Scientists in Maryland have transported parts of a marsh into the next century. They are looking at the future effects of global warming and increased carbon dioxide on wetlands around the Chesapeake Bay.
Wetlands are nurseries for blue crabs, striped bass and menhaden among other important species of the Chesapeake Bay. The variety of plants also absorb pollutants like nitrogen, that run off city streets and farm fields. And they protect properties from flooding by stabilizing shorelines and absorbing stormwater.
So back in 1987, scientists created the Global Change Research Wetland in a marsh off the Rhode River in Maryland to find out what global warming means for wetlands. "These plants have been growing in a future atmosphere for over three decades," says Patrick Megonigal, a senior scientist at the Smithsonian Environmental Research Center. "This represents the world's longest-running climate change experiment, other than the big one that we're all involved in."
We step from the woods out into a corner of the marsh, where raised, narrow walkways take you from one experiment to the next. The low hum is a pump circulating pure 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. "They receive pure carbon dioxide in the air stream, enough to simulate the year 2100, the end of the century," Megonigal explains.
To do that, a web of black cables out to the marsh connect the chambers back to the woods where six canisters of CO2, as big as two middle-schoolers stand outside a research station. The experiment uses over a ton-and-a-half a week, more CO2 than the Camden Yards concessions stands, according to the person who delivers a supply each week. So, what have they found? "Elevated CO2 causes the plants to become shorter but more dense," Megonigal answers.
So, while some of the plants are burying more carbon they are also 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 hot spot for sinking lands and rising seas and that's affecting the plants in different ways. Wetland grasses are dying as the sea-level rises. "In this marsh at least, the grasses seem to be disappearing and that's because the marsh is getting wetter. As sea level rates are increasing the marsh floods more and more often which favors the sedges but not the grasses."
So, what can communities around the Chesapeake Bay do to help wetlands? "In order to keep their footprint, they need to able to migrate inland. Which they can do as long as the edge of the marsh is forest, or agriculture, perhaps," Megonigal says. "But they definitely can't do it if the edge of the marsh is a wall."
And if you are living at the water's edge and experiencing erosion, he suggests a living shoreline, which is a combination of rip rap or oyster shell and plants. But the real solution is cutting green house 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," Megonigal argues. "This marsh just can't survive but so much."