Short-term field observations of nitrous oxide saturations in Lake Taihu, China: the need for high temporal resolution studies

The incomplete understanding of the processes which control aquatic nitrous oxide (N2O) production is partially due to a lack of onsite data with which to describe the temporal resolution of N2O production. To help resolve this, we directly measured the N2O saturation (relative to atmospheric partial pressure) on an hourly basis over two survey periods (July and September 2003) in Lake Taihu, a large eutrophic lake in eastern China. July N2O saturations displayed a distinct diurnal pattern, opposite to those observed by others in subtropical streams, but similar to N2O emissions observed from incubated estuarine sediments. Correlative analyses indicate that biogeochemical processes operate as important controls on N2O production over very short time scales. Nitrous oxide production processes are not only regulated by O2 dynamics related to microalgal photosynthesis, but also closely related to organic matter decay at the sediment-water interface. While large-scale changes (approximately 25-fold) in N2O fluxes in Lake Taihu are a function of variable N loading, biogeochemical processes concerning O2 and N transformation at the sediment-water interface have significant (-twofold) impacts on the regulation of N2O production over very short time scales. Further, high temporal resolution research focused on developing a comprehensive understanding of lacustrine N2O production, including natural and anthropogenic loading and biogeochemical transformation processes, is clearly needed.