Nitrogen and oxygen availabilities control water column nitrous oxide production during seasonal anoxia in the Chesapeake Bay

Nitrous oxide (N 2 O) is a greenhouse gas and an ozone depletion agent. One of the major uncertainties in the global N 2 O budget is the contribution of the coastal region, including estuaries, which can be sites of intense N 2 O efflux. Incubation experiments with nitrogen stable isotope tracer ( 15 N) enabled the investigation of the environmental controls of N 2 O production in the water column of Chesapeake Bay, the largest estuary in North America. The highest potential rates of N 2 O production (7.5 ± 1.2 nmol-N L −1  hr −1 ) were detected during summer anoxia, during which oxidized nitrogen species (nitrate and nitrite) were absent from the water column. At the top of the anoxic layer, N 2 O production from denitrification was stimulated by addition of nitrate and nitrite. The relative contribution of nitrate and nitrite to N 2 O production was positively correlated with the ratio of nitrate to nitrite concentrations. Increased oxygen availability, up to 7 µM oxygen inhibited both N 2 O production and the reduction of nitrate to nitrite. Therefore, reducing the nitrogen input into the Chesapeake Bay has two potential impacts on the N 2 O efflux: In the short-term, N 2 O emission will be mitigated due to nitrogen deficiency. In the long-run, eutrophication will be alleviated and subsequent re-oxygenation of the bay will further inhibit N 2 O production.