Eutrophication is the overabundance of nutrients in a body of water that results in harmful algal blooms, fish kills, and in some cases ecosystem collapse. We are investigating the feasibility of using shellfish to filter out excessive nutrients in the Piscataqua estuary. Using models, field data, and input from stakeholders, we are evaluating aquaculture success, water-quality improvement, economic benefits, and the potential credit for carbon and nitrogen trading as a management strategy.
Why We Care
Eutrophication is among the most serious threats to the function and services supported by coastal ecosystems. Attempts to reverse coastal eutrophication have centered on reducing land-based sources of nutrients, such as fertilizer applications and wastewater treatment plant discharges. However, recent studies have shown that in-the-water removal of nutrients through filtration and growth of shellfish can complement land-based management methods, provide much-needed shellfish products (the United States presently imports more than 90 percent of seafood consumed), and create additional jobs and income for aquaculture farmers.
What We Are Doing
Bivalve shellfish planted in aquaculture farms improve water quality by filtering out nutrients, suspended sediment, and chlorophyll. With support from the EPA Regional Ecosystem Services Program, we are studying the nutrient removal potential of cultivated and harvested shellfish, focusing on the eastern oyster and the northern quahog. We are also estimating the value of the ecosystem functions and services maintained or enhanced via aquaculture.
The potential costs, ecosystem service benefits, and broader applicability of innovative management strategies, such as the use of shellfish aquaculture as a nutrient management measure, are being evaluated in the specific context of two regional ecosystem restoration programs: Long Island Sound (Connecticut and New York) and the Great Bay/Piscataqua region (New Hampshire and southern Maine). The two locations differ in nutrient loading, water circulation, and susceptibility to eutrophication but are both areas of active ecosystem restoration efforts.
We are using four models: System Wide Eutrophication Management (SWEM) model, Farm Aquaculture Resource Management (FARM) model, Assessment of Estuarine Trophic Status (ASSETS) model, and an economic model called INPLAN. We are evaluating the success of aquaculture (growth of shellfish), the impact of the farm on water quality (changes in chlorophyll and dissolved oxygen related to aquaculture activity), the potential economic benefit of the water cleaning service provided by the shellfish, and the credit potential for trading carbon and nitrogen in a water quality trading program.
Benefits of Our Work
The removal of phytoplankton and detritus/particulate material through filtration by oysters and clams, and the subsequent increase in water clarity allows seagrasses, and thus fish habitat, to re-establish in high-turbidity systems. Nutrients are essentially removed from the system when the shellfish are harvested. A farmer can receive credit for the avoided cost of additional water treatment by traditional measures. This project will both support regional nutrient water-quality management programs and provide tools for broader application nationally. Additionally, it could stimulate seafood production and create jobs through the expansion of aquaculture activities.
We are hoping that the approach used in this study may be used to investigate the potential benefits of shellfish aquaculture in other coastal waterbodies that can potentially support aquaculture.