Study: Oyster aquaculture has small but positive impact on Bay water quality
The rapid growth of oyster aquaculture in the Chesapeake Bay has raised questions about its effects on water quality, with proponents touting benefits including reduction of water-column nutrients and increased clarity, and other stakeholders pointing to drawbacks such as enrichment of sediment nutrients and altered current patterns.
A new field study by researchers at William & Mary's Virginia Institute of Marine Science shows minimal impacts from oyster aquaculture overall, suggesting that low-density oyster farms located in well-flushed areas are unlikely to impair local water quality. Published in today’s issue of PLOS ONE, the study was authored by VIMS doctoral student Jessie Turner along with Lisa Kellogg, Grace Massey and Carl Friedrichs. Partial funding was provided by The Nature Conservancy.
“We found differences in water quality and current speed inside and outside the farms,” says Turner, “but they were minor. The differences we measured between sites and between seasons were typically an order of magnitude greater.”
The team’s findings suggest room for growth in oyster aquaculture in the Bay, as long as growers continue using low-density culture with well-spaced cages.
“Even though we detected no effects in the water column during a single tidal cycle,” Turner says, “we know oysters take up nitrogen and phosphorus through feeding and growth, and over time we would thus expect harvesting of farmed oysters to be of benefit to the bay.”
Excess input of these nutrients via fertilizers, wastewater and other sources is a main reason for impaired water quality in the Chesapeake, with their reduction and removal a key goal of bay restoration efforts.
Andy Lacatell, Virginia Chesapeake Bay director of The Nature Conservancy, says, "This important research demonstrates that, while the positive impacts on water quality may be small, just the presence of oyster aquaculture improves the health of the bay."
The VIMS team conducted the research as part of a broader aquaculture study initiated by The Nature Conservancy in several states and countries, including assessment of issues related to oyster farming in Washington and California and seaweed farming in Indonesia and Belize.
Each of these aquaculture localities has its own issues. In the Chesapeake Bay, some stakeholders are concerned about the negative impacts of oyster farms on viewsheds and sediment nitrogen budgets, while others tout the environmental benefits — one oyster can filter a bathtub of water per day, positioning oyster farms as a means to improve conditions in an estuary experiencing decades of eutrophication due to excess nutrients.