[Spatial and Temporal Variability of CO Emissions from the Xin'anjiang Reservoir].

Xin'anjiang Reservoir is the largest reservoir in eastern China, with a surface area of 580 km and a mean depth of 30 m. It is in an oligotrophic or mesotrophic state at present. This study measured carbon dioxide (CO) emissions from the upstream river, the reservoir's main body, and the river downstream of the Xin'anjiang Reservoir to investigate the spatial and seasonal variability of CO emissions from the water surface using static floating chambers and gas chromatography. Results showed that the downstream river had, significantly, the highest CO emission flux[(1535.00±1447.46) mg·(m·h)], followed by the upstream river[(120.39±135.41) mg·(m·h)]. The reservoir's main body had the lowest flux[(36.65-61.94) mg·(m·h)]. The high CO emission flux in the downstream river was probably influenced by turbulence during the discharge periods, which would allow the dissolved CO in the hypolimnion before the dam to be released to the atmosphere in the watercourse of the downstream river. However, the CO emission flux decreased with distance to the dam, likely because of the drop in strength of the turbulence. Moreover, there was an obvious alternation between CO source and CO sink in the main body of the reservoir, with CO sources in autumn and winter and CO sinks in spring and summer. The maximum and minimum CO emission values occurred in winter and spring, respectively. Such variability in the CO emissions was probably influenced by the bloom of alga in spring and summer, because dissolved CO in the water was absorbed by the respiration of alga. However, hydrologic conditions were unstable in the upstream river due to a fast water flow, so alga was difficult to bloom there, and a CO source was observed throughout the year, except during April and August. The measurement of the flux from the upstream river, main body, and downstream river required a long period for the investigation of greenhouse gas emissions to avoid underestimating the total CO emission from a hydroelectric reservoir system.