Abstract. Nitrous oxide (N2O) is a greenhouse gas and an ozone
depletion agent. Estuaries that are subject to seasonal anoxia are generally
regarded as N2O sources. However, insufficient understanding of the
environmental controls on N2O production results in large uncertainty
about the estuarine contribution to the global N2O budget. Incubation
experiments with nitrogen stable isotope tracer were used to investigate the
geochemical factors controlling N2O production from denitrification in
the Chesapeake Bay, the largest estuary in North America. The highest
potential rates of water column N2O production via denitrification
(7.5±1.2 nmol-N L−1 h−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, N2O
production from denitrification was stimulated by addition of nitrate and
nitrite. The relative contribution of nitrate and nitrite to N2O
production was positively correlated with the ratio of nitrate to nitrite
concentrations. Increased oxygen availability, up to 7 µmol L−1
oxygen, inhibited both N2O production and the reduction of nitrate to
nitrite. In spring, high oxygen and low abundance of denitrifying microbes
resulted in undetectable N2O production from denitrification. Thus,
decreasing the nitrogen input into the Chesapeake Bay has two potential
impacts on the N2O production: a lower availability of nitrogen
substrates may mitigate short-term N2O 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 N2O
production.
Electron paramagnetic resonance observations on the cytochrome c-containing nitrous oxide reductase from Wolinella succinogenes
