Nitrous oxide production from nitrification and denitrification in marine sediment at low oxygen concentrations

Abstract

Measurements of N 2 O production (release of free N 2 O), nitrification, and denitrification were made simultaneously in NH 4 Cl- and KNO 3 -amended suspensions of marine sediment. An open flow system was designed for the application of low partial pressures of O 2 (0–10 kPa) to the sediment. The overall rate of N 2 O production increased dramatically at the lowest O 2 tensions (0–0.2 kPa) and had a maximum at complete anoxia. The specific rates of N 2 O production from nitrification (N 2 O n ) and from denitrification (N 2 O d ) were determined after separation of the processes with inhibitors. Within the range of 0–0.2 kPa O 2 , the rate of N 2 O n production showed an apparent maximum of 0.1 kPa O 2 where the production accounted for 25% of the total activity of nitrification ([Formula: see text] oxidation). The rate of N 2 O d production, however, continued to increase as the O 2 fell to zero. The proportion of N 2 O d to the total N 2 O d plus N 2 produced from denitrification increased at the higher O 2 tensions and reached the maximum of about 50% at 5 kPa O 2 . Except for a narrow range between 0.1 and 0.2 kPa O 2 , denitrification was the main source of N 2 O at 0–10 kPa O 2 .