An Analysis of Denitrification and Anammox Processes in Sediments Underneath Oyster Aquaculture

Oysters play a very important role in the removal of nitrogen from eutrophic waters. While the amount of nitrogen that is converted into biomass is well studied, little is known about the additional amount of nitrogen that may be removed from the sediments due to the presence of oysters. The purpose of this project was to examine microbial processes that occur in sediments under oyster aquaculture cages in local ponds/estuaries, and to measure the rates of key processes associated with nitrogen removal. Little Pond and West Falmouth (Cape Cod, Massachusetts) are coastal waterways that are degraded due to nitrogen loading. Oyster aquaculture operations have been installed at both sites to help clean up those eutrophic estuaries. We measured nitrate and ammonia concentrations in porewaters and water columns. Direct measurements of rates of denitrification and anaerobic ammonium oxidation (anammox) were completed with Membrane Inlet Mass Spectroscopy (MIMS). Genes and transcripts associated with denitrification and anammox in sediments under oysters and at control sites were calculated using quantitative PCR. Results suggest that rates of denitrification are 2-30 times higher under oysters than at control sites, and gene expression patterns provide a second line of support for those findings. The ultimate goal of the project is to provide data to improve models of the nitrogen removal potential of shellfish aquaculture as a possible remediation strategy for improving the quality of eutrophic coastal waters.