Shellfish aquaculture is an established industry on Cape Cod. It employs many producers, and yields a valuable end product. Applying shellfish aquaculture to nitrogen management is a non-traditional approach for improving water quality in estuaries. Oysters have been selected for the Demonstration Project because they remove significant amounts of nitrogen due to their relatively fast growth over other endemic shellfish. In addition, culture techniques are well known and oysters have a high market value. Oysters are highly efficient filter feeders, consuming the plankton which grows on dissolved nitrogen and other nutrients in the water.
The plankton proliferates excessively because of the high nutrient inflows to the pond. These algae then die and decompose, releasing more nutrients such as hydrogen sulfide that causes odors and can lead, in some instances, to fish kills. In addition, the algal blooms increase the biological oxygen demand in the estuaries that can approach nearly anoxic conditions. This also stresses the fish and other aerobic organisms living in the water. By feeding, oysters manage the concentration of plankton that continues to regenerate and grow on dissolved nutrients. In this way, oysters improve water quality. It has also been shown that shellfish waste products may augment denitrification of bottom sediments, thereby releasing nitrogen in the form of nitrogen gas to the atmosphere, 78% of which is already nitrogen gas.
Working through the WQMC and the Department of Marine and Environmental Services, the town has achieved a number of milestones and has launched the full-scale implementation of the Demonstration Project. The goal is to establish and quantify the causal relationship between shellfish cultivation and improved water quality.