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 remove nutrients from the Patuxent River estuary. Using models, field data, and input from stakeholders, we are evaluating aquaculture success, water quality improvement, economic benefits, and the potential credit for 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 the 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. We are studying the nutrient removal potential of cultivated and harvested shellfish—focusing on the eastern oyster and the northern quahog—and estimating the value of the ecosystem functions and services maintained or enhanced via aquaculture. We are also evaluating the potential costs and applicability of shellfish aquaculture as a nutrient management measure.
We are using two models, the Assessment of Estuarine Trophic Status (ASSETS) model to determine the eutrophication status and the Farm Aquaculture Resource Management (FARM) model to determine the amount of nitrogen removed, the potential economic benefit of the water cleaning service provided by the shellfish, and the credit potential for trading nitrogen in a nutrient trading program. The FARM model also determines changes in chlorophyll and dissolved oxygen related to aquaculture that can be used to evaluate the impact of the farm on local eutrophication status.
Benefits of Our Work
The removal of phytoplankton, detritus, and particulate material through filtration by oysters, and the subsequent increase in water clarity allows seagrasses, and thus fish habitat, to reestablish in high turbidity systems. Nutrients are essentially removed from the system by sequestration into tissue and shell. If included in a nutrient trading program, a grower could receive credit and payment for the avoided cost of additional water treatment by traditional measures. This project will support development of local Chesapeake Bay nutrient water quality trading programs and water quality management programs and will provide an approach for broader application nationally. Additionally, it could stimulate seafood production and create jobs through the expansion of aquaculture activities.
We anticipate that the approach used in this study will confirm the approach that has also been used to investigate the potential benefits of shellfish aquaculture in the Potomac River estuary, Long Island Sound, Great Bay Piscataqua region estuaries, and Puget Sound, and that it will prove useful for informing nutrient management and nutrient trading in other coastal waterbodies in the U.S. and elsewhere that can support aquaculture.