Oxygen regulation of nitrification and denitrification in sediments

Oxygen regulation of nitrification and denitrification in sediments was investigated with 15N isotope techniques. Sediment cores were incubated in a continuous ftowthrough system in which the O2 concentration was varied in the overlying water while the NO3− concentration was kept constant. Nitrification was stimulated with increasing O2 concentrations in the overlying water from 0 to 100% of atmospheric saturation, whereas only a slight stimulation was observed above 100%. At O2 concentrations below 100% of atmospheric saturation, NO3− from the overlying water was the most important source of N for denitrification, whereas above 100% of atmospheric saturation, NO3− produced by nitrification was the main source of N for denitrification. The converse effects of the O2 levels on the source of NO3− can be explained by applying a simple one‐dimensional model: O2 in the overlying water controls the diffusional distance of NO3− to the anoxic zone of denitrification and consequently the location of NO3− vertically in the sediment as well as the magnitude of the nitrification activity. Our results suggest that in aquatic environments containing low NO3− concentrations in the overlying water (such as coastal waters), higher O2 conditions will stimulate denitrification, while the opposite will occur in systems containing high NO3−concentrations (such as eutrophic lakes and streams).