OXYGEN REGULATION OF NITRIFICATION AND DENITRIFICATION IN SEDIMENTS

Oxygen regulation of nitrification and denitrification in sediments was investigated with N-15-isotope techniques. Sediment cores were incubated in a continuous flowthrough system in which the O-2 concentration was varied in the overlying water while the NO3- concentration was kept constant. Nitrification was stimulated with increasing O-2 concentrations in the overlying water from 0 to 100% of atmospheric saturation, whereas only a slight stimulation was observed above 100%. At O-2 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 O-2 levels on the source of NO3- can be explained by applying a simple one-dimensional model: O-2 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 O-2 conditions will stimulate denitrification, while the opposite will occur in systems containing high NO3- concentrations (such as eutrophic lakes and streams).