Nitrous oxide (N₂O) is the main stratospheric ozone depleting agent, and one of the strongest greenhouse gases, about 300 times more potent than carbon dioxide. Ammonia oxidizers and denitrifiers are microbial groups that are supposed to control the N₂O budget in aquatic systems. However, recent studies suggest that abiotic reactions such as chemodenitrification may also contribute to the N₂O production. Here, we describe a novel process contributing to the production of N₂O, which we refer to as photochemodenitrification. We detected a significant and consistent production of N₂O induced by sunlight under abiotic conditions. This production varied from 3.3 to 317.4 nmol m^-2 d^-1 (i.e., from 0.4 to 31.0 nmol L^-1 d^-1) in two freshwater reservoirs in different years. Using ¹⁵N-labelled tracers, we demonstrated that nitrite and nitrate acted as substrates for this process in a freshwater reservoir and a coastal area. Unexpectedly, the N₂O production by photochemodenitrification exceeded the biological production of N₂O by ammonia oxidation in surface waters in the study reservoirs and may explain the higher N₂O emissions detected at daytime in these reservoirs. Our results demonstrate that photochemodenitrification may be an essential and overlooked process occurring in both, fresh and marine waters, globally, and responsible for a significant fraction of the N₂O emission of aquatic systems.

Primary Presenter: Elizabeth Leon Palmero, Princeton University & University of Southern Denmark (ell@sdu.dk)

Authors:

Elizabeth Leon-Palmero, Department of Geosciences, Princeton University  (el23@princeton.edu)

Rafael Morales-Baquero, Department of Ecology, University of Granada  (rmorales@ugr.es)

Bo Thamdrup, Department of Biology, University of Southern Denmark  (bot@biology.sdu.dk)

Carolin Löscher, Department of Biology, University of Southern Denmark  (cloescher@biology.sdu.dk)

Isabel Reche, Department of Ecology, University of Granada  (ireche@ugr.es)