ROWLEY — For years, scientists have observed a slow decay of salt marshes all along the Atlantic coast without understanding why.
Now a newly released study conducted in the local Great Marsh, which extends from Gloucester and Essex in the south to Hampton, N.H., in the north, is shedding light on the cause of salt marsh decay and the impact it could have on the environment.
Scientists from the Marine Biology Laboratory, a nonprofit biological research group based out of Woods Hole, have determined that higher levels of nutrients such as nitrogen and phosphorous are contributing to the widespread decay of salt marshes along the east coast.
The group, led by MBL scientist Linda Deegan, has been introducing nitrogen and phosphorous into a portion of Sweeney Creek in the Plum Island Estuary since 2003, and the group announced last week that significant decay in the experimental area has occurred as a result. The creek is located near the Rowley/Ipswich line in a remote section of the marsh.
“We have known that we’ve been losing marshes in places like Connecticut and Long Island and Delaware, but we haven’t really understood why,” Deegan said in a video interview her team posted on YouTube. “On the basis of this experiment, we’re beginning to understand that at least some of that marsh loss is probably due to this widespread coastal nutrient enrichment from upland development.”
Over the course of nine years, the scientists added nitrogen and phosphorous to the tidal water flushing through the marsh’s creeks at levels typical of nutrient enrichment in densely developed areas, such as Cape Cod and Long Island, they said.
The scientists found that the higher level of nutrients caused the grass on the banks of the tidal creeks to grow taller while their roots grew shorter. As the grass grew taller, it eventually drooped over into the water, where the currents started pulling on it.