Subdaily 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 to accurately evaluate the global N2O budget. 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 subdaily 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 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 because of a change in dissolved oxygen concentration, which affects dissolved N2O concentration and, in turn, atmospheric emissions. These findings demonstrate the need to consider diurnal variability to accurately estimate cumulative N2O emissions over long periods.