A nine-year study conducted in the Plum Island estuary indicates that sewage and fertilizers may be seriously damaging salt marshes. The study, published in the journal Nature, indicates salt marshes may be crumbling from the inside out, due to polluted waterways and runoff from people’s lawns. It’s a concern because the marshes are critical to protecting young marine life and absorbing the ocean’s pounding. As part of the study, researchers from the Marine Biological Laboratory Ecosystems Center regularly dumped fertilizer into a section of the salt marsh. Fertilizers and sewage contain phosphorus and nitrogen, which can accelerate the breakdown of plants and cause algae to bloom that suck oxygen out of water. The experiment has researchers worried about the future of salt marshes, which are already pressured by rising sea levels.