A model of oxygen reduction, denitrification, and organic matter mineralization in marine sediments1

Porewater nutrient profiles are sensitive indicators of organic matter degradation in sediments. To interpret these data, we have derived a kinetic model of oxygen reduction, nitrification, and denitrification which quantitatively relates the rates of oxygen reduction and denitrification to the depth separating these processes and the carbon oxidation rate. We have compared model profiles with porewater profiles of the sum of NO2−, NO3−, and NH4+ (∑N) from both Atlantic and Pacific Ocean stations. Calculated rates of oxygen reduction and denitrification vary proportionally at these stations. Extrapolation along this relationship predicts a maximum in NO3− even where the nitrification zone is so thin that only a decrease from bottom water samples is measured with a 1–2-cm sampling interval. The model also predicts that the maximum amount of organic matter that can be oxidized by denitrification is only 30% of that oxidized by oxygen respiration in the Pacific and only 13% in the Atlantic Ocean.