Increasing levels of nutrients seeping from septic systems and lawn fertilizers may be driving the steady decline of salt marshes that has occurred along the U.S. East coast in recent decades, a new study has found.
While scientists had long believed that salt marshes have an unlimited capacity for removing nutrients such as nitrogen and phosphorus, a long-term experiment by researchers at the Marine Biological Laboratory (MBL) at Woods Hole, Mass. found that nutrient enrichment can drive salt-marsh loss. Over nine years, the researchers added amounts of nitrogen and phosphorus to tidal waters flushing through salt marsh in an undeveloped coastal area consistent with the nutrient levels present in developed areas such as Cape Cod, Mass. and Long Island, N.Y. Within a few years, they observed wide cracks in the grassy banks of tidal creeks; eventually, the researchers say, the banks would collapse altogether into the creek. “The long-term effect is conversion of a vegetated marsh into a mudflat, which is a much less productive ecosystem,” said Linda Deegan, an MBL scientist and an author of the study published in Nature.
David S. Johnson/MBL