Sub-daily variations in nitrous oxide fluxes from the littoral zone of a temperate eutrophic lake

Elucidating the variability in nitrous oxide (N₂O) emissions from inland waters is important for evaluating the global N₂O budget accurately. However, labor-intensive sampling and gas analysis have confined evaluations of temporal variability in lakes to the seasonal time scale. We used a state-of-the-art laser-based N₂O analyzer combined with a floating chamber to examine the sub-daily variations in N₂O emissions from a shallow eutrophic lake in Japan. We conducted intense daytime field campaigns during different seasons to reveal differences in these emissions in conjunction with the dynamics of dissolved N₂O concentrations in the lake water. The study revealed that N₂O fluxes varied within a day: emissions increased in response to increases in wind speed. Variations in surface dissolved N₂O concentrations caused by water mixing were also important during the summer, when under stably stratified conditions accumulation of N₂O initially occurred in the lake bottom water layer. In addition, in a shallow lake, the N₂O production/consumption balance may vary substantially within a day due to a change in dissolved oxygen concentration, which affects dissolved N₂O concentration and in turn, emissions into the atmosphere. These findings demonstrate the need to consider diurnal variability when estimating cumulative N₂O emissions accurately over long periods.