What happens to a marsh when sea levels rise?

Plum Island Estuary in Massachusetts is called the "Great Marsh" by locals. The largest remaining salt marsh in the Northeastern U.S., it's a haven for fish, crabs, birds, plants and shellfish.

The marsh is also the center of an ongoing study. Plum Island is one of the National Science Foundation's Long Term Ecological Research sites. Scientists want to know how this 2,000 year-old ecosystem adapts to changes. Since 1998, biologists, chemists and ecologists have been documenting the swamp's response to land development and climate change — particularly, how it handles rising sea levels.

"So the big question is how will these marshes survive if sea levels rates really increase," says Anne Giblin, a biogeochemist at the Marine Biological Laboratory who is heading the study.

Rising sea levels means that the tide will wash brackish water farther into the wetlands, throwing off its balance of salty and fresh water. Marsh plants are used to a certain level of water. But at some point it's too much, Giblin says.

"You can imagine if these grasses are underwater several hours a day, there's very little oxygen down here," Giblin says, pointing to the roots. Some species seem to adapt, like the cordgrass. Others, like the saltmarsh hay, do not.

NewsHour science correspondent Miles O'Brien gets into the reeds for this story from National Science Foundation's series "Science Nation."*

*For the record, the National Science Foundation is also an underwriter of the NewsHour.

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