Evaluating Whether Oyster Aquaculture Can Help Restore Water Quality - NERRS/NSC(NERRS Science Collaborative)

The project team established an experiment that mimicked commercial aquaculture practices and allowed for a robust comparison of nitrogen removal rates from three commonly used gear types: floating bags of oysters, oyster condos suspended in midwater, and bottom cages of oysters. All gear was deployed in the same environmental setting (Waquoit Bay, Falmouth, MA) and maintained by the Town of Falmouth in a manner that a typical grower would follow. The growing systems were maintained for two full growing seasons (2018 and 2019) and compared to a nearby control site. Every two weeks during the growing season, the team conducted a series of measurements to provide a robust estimate of nitrogen fluxes and microbial activity below each of the aquaculture operations. Measurements included: (1) nutrient analyses of sediment, porewater and bottom water samples, (2) genetic sequencing of RNA and DNA extracted from sediment samples to determine the presence and activity level of certain bacteria; and 3) measurements of N2 fluxes from sediment cores placed in flux chambers to measure N2 production rates. All three oyster growing methods enhanced nitrogen removal relative to the control site. However, gene expression data indicate that nitrogen retention may be induced under some gear, particularly after the end of July under bottom cages, and to a lesser extent other gear types.