The waterways of New York City are famously dirty: They’re full of everything from cigarette butts to runoff from wastewater treatment plants. Fish and plants are literally choked out as algae, which thrive in the nutrient-rich waters, use up all the available oxygen. Now, a team of scientists has found a possible solution, using tens of thousands of mussels to vacuum up excess nutrients from part of the Bronx River Estuary. A floating raft stocked with the marine bivalves could remove about 60 kilograms of nitrogen from the water each year, they suggest, and a flotilla of hundreds of rafts could make meaningful improvements to water quality in urban areas.
The new results are “exciting and promising,” says Odd Lindahl, a marine ecologist at the University of Gothenburg in Sweden who wasn’t involved in the research. “Shellfish aquaculture has a great potential for … improving coastal water quality.”
The team—which includes marine scientists, a commercial mussel farmer, and volunteers from a New York City–based youth development program—spent several exhausting days collecting nearly 32,000 adult ribbed mussels from the salt marshes and mudflats of Jamaica Bay in New York City. Ribbed mussels, once plentiful before many marshes were paved over, are a natural choice for scrubbing the Bronx River, says team member Julie Rose, a research ecologist at the National Oceanic and Atmospheric Administration Northeast Fisheries Science Center’s Milford Laboratory in Connecticut. They’re native to the region, and they dine on bacteria and phytoplankton, which absorb excess nutrients like nitrogen and phosphorus. And scientists wouldn’t have to worry about human poachers: Ribbed mussels aren’t on the menus of fine restaurants because they produce a chemical that gives them a terrible taste.
Using dissolvable cotton thread, the researchers attached some of the finger-length mussels to submerged nylon ropes and placed the rest in mesh bags hanging off a specially built raft. The floating platform, measuring 6 by 6 meters, was then anchored just downstream from the Hunts Point Wastewater Treatment Plant, a facility that pumps out an estimated 830–1600 metric tons of nitrogen a year.
Six months later, the researchers retrieved 30 of the mussels, dried and ground their tissues, and measured the levels of nitrogen in the mussel powder. Extrapolating the results, the researchers estimated that the 32,000 mussels had likely removed about 6 kilograms of nitrogen from the water, they reported last week in Environmental Science & Technology. That would mean a fully stocked raft of mussels—about 338,000 animals in all—could potentially sequester more than 60 kilograms of nitrogen in their tissues, shells, and bodily fluids. That’s a small dent in the yearly nitrogen discharge of Hunts Point, the scientists acknowledge, but hundreds of rafts could make a real impact.
Setting up flotillas of mussels might be harder than it sounds, however. The team couldn’t coax young larval-stage mussels to populate the raft, so they had to collect adult mussels from a nearby salt marsh destined to be drained. Such “vacuum cleaner” mussels would also need to be periodically replaced. “When mussels are younger, they incorporate more nutrients into their tissues because they’re growing faster,” says Eve Galimany, a shellfish biologist and team member from the Milford Laboratory. Not so with older mussels. But instead of going to a landfill, those old-timers could be used to make chicken feed, Galimany suggests. “The whole point is to recycle nutrients.”