block the wind. Native wetland plants like grasses and needle-like sedges poke out.
Megonigal said they receive “pure carbon dioxide in the air stream, enough to simulate the year 2100, the end of the century.”
The experiment uses more than a ton-and-a-half of CO2 a week, more than the Camden Yards concessions stands, according to the person who delivers a supply each week.
They’ve learned, Megonigal said, that elevated CO2 “causes the plants to become shorter, but more dense.”
While some of the plants are burying more carbon they also are slowing down flood waters and capturing sediment. That can help build up marsh elevation and protect the shoreline.
But then there's the sea-level rise. The Chesapeake Bay is a hot spot for sinking lands and rising seas and that's affecting the plants in different ways. Wetland grasses are drowning as sea-level rises.
“In this marsh at least, the grasses seem to be disappearing and that's because the marsh is getting wetter,” Megonigal said. “As sea level rates are increasing the marsh floods more and more often, which favors the sedges but not the grasses.”
He says communities around the Bay need to learn to live with the marshes to help them.
“In order to keep their footprint, they need to able to migrate inland,” he said, “which they can do as long as the edge of the marsh is forest, or agriculture, perhaps. But they definitely can't do it if the edge of the marsh is a wall.”
If you live at the water's edge and your property is washing away, Megonigal suggests a living shoreline. That’s a combination of rip rap or oyster shell and plants to hold the soil. But the real solution, he adds, is reducing greenhouse gas emissions, the biggest of which is CO2.
“Our data show that the elevated CO2, which this marsh is experiencing, can actually help a little bit, but it can't solve the problem. The only real solution is to stabilize the rate of sea level rise. This marsh just can't survive but so much.”