Denitrification and nitrous oxide production in a coastal marine ecosystem1

Denitrification was measured directly as the flux of N 2 from sediment cores collected at various times of year at three stations in the Narragansett Bay, R.I., area. Rates of N 2 production ranged from about 10 to 115 µ mol N·m ‒2 ·h ‒1 , with lowest values at 2°C in winter and highest at 15°C in summer. Denitrification represents a major sink for fixed N in the bay; annually the N 2 production is equal to about 50% of the fixed inorganic N loading to the bay from rivers, land, and sewage. About 35% of the organic nitrogen mineralized in the sediments is removed from the ecosystem by denitrification. The percentage of organic nitrogen being mineralized in the sediments as N 2 O relative to N 2 or NO 3 ‒ + NO 2 ‒ is higher in polluted sediments than in relatively unpolluted sediments, but in all cases is < 10%.