三峡水库上空甲烷浓度时空变化及与水库甲烷通量的关系

SPATIAL AND TEMPORAL VARIATION OF METHANE CONCENTRATIONS IN THE ATMOSPHERE OF THE THREE GORGES RESERVOIR AND ITS RELATIONSHIP WITH METHANE EMISSIONS FROM THE RESERVOIR

2010年,对三峡水库水-气界面上空0.5m处和岸边甲烷的浓度进行全年的观测,并采用静态浮箱-气相色谱法测定水库水-气界面上的甲烷通量,研究了三峡水库上空的甲烷浓度的背景值及其与甲烷排放强度之间的关系。结果表明:三峡水库上空甲烷浓度的年平均值为2.216±0.224mL/m3,岸边甲烷浓度的年平均值为2.211±0.206mL/m3,两者差异不显著;除夏季时云阳上空的甲烷浓度较高外(2.850mL/m3),其余地点上空的甲烷浓度都接近年平均值;三峡水库上空的甲烷浓度存在明显的空间差异,上游地区(云阳)上空的甲烷浓度(2.31±0.33mL/m3)显著高于下游地区(秭归:2.14±0.13mL/m3,巫山:2.20±0.18mL/m3),坝后河流(三斗坪:2.21±0.16mL/m3)上空的甲烷浓度高于坝前秭归处,但差异不显著。这一格局与水库中甲烷通量的空间变异基本相同,即从上游到下游(云阳、巫山、秭归)江面上甲烷通量依次为0.454,0.260和0.115mg/(m2.h),呈下降趋势,坝后三斗坪处的甲烷通量(0.280mg/(m2.h))显著高于坝前秭归处通量,这表明:水库的水-气界面上的甲烷排放强度是影响水库上空甲烷浓度变化的主要因素。

The background value of methane（CH4） concentration was measured in 2010 at 0.5 m above the water-atmosphere interface and the bank of the Three Gorges Reservoir（TGR）.CH4 fluxes from the TGR were determined by the static floating chamber and gas chromatography analysis methods.The results showed that the annual average of CH4 concentration was 2.216±0.224 mL/m3 at 0.5m above the water-atmosphere interface and 2.211±0.206 mL/m3 at the bank of the TGR,and the difference between them was not significant.Seasonal variations of CH4 concentrations were very small.CH4 concentrations were up to 2.850 mL/m3 at the water-atmosphere interface of Yunyang in summer.But in the other sites,seasonal average CH4 concentrations varied small and were close to the annual average value.There were apparently spatial variations in CH4 concentration at 0.5 m above the reservoir surface.The CH4 concentration gradually decreased from Yunyang（2.31±0.33 mL/m3）,Wushan（2.20±0.18 mL/m3） to Zigui（2.14±0.13 mL/m3） with the distance from the Three Gorges Dam（TGD）.Furthermore,the CH4 concentration in the river downstream of the TGD（Sandouping：2.21±0.16 mL/m3） was higher than that in the upstream of the TGD（Zigui：2.14±0.13 mL/m3）,but there was no significant difference between the two sites.The annual average CH4 fluxes of three sites from the upstream to the downstream in the TGR were 0.454,0.260 and 0.115 mg/（m2·h）,respectively,and the average CH4 flux in the downstream dam site（Sandouping） was also higher than that in the upstream dam site（Zigui）.The spatial pattern of CH4 concentrations in the TGR was the similar with that of CH4 emission fluxes,which showed that CH4 fluxes were a crucial factor causing the difference of the CH4 concentrations in the TGR.