Yang Le, Li He-Peng, Sun Bin-Feng, Yue Chun-Lei
Zhejiang Academy of Forestry, Hangzhou 310023, China.
Agricultural Engineering Research Institute of Jiangxi Academy of Agricultural Sciences, Nanchang 330200, China.
Huan Jing Ke Xue. 2017 Dec 8;38(12):5012-5019. doi: 10.13227/j.hjkx.201704190.
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.
新安江水库是中国东部最大的水库，水面面积580平方千米，平均深度30米。目前处于贫营养或中营养状态。本研究通过静态浮箱和气相色谱法测量了新安江水库上游河流、水库主体及下游河流的二氧化碳（CO₂）排放，以研究水面CO₂排放的空间和季节变化。结果表明，下游河流的CO₂排放通量最高[（1535.00±1447.46）毫克·（平方米·小时）]，其次是上游河流[（120.39±135.41）毫克·（平方米·小时）]。水库主体的通量最低[（36.65 - 61.94）毫克·（平方米·小时）]。下游河流较高的CO₂排放通量可能受泄流期湍流影响，使大坝前下层滞水层中溶解的CO₂在下游河道水流中释放到大气中。然而，CO₂排放通量随距大坝距离增加而降低，可能是由于湍流强度减弱。此外，水库主体存在明显的CO₂源和CO₂汇交替现象，秋冬为CO₂源，春夏为CO₂汇。CO₂排放的最大值和最小值分别出现在冬季和春季。这种CO₂排放的变化可能受春夏藻类大量繁殖影响，因为水中溶解的CO₂被藻类呼吸吸收。然而，上游河流因水流湍急，水文条件不稳定，藻类难以大量繁殖，除4月和8月外，全年均观测到CO₂源。测量上游河流、主体和下游河流的通量需要较长时间来调查温室气体排放，以避免低估水电水库系统的总CO₂排放量。
