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

Ji, Qixing; Frey, Claudia; Sun, Xin; Jackson, Melanie; Lee, Yea-Shine; Jayakumar, Amal; Cornwell, Jeffrey C.; Ward, Bess B.

Nitrous oxide (inline-formulaN2O) is a greenhouse gas and an ozone depletion agent. Estuaries that are subject to seasonal anoxia are generally regarded as inline-formulaN2O sources. However, insufficient understanding of the environmental controls on inline-formulaN2O production results in large uncertainty about the estuarine contribution to the global inline-formulaN2O budget. Incubation experiments with nitrogen stable isotope tracer were used to investigate the geochemical factors controlling inline-formulaN2O production from denitrification in the Chesapeake Bay, the largest estuary in North America. The highest potential rates of water column inline-formulaN2O production via denitrification (inline-formula7.5±1.2 nmol-N Linline-formula−1 hinline-formula−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, inline-formulaN2O production from denitrification was stimulated by addition of nitrate and nitrite. The relative contribution of nitrate and nitrite to inline-formulaN2O production was positively correlated with the ratio of nitrate to nitrite concentrations. Increased oxygen availability, up to 7 inline-formulaµmol Linline-formula−1 oxygen, inhibited both inline-formulaN2O production and the reduction of nitrate to nitrite. In spring, high oxygen and low abundance of denitrifying microbes resulted in undetectable inline-formulaN2O production from denitrification. Thus, decreasing the nitrogen input into the Chesapeake Bay has two potential impacts on the inline-formulaN2O production: a lower availability of nitrogen substrates may mitigate short-term inline-formulaN2O emissions during summer anoxia; and, in the long-run (timescale of years), eutrophication will be alleviated and subsequent reoxygenation of the bay will further inhibit inline-formulaN2O production.

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Ji, Qixing / Frey, Claudia / Sun, Xin / et al: Nitrogen and oxygen availabilities control water column nitrous oxide production during seasonal anoxia in the Chesapeake Bay. 2018. Copernicus Publications.

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