Innovative Ways to Improve Water Quality

Traditional methods to reduce nutrients in the Sound include upgrading sewage  treatment plants to eliminate reactive nitrogen in sewage and reducing storm water runoff that carries nutrients from fertilizer and animal waste into storm drains and tributaries. These methods reduce the amount of nutrients entering the Sound from the land. An additional method that is being explored by managers is called “nutrient bioextraction,” in which nutrients are removed from within the Sound by the cultivation and harvest of organisms such as shellfish and seaweed. As these organisms grow, they take up nutrients from the surrounding waters, and, when harvested, the nutrients they contain are directly removed.

A workshop in Stamford, organized by LISS, was held in 2009 to learn about nutrient bioextraction technologies being used around the world and to discuss the opportunities and challenges of implementing these practices in the Sound. One of the major recommendations from the workshop was the need for a Sound-based pilot study, to get local information and assess the potential effects of nutrient bioextraction on the environment.

A multi-institutional partnership has formed over the last year to conduct this pilot study in a highly-urban environment. The location for the pilot study is in the farthest western reaches of the Sound, at the confluence of the Bronx and East rivers in New York City. The Bronx River pilot study site is currently impacted by a variety of human-derived stressors common to urban waters. The nearby Hunts Point STP releases 200-400 million gallons of treated effluent per day, combined sewer overflows are a recurring problem, and the large amount of impervious surfaces in the area exacerbates ongoing problems with polluted stormwater. The original habitat along the Bronx River was predominantly salt marshes inhabited by dense populations of ribbed mussels (Geukensia demissa). These salt marshes became degraded (and in many cases eliminated) as the city expanded along the rivers.With the loss of habitat, the capacity of the local shellfish to filter microorganisms fertilized by high nutrient levels from the ecosystem was also lost.

The Bronx River Watershed Initiative is funding the installation of a raft of ribbed mussels to evaluate the potential for shellfish aquaculture to increase biological filtration activity in this environment. The raft will be installed and maintained by Pemaquid Mussel Farms, a commercial mussel-aquaculture firm from the state of Maine, and Rocking the Boat, a local youth development organization. NOAA’s Milford Laboratory will be monitoring the raft to measure impacts of the mussels on local water quality. The Sound Futures Fund has funded researchers at UConn to install and monitor seaweed grown on longlines alongside the mussel raft. Finally, EPA’s Office of Research and Development has provided funding to model the potential impacts of shellfish aquaculture on Long Island Sound using data from the pilot study, and to provide an economic assessment of shellfish nutrient bioextraction. The modeling and economic assessment team is being led by NOAA’s Center for Coastal  Monitoring and Assessment. The pilot study is scheduled to begin in 2011 and continue for two years.

Reprinted from the 2009-2010 Long Island Sound Study  Biennial Report

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