New England salt marshes, like most coastal wetlands, face a lot of pressure: invasive species, roadway runoff, encroaching development and sea level rise.
But a study published Wednesday in the journal Nature suggests that sea level rise, at least, may offer a sliver of a silver lining.
By looking at soil cores from 345 locations around the globe, dating back thousands of years, scientists found a trend: Coastal wetlands can adapt to fast-rising seas by trapping more carbon in the soil beneath them.
This is good news for us. Scientists say to stave off dire effects of climate change, we humans need to pull excess carbon out of the atmosphere. And coastal wetlands, which include marshes, mangroves and seagrasses, store carbon more efficiently than forests. New England's salt marshes provide additional benefits, like filtering toxins from groundwater, and buffering houses from storm surges. And with sea level expected to rise up to 18 inches by 2050, it's also good to know that the marshes might be able to keep up.
But this "keeping up" only works to a point.
"There is a sweet spot in these coastal wetlands where a certain amount of flooding can actually help the marshes grow faster and sequester carbon at a higher rate, by allowing them to accumulate sediment," says study co-author Patrick Megonigal, a senior scientist at the Smithsonian Environmental Research Center. But too much flooding becomes "stressful," he says: The marsh plants drown, and die from a lack of oxygen.
So, says Megonigal, the plants need room to grow.
"They need to be able to move inland," says Megonigal. "But they can only do that if there are no obstructions to their migration, like seawalls, buildings, or other hard structures."
Anne Giblin, a senior scientist with the Marine Biological Laboratory in Woods Hole, who was not involved with the study, calls the work "interesting" but cautions that we shouldn't stop worrying about the effects of sea level rise on threatened marshes, and that increasing carbon storage in wetlands certainly won't solve our climate change problems. But she adds, this study "makes you think about value of these wetlands," and the services they provide.