Oxygen regulation of nitrification and denitrification in sediments

Abstract

Oxygen regulation of nitrification and denitrification in sediments was investigated with 15 N isotope techniques. Sediment cores were incubated in a continuous ftowthrough system in which the O 2 concentration was varied in the overlying water while the NO 3 − 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, NO 3 − from the overlying water was the most important source of N for denitrification, whereas above 100% of atmospheric saturation, NO 3 − produced by nitrification was the main source of N for denitrification. The converse effects of the O 2 levels on the source of NO 3 − can be explained by applying a simple one‐dimensional model: O 2 in the overlying water controls the diffusional distance of NO 3 − to the anoxic zone of denitrification and consequently the location of NO 3 − vertically in the sediment as well as the magnitude of the nitrification activity. Our results suggest that in aquatic environments containing low NO 3 − 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 NO 3 − concentrations (such as eutrophic lakes and streams).