Seasonal fluctuations in methane emissions from reservoirs: evidence from the methane metaboliccycle throughout the in situ sediment column profile.

Studying the issue of methane emissions from reservoirs, especially elucidating the mechanism of methane greenhouse gas production, revealing the seasonal flux changes of methane production, and providing scientific theories for China's low-carbon economic development strategy of optimizing energy structure and energy conservation and emission reduction. This paper combines geochemical and biological methods, with seasonal thermal stratification as the key entry point, to study the impact of methane production and oxidation processes in reservoir sediments under different thermal stratification conditions on the spatiotemporal dynamic changes of methane from the perspective of biological transformation. The ecological niche distribution of methane production/oxidation functional microorganisms in sedimentary column profiles is finely studied, revealing the ecological adaptation mechanism and production/oxidation efficiency of methane production/oxidation functional groups. Assuming that the methane dissolution in the sediment column profile of the reservoir has obvious seasonal characteristics, the seasonal thermal stratification of the Hongfeng Lake reservoir may be a key factor in the seasonal methane emission differences. The production and emission of methane from in-situ sedimentary columns may be influenced by other electron acceptors.
The distribution data of methane dissolution on sedimentary columns indicate that the methane dissolution in the in-situ sedimentary column profile of the reservoir has obvious seasonal characteristics, and the methane metabolism heat zone in summer sediments shifts upward. The results of indoor cultivation experiments further verified the distribution changes of methane heat zones in sediments, proving that seasonal thermal stratification in the Hongfeng Lake reservoir may be a key factor for the seasonal differences in methane emissions.
The enrichment of Methanosaeta, a specialized acetic acid trophic methanogenic archaea, was observed in the sedimentary columns during summer and winter. The fractionation coefficient results showed that the methane production pathway in the sedimentary columns of Hongfeng Lake Reservoir was mainly acetic acid trophic, and the methane production trend in this pathway was greater in summer than in winter. There is a very active methane anaerobic oxidation process in the sediment column of Hongfeng Lake reservoir in summer, and the methane production potential of Hongfeng Lake sediment in summer is lower than in winter, while the methane anaerobic oxidation potential in summer is slightly higher than in winter.
Functional microbial abundance data indicate that coupled sulfate reduction AOM occurs in in-situ sedimentary columns during summer, and coupled metal iron reduction AOM occurs in shallow and deep layers during summer. In winter sedimentary columns, the iron reducing bacteria Bacillus, a participant in M-AOM, was significantly enriched in the bottom layer.

本研究致力于探究储层甲烷排放问题，尤其是阐明甲烷温室气体产生机制，揭示甲烷生成量的季节性通量变化，并为优化我国能源结构、节能减排的经济发展战略提供科学理论支持。本文综合运用地球化学与生物学方法，以季节性热分层作为关键切入点，从生物转化的视角研究不同热分层条件下储层沉积物中甲烷生成与氧化过程对甲烷时空动态变化的影响。对沉积柱剖面中甲烷生成/氧化功能微生物的生态位分布进行了精细研究，揭示了甲烷生成/氧化功能群的生态适应机制与生成/氧化效率。假设储层沉积柱剖面中甲烷溶解具有明显的季节性特征，红丰湖水库的季节性热分层可能成为季节性甲烷排放差异的关键因素。原位沉积柱中甲烷的产生与排放可能受其他电子受体的影响。
沉积柱中甲烷溶解的分布数据表明，储层原位沉积柱剖面中甲烷溶解具有明显的季节性特征，夏季沉积物中的甲烷代谢热区向上迁移。室内培养实验的结果进一步验证了沉积物中甲烷热区的分布变化，证明红丰湖水库的季节性热分层可能是导致季节性甲烷排放差异的关键因素。
在夏季和冬季沉积柱中，专门利用乙酸的产甲烷古菌 Methanosaeta 的富集现象被观察到。分数系数结果显示，红丰湖水库沉积柱中的甲烷产生途径主要以乙酸营养为主，且该途径的甲烷产生趋势在夏季较冬季更为显著。夏季红丰湖水库沉积柱中存在非常活跃的甲烷厌氧氧化过程，夏季红丰湖沉积物的甲烷产生潜力低于冬季，而夏季的甲烷厌氧氧化潜力略高于冬季。
功能微生物丰度数据显示，夏季原位沉积柱中发生耦合硫酸盐还原 AOM，夏季浅层和深层发生耦合金属铁还原 AOM。在冬季沉积柱中，参与 M-AOM 的铁还原菌 Bacillus 在底层显著富集。