Salt marshes have been flooded by inland freshwater along nearly a third of the U.S. Atlantic coast, due to diversions by dams, dikes, and other human constructs. This hurts more than the natural biodiversity of a saltwater system. As salt marshes freshen, they emit more and more methane—a powerful greenhouse gas.
“A molecule of methane is 30 times more potent as a greenhouse gas than a molecule of carbon dioxide,” says Jim Tang, an associate scientist in the MBL Ecosystems Center.