Eutrophication and the rate of denitrification and N20 production in coastal marine sediments

Large (13 m3, 5 m deep) microcosms with coupled pelagic and benthic components were used to measure the effect of nutrient loading and eutrophication in coastal marine ecosystems on the rates of benthic denitrification (N2) and N2O production. After 3 months of daily nutrient addition, average denitrification rates ranged from about 300 µmol N m−2 h−1 in the sediments of the control microcosm to 880 in the most enriched microcosm. which received 65 times the nutrient input of the control. Increases in the production of N2O were more dramatic and increased by a factor of about 100, from 0.56 µmol N m−2 h−1 in the control to 51 in the most enriched microcosm. Although there was a clear increase in the denitrification rate in the more eutrophic systems, the amount of fixed nitrogen removed was a constant or progressively smaller fraction of the nitrogen input. Even in the most enriched microcosm, at least 16% of the N input was removed by denitrification.