Denitrification and Nitrous Oxide Production in a Coastal Marine Ecosystem

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 $115 \mumol N\cdot m^-2 \cdot h^-1$, with lowest values at $2^\circ C$ in winter and highest at $15^\circ C$ 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 dentrification. 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