OXYGEN REGULATION OF NITRIFICATION AND DENITRIFICATION IN SEDIMENTS

Oxygen regulation of nitrification and denitrification in sediments wa s investigated with N-15-isotope techniques. Sediment cores were incub ated in a continuous flowthrough system in which the O-2 concentration was varied in the overlying water while the NO3- concentration was ke pt constant. Nitrification was stimulated with increasing O-2 concentr ations in the overlying water from 0 to 100% of atmospheric saturation , whereas only a slight stimulation was observed above 100%. At O-2 co ncentrations below 100% of atmospheric saturation, NO3- from the overl ying water was the most important source of N for denitrification, whe reas above 100% of atmospheric saturation, NO3- produced by nitrificat ion 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 th e diffusional distance of NO3- to the anoxic zone of denitrification a nd consequently the location of NO3- vertically in the sediment as wel l 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 co ntaining high NO3- concentrations (such as eutrophic lakes and streams ).