Spatiotemporal distribution of nitrous oxide (N2O) emissions from cascade reservoirs inLancang-MekongRiver Yunnan section, Southwestern China

The current issue of river damming causing the release of greenhouse gas nitrous oxide (N2O) from reservoirs has led to a debate over whether hydropower can still provide clean energy. In January (dry season) and August 2019 (wet season), we detected the N2O concentrations from cascade reservoirs in Lancang-Mekong River Yunnan section by using static headspace gas chromatography and estimated the emission flux by the boundary layer approach to explore the influencing factors, especially the impact of cascade reservoirs development and operation. In the Lancang River (Yunnan section), the longitudinal distribution of N2O concentration along the cascade reservoirs showed seasonal differences. The average concentrations of N2O during the dry season and the wet season were 13.50 +/- 2.00 nmol/L and 16.40 +/- 4.10 nmol/L, respectively. The reservoirs with thermal stratification in both seasons were the Xiaowan (XW), Nuozhadu (NZD), and Jinghong (JH) reservoirs. The vertical distribution of N2O concentration was depth dependent (i.e., the deeper the location, the higher the concentration) in reservoirs with thermal stratification and uniform in reservoirs without thermal stratification. Dissolved oxygen (DO), water temperature, and other biogenic elements were the main factors affecting N2O distribution. The average N2O emission flux in the cascade reservoirs was 12.80 +/- 2.60 mu mol m(2)center dot day(-1)during the dry season and 16.10 +/- 4.75 mu mol m(2)center dot day(-1)during the wet season. The annual average N2O emission fluxes of all reservoirs were in an order of JH > XW > Dachaoshan (DCS) > NZD > Miaowei (MW) > Gongguoqiao (GGQ) > Manwan (Man W). In 2019, a total of 3.37 x 10(6) mol year(-1)(94.39 ton N2O-N year(-1)) was released from the water surface of the cascade reservoirs, which accounted for approximately 0.31% of the total N2O emissions from reservoirs worldwide. This study shows the cascade reservoirs development and operations have made the Lancang River (Yunnan section) a major area for N2O emissions.

Automated summary

The study on cascade reservoirs in the Lancang River (Yunnan section) reveals that the development and operation of these reservoirs have made it a significant area for N2O emissions, with concentrations varying by season and influenced by factors such as water temperature and dissolved oxygen levels.