Nitrous oxide (N₂O) emissions from the high dam reservoir in longitudinal range-gorge regions on the Lancang-Mekong River, southwest China

Nitrous oxide (N₂O) is a greenhouse gas that should not be overlooked, and its emissions from plain reservoirs as well as small- and medium-sized reservoirs have been extensively studied; however, N₂O emission patterns from high-dam reservoirs in longitudinal range-gorge regions remain unclear. In this study, the N₂O concentration and emission flux from the high-dam Xiaowan Reservoir were investigated using static headspace gas chromatography and a boundary layer approach in the Lancang River. The factors influencing N₂O production and emissions, especially the influence of damming, were explored. Our results demonstrated that the Xiaowan Reservoir, a source of N₂O emissions, had an N₂O emission flux of 15.48 ± 2.87 μmol m²·d^-1 in 2019; the N₂O concentration and emission flux exhibited an increasing trend along the flow direction within the Xiaowan Reservoir but decreased downstream of the dam. During the two water seasons, water temperature, the concentration of DO, NO₃^- and NH₄⁺are all influencing factors of the N₂O concentration in the XWR. the N₂O in the XWR during the wet season was produced by nitrification, during the dry season the production mechanism of N₂O was relatively complicated, but mainly produced by nitrification. This study advances our knowledge of N₂O emissions from high-dam reservoirs in longitudinal range-gorge regions.