Project: An Ecosystem Services Assessment Using Bioextraction Technologies for Removal of Nitrogen and Other Substances in Long Island Sound and the Great Bay/Piscataqua Region Estuaries
Dates: 2012 – 2015
Team: NOAA National Centers for Coastal Ocean Science and National Marine Fisheries Service, New University of Lisbon, Longline Environment, Ltd., HydroQual, Inc., Piscataqua Region Estuaries Partnership University of New Hampshire, Northern Economics, Inc., East Coast Shellfish Growers Association, EPA Atlantic Ecology Division, EPA Long Island Sound Office
Funding: EPA 2010 Regional Ecosystem Services Research Program
Project page link: https://coastalscience.noaa.gov/project/aquaculture-eutrophication-long-island-sound/
Declining water quality from excess nutrient inputs, called eutrophication, is an issue of concern in estuaries and coastal waters around the world. These nutrients act like fertilizers for marine plants in the nearshore environment. When there are too many nutrients these plants overgrow, which can cause environmental problems. These nutrients enter nearshore waters from land, typically from sources such as wastewater treatment plants, stormwater runoff in urban areas, and fertilizer runoff in suburban and rural areas. The environmental consequences of eutrophication range from low levels of oxygen in water (hypoxia) that kill fish and reduce fishery habitat, to harmful and nuisance algal blooms that can lead to loss of important seagrass habitat. Environmental management efforts to reduce excess nutrients in coastal waters primarily focus on regulation of the land-based sources of nutrients.
This research project focused on a promising in-the-water nutrient reduction measure using the cultivation and harvest of shellfish. Bivalve shellfish such as oysters, clams, and mussels, filter microscopic plants and other organic particles from the water as they eat, and use the nutrients from their food to grow. Their feeding activities reduce the amount of organic matter that reaches the seafloor, which short circuits the development of hypoxia. Feeding by bivalve shellfish also increases water clarity so that seagrasses – habitat for many marine fishery species – have more light and can regrow.
This research project showed that oyster aquaculture compared favorably to existing nutrient reduction methods, in terms of both the cost and effectiveness of nitrogen removal. Oyster aquaculture has the added benefit of providing a sustainable source of local seafood. This innovative study used a modeling approach that combined a Long Island Sound Study water quality model (SWEM) with an ecosystem-scale aquaculture model (EcoWIN) and a farm-scale aquaculture model (FARM). The models looked at current nutrient removal and value using active areas of aquaculture lease, as well as the potential increase of nutrient removal (and value) if cultivation areas were expanded. This approach enabled scientists to calculate the nitrogen removal service provided to all of Long Island Sound by Connecticut’s oyster aquaculture industry as a whole. The Assessment of Estuarine Trophic Status (ASSETS) eutrophication assessment model was then also used to determine whether additional nutrient management would be needed after taking into account nitrogen removal provided by nutrient bioextraction.
The value of this nitrogen removal service was also estimated as part of this project. An avoided costs economic analysis used known costs of established nutrient management measures (i.e. wastewater treatment, agricultural and urban stormwater remediation) to calculate the value of the nitrogen removal provided by Connecticut’s oyster industry.
The models showed that bioextractive removal of nitrogen in LIS from Connecticut’s oyster industry currently removes an equivalent of approximately 2 percent of nitrogen inputs from the entire Long Island Sound watershed. Expansion of shellfish aquaculture could lead to removal of up to 3 percent of total nitrogen inputs. This number may sound small, but the value of the estimated nitrogen removal services that the aquaculture industry is providing to Long Island Sound is estimated to be $267.4 million and could grow to $545 million if production were expanded. In addition, these values should be considered conservative estimates since they do not include nitrogen removal by clams which are also cultivated in Long Island Sound but for which no model exists to estimate their removal capabilities. These results also do not consider removal via other oyster related processes such as enhancement of denitrification; in other locations denitrification enhancement linked to shellfish aquaculture has been estimated to nearly double the nitrogen reductions.
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