三峡水库不同运行工况下中段干流碳源气体释放通量研究

来自陆地大量有机碳源的输入,以及三峡库区调度运行和筑坝蓄水导致CO_2、CH_4等碳源气体的排放成为近来关注的热点。以三峡库区干流中段为研究对象,于2017年8月—2018年11月对忠县(ZX),万州(WZ),涪陵(FL)进行每月采样分析,探求水-气界面CO_2、CH_4通量在水库不同运行工况下的变化特征。研究发现,在观测期间内,ZX采样点CO_2浓度在0.008 6～0.115 3 mmol/L波动,WZ采样点CO_2浓度在0.003 5～0.116 8 mmol/L波动,FL采样点0.006 3～0.098 6 mmol/L,整体上3个采样点的CO_2浓度变化趋于一致,都在库区泄水期运行4—5月CO_2浓度达到峰值,在低水位运行期的6—9月降到最低值。CH_4通量在水库低水位运行期表现为"汇",FL点位在泄水期达到"源"的最大值;3个采样点的CO_2通量在泄水期均表现为"源"的特征,低水位运行期的CO_2通量表现为"源"与"汇"的转换。通过与国外已有水库监测数据比较分析,CO_2扩散通量在全球水库序列中处于中等水平,CH_4扩散通量在全球水库序列中处于中等偏下水平。

Study on the release fluxes of carbon source gases under different operating conditions in the middle reach of the main stream of the Three Gorges Reservoir

The input of large quantities of organic carbon sources from the land, and the discharge of carbon sources such as CO₂ and CH₄ caused by the operation and damming in the Three Gorges Reservoir Area have become the hot spots of recent research. In order to reveal the variation characteristics of CO₂ and CH₄ concentrations in different flow levels in the Three Gorges Reservoir Area, this study took the middle reach of the main stream of the Three Gorges Reservoir as the research objects. Samples were taken from Zhongxian County (ZX), Wanzhou (WZ), Fuling (FL)monthly from August 2017 to November 2018 to analyze and study the characteristics of CO₂ and CH₄ fluxes at the water-air interface under different operating conditions. Results showed that during the research period, CO₂concentration of the ZX, WZ and FL was between 0.008 6 mmol/L and 0.115 3 mmol/L, 0.003 5 mmol/L and 0.116 8 mmol/L, and 0.006 3 mmol/L and 0.098 6 mmol/L, respectively. The concentration of CO₂ at these three sampling points tended to be consistent and reached its peak during the drain period from April to May and its lowest point in the low water level operation period from June to September. CH₄ flux exhibited the feature of a sink during the operation at a low water level, but at FL it reached the maximum value as a source in the discharge period. The CO₂ fluxes at the three locations showed the feature of a source during the discharge period, but during low water level operation period, CO₂ flux indicated the switch between a source and a sink. CO₂ flux was at a medium level and CH₄ flux was at a lower-middle level compared with those of other reservoirs in the world.