NITROGEN GAS FLUX FROM SEDIMENTS - INSIGHTS FROM SIMULATION MODELING

Direct measurements of dinitrogen efflux from continental shelf sedime nts indicated that denitrification (mean 3.2 mmol N m(-2) d(-1)) was v ery important in nitrogen cycling. Most dinitrogen came from sediment- nitrate, AU ammonium produced in these sediments was probably nitrifie d and then denitrified. In a closed incubation, the linear production of dinitrogen, as oxygen decreased, was unexpected as was the low rati o of oxygen consumption to denitrification (3.6:1). Simulation modelli ng suggests the following explanation: Most carbon is oxidised anoxica lly, but nitrogen (ammonium) diffuses to the oxygen zone relatively de ep in the sediment, where high rates of coupled nitrification-denitrif ication result. As oxygen decreases, the zones of nitrification and de nitrification move upward. The nitrate initially present in the enclos ed overlying water decreases, but due to the decreasing diffusional pa th to the zone of denitrification, its rate of denitrification remains constant. The concentration of nitrate from sediment nitrification in creases in the overlying water, but due to the decreasing rats of sedi ment nitrification, its rate of denitrification is also constant.