Nitrous oxide (N2O) is an important greenhouse gas and has a great impact on global warming. Affected by human activities, rivers, and reservoirs have become active sites for N2O production and emission. In Three Gorges Reservoir and the downstream Yangtze River, the concentrations and fluxes of dissolved N2O were investigated in September-October 2009 and October 2016 to identify the factors controlling the distribution of N2O in the reservoir and the effect of damming and reservoir operation on N2O emission from the Yangtze River. The dissolved N2O concentration of the reservoir ranged from 9.74 to 16.36 nmol·L-1 with an average of (12.49±1.75) nmol·L-1 in the surface water (about 0 m) and ranged from 9.99 to 14.00 nmol·L-1 with an average of (11.21±0.91) nmol·L-1 in the bottom water (ranging from 6 m to 103 m). The dissolved N2O in the water column of Three Gorges Reservoir varied little, and no significant difference was noted between the overall N2O concentration in the reservoir and that in the downstream river. A positive correlation was noted between N2O and nitrate (NO3-) (P<0.01), although negative correlations were found between N2O and ammonium (NH4+) (P<0.05) and nitrite (NO2-) (P<0.01) in Three Gorges Reservoir. The surface N2O in the Three Gorges Reservoir was overall saturated, with saturation ranging from 122% to 170% in 2009 and from 114% to 187% in 2016. The mean emission rate of N2O from the surface water was (4.6±2.4) μmol·(m2·d)-1 in 2016 and (16.6±4.9) μmol·(m2·d)-1 in October 2009. The Three Gorges Reservoir is a non-negligible source of atmospheric N2O. No obvious difference was noted between upstream and downstream N2O concentrations, which implies that no degassing emission occurs when water passes through turbines and spillways.
Keywords: Three Gorges Reservoir; Yangtze River; damming; emission; nitrous oxide.