Nitrous Oxide Emissions from Cascade Reservoirs: Spatial Heterogeneity and Drivers

Nitrous oxide (N₂O) is one of the major greenhouse gases (GHG) in the Earth’s atmosphere. Previous research has mainly focused on N₂O emissions from single reservoirs, while the spatial variations of N₂O emissions from cascade reservoirs and the underlying influence factors have been less studied. This study measured N₂O emissions from the surface of the cascade reservoirs. We measured the content of N₂O in seven cascade reservoirs（Miaowei(MWE), Gongguoqiao(GGQ), Xiaowan(XW), Manwan (MW), Dachaoshan(DCS), Nuozhadu(NZD), Jinghong(JH) )built on the Lancang River during the wet season in 2018. The measurement found significant spatial variation of N₂O emission from the reservoirs, with the contribution of N₂O emission in two tropical reservoirs (NZD and JH) in the lower reaches of Lancang River accounting for 54.21% of the total. The overall annual N₂O flux rate (mean ± SD) was 4.76 ± 2.87 μmol/(m²·d), relatively low compared with those from other reservoirs. Furthermore, N₂O fluxes were found to be significantly correlated with water surface temperature (T) and total nitrogen in water column (N). We also found low N₂O emission rate from downstream immediately after the dam (2.6 ± 0.56 μmol/(m²·d)). Such a low N₂O flux from cascade reservoirs should be attributable to the low nitrogen (N) loading in the water body, which is the result of multiple approaches taken to maintain water quality and protect environment to decrease the input of N.