Water quality upstream and downstream of a commercial oyster aquaculture facility in Chesapeake Bay, USA

Oyster aquaculture is an expanding industry in the Chesapeake Bay. Oysters remove nitrogen (N) and phosphorus (P) from the water column through filtration and conversion of phytoplankton into shell and tissue, but also continuously excrete these same nutrients back into the water column as inorganic compounds readily available for plant or algal uptake. The objective of this study was to assess multiple water quality parameters upstream and downstream of a commercial oyster aquaculture facility in the mesohaline region of the Chesapeake Bay. Results of the study indicated a 78.4% average increase in total ammonia nitrogen (TAN) concentration and a 19.4% decrease in chlorophyll-a (Chl-a) concentration downstream of the facility. There was no significant change in the concentration of reactive phosphate (RP), nitrate-nitrogen (NO3−-N), or nitrite-nitrogen (NO2−-N) as water passed through the facility. It was determined that velocity of water through the facility had no influence on the change in TAN or Chl-a concentration from upstream to downstream of the facility. Increased reduction in Chl-a concentration from upstream to downstream was related to higher upstream concentrations of Chl-a. There was no correlation between increased rates of Chl-a removal and downstream TAN. Results of this study suggest that oyster aquaculture can significantly increase the amount of available inorganic nitrogen in the water column immediately downstream of a facility, independent of upstream availability of phytoplankton and flow velocity of water through the facility.