低气压对高海拔湖泊甲烷气泡排放的驱动力及机理

Due to its critical control on methane ebullition from lakes, the atmospheric pressure is thought to be the "trigger" of methane flux. However, our kownledge about the relationship between methane ebullition and atmospheric presure is limited in low altitute regions, and in temporal variation. The potential effect of low atmospheric pressure in high altitute environment on the methane ebullition from countless lakes in alpine regions worldwide, are urgently needed to be monitored..In the present program, two lakes, one in middle altitute (2150 m a.s.l.)and one in high altitute (3450 m a.s.l.), will be choosen to be studied. Sediment cores selected from each lake will be taken back to lab and placed into PVC tubes，with manipulated capsules of air pressure fixed to two air pressure gradient corresponding to the two altitutes, respectively. Under those condition, methane production, methane bubbles formation, transport in sediment and their emission to atmosphere will be studied, while in situ methane daynamics in lakes will be studied as well. Based on the results of those experiment, we aim to analysis the effect of low atmospheric pressure in high altitute environment on methane ebullition from lakes in alpine region, and confirm the key proccess that atmospheric pressure controlled. This program would be halpful to filling the kownledge gap of methane daynamics in alpine lakes, and quantifying the source strength of methane emission from lakes in global scale.

甲烷是大气中重要的温室气体。湖泊是甲烷排放的"热点"，其排放的甲烷绝大部分通过气泡途径进入大气。低海拔地区大气压力在时间尺度上小幅下降即能极大提高湖泊甲烷气泡排放速率。高海拔地区通常是湖泊分布的集中区域，但目前大气压力在海拔梯度上的大幅下降对高海拔湖泊甲烷气泡排放的影响尚不明确，这在很大程度上增加了全球甲烷源强的不确定性。.本项目选取位于中、高两个海拔梯度的湖泊各一个作为研究对象。采用人为模拟的方法对取自同一湖泊的沉积物分别施加两个海拔梯度所对应气压值的控制试验，以对沉积物甲烷排放的相关过程进行动态监测与分析。同时，在野外监测湖泊原位状态下的甲烷排放过程。通过综合分析上述实验的结果，探讨大气压力在海拔梯度上的变化对湖泊甲烷气泡排放途径的影响，从而进一步揭示大气压力控制甲烷气泡排放的关键过程及其机理，最终为解析高海拔湖泊的甲烷动态和准确估算全球湖泊的甲烷源强提供基础数据和理论依据。

项目在位于喜马拉山脉南坡的尼泊尔境内分别选择了位于中（海拔2000m）、低（海拔286m）海拔的两处样点，作为本项目的野外监测样点，替代原本计划的两个样点。基于观测到的数据，对两处湿地甲烷排放的日动态和季节动态进行了系统分析，是针对喜马拉雅南坡地区湿地温室气体排放的首次实验性报道，填补了这一地区湿地温室气体排放的数据空白，对未来区域性温室气体评估具有较高的参考价值。在高海拔低气压控制甲烷气泡排放的机理方面，项目基于前期已有的在高海拔湖泊（若尔盖花湖）甲烷排放方面的工作基础和积累的数据，找到了低气压控制高海拔湖泊甲烷气泡排放的佐证，弥补了控制实验缺失对本项目的影响。该部分研究不仅是青藏高原湖泊湖面甲烷排放的首例实验性报道，更为重要的是，低气压作为高原湖泊甲烷排放重要驱动力的观点系首次被提出，这一结论暗示了今后对包括青藏高原在内的高海拔地区湖泊的甲烷排放评估时应引起重视。

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