Day in and day out for 13 years, scientists slowly dripped fertilizers into a pristine section of salt marsh north of Boston. They were simulating, in a controlled experiment, the pollution that marshes in densely populated areas receive from sewage, lawn fertilizer, and other human sources.
By the time they stopped dripping the nutrients — nitrogen and phosphorus — in 2016, they had observed changes in the marsh’s plant and animal community and even in its physical structure.
The creek banks had begun to crack and slump down, indicating that the over the long term, nutrient pollution could be a factor in converting “a vegetated marsh into a mudflat, which is a much less productive ecosystem,” said MBL Fellow Linda Deegan, lead investigator of the project at the Plum Island Ecosystems Long-Term Ecological Research Site (PIE-LTER).
Losses of healthy salt marsh have accelerated in recent decades, with some losses caused by sea-level rise and development. “Salt marshes are a critical interface between the land and sea,” Deegan said. “They provide habitat for fish, birds, and shellfish; protect coastal cities from storms; and take nutrients out of water coming from upland areas, which protects coastal bays from pollution.”
Now, the team wants to know, “Will this marsh be able to recover?” Buoyed by a new, three-year grant from the National Science Foundation, they are watching how the marsh is responding now that the nutrient addition has stopped.
“We want to see how microbes, plants and animals respond to a decrease in nutrients,” said Anne Giblin, who directs the MBL Ecosystems Center as well as the PIE-LTER. “We will also see if the changes in the marsh’s physical structure that we observed after fertilization began will continue in the same direction, or reverse course.”
This marks the latest phase in the ecosystem-scale TIDE Project, which began in 2002. The scientists now hope to illuminate “the legacy effects of stress-induced changes (genotypic to landscape) on ecosystem recovery, and the limits of landscape resilience.”
Giblin received this collaborative NSF grant with Deegan, a senior scientist at Woods Hole Research Center, and James A. Nelson, assistant professor at University of Louisiana.
Top photo: Lush cordgrass (Spartina patens) at a salt marsh in Ipswich, Mass., part of the Plum Island Ecosystems study site. Credit: David S. Johnson, TIDE Project