Effect of oxygen concentration on denitrification in freshwater sediment

The effect of different O 2 concentrations on denitrification in freshwater sediment was studied using the acetylene blockage technique. Denitrification occurred over a wide range of O 2 concentrations ranging from 10.1 to 0.33 μmol ml −1 in nitrate amended sediment. However, denitrifying activity was not observed in sediment incubated under similar conditions when NO 3 ‐was absent. These observations suggested that an anoxic environment or low O 2 concentrations were not required for denitrification to occur, if NO 3 ‐ was initially present in the sediment. Denitrification gradually decreased as the dissolved O 2 concentration in sediment increased to 0.25 μmol ml −1 . However, between 0.25 and 0.35 μmol ml −1 dissolved O 2 , denitrifying activity was higher than at the lower dissolved O 2 concentration (0.25 μmol ml −1 ).