Nitrous oxide (N₂O) is a potent climate gas, with its strong warming potential and ozone-depleting properties both focusing research on N₂O sources. While N₂O sinks have been reported in many oxic waters, these remain poorly understood and are often dismissed simply as the reduction of N₂O to N₂ through denitrification. Although a sink through biological N₂O fixation has been observed in the Pacific, the regulation of N₂O compared to canonical N₂ fixation is unknown. Here we show that both N₂O and N₂ can be fixed by freshwater communities but with distinct seasonalities and temperature dependencies. While N₂ fixation is stronger in spring and summer, N₂O fixation appears to be independent of temperature, driving a strong N₂O sink in winter. Moreover, by quantifying both N₂O and N₂ fixation we show that N₂O fixation is direct, rather than N₂O being first reduced to N₂ through denitrification, and direct N₂O fixation may explain N₂O sinks widely reported in natural waters. With weaker N₂O sinks at higher temperatures, rising temperatures could result in an erosion of the natural sinks for N₂O.

Primary Presenter: Yueyue Si, Queen Mary University of London (yueyuesi00@gmail.com)

Authors:

Yueyue Si, Queen Mary University of London  (yueyuesi00@gmail.com)

Yizhu Zhu, Queen Mary University of London  (yizhu.zhu@qmul.ac.uk)

Ian Sanders, Queen Mary University of London  (i.a.sanders@qmul.ac.uk)

Dorothee Kinkel, Queen Mary University of London  (d.b.kinkel@qmul.ac.uk)

Kevin Purdy, University of Warwick  (K.Purdy@warwick.ac.uk)

Mark Trimmer, Queen Mary University of London  (m.trimmer@qmul.ac.uk)