五里峡水库初级生产力对水气界面二氧化碳和甲烷排放速率时空变化的影响

近年来水库温室气体备受关注,为揭示水库水气界面CO_2和CH_4在时间和空间上的变化特征,于2016年7~12月采用静态箱法在五里峡水库对其CO_2和CH_4排放速率进行4次监测,并测试微型光合生物初级生产力等.结果表明,五里峡水库夏季为大气CO_2的汇,变化范围在-30.14~-3.47 mg·(m~2·h)~(-1),秋、冬季均为大气CO_2的源,变化范围在15.57~115.06 mg·(m~2·h)~(-1).甲烷排放速率在夏季变化幅度明显,变化范围在0.08~1.03 mg·(m~2·h)~(-1),而在秋、冬季变化稳定,变化范围在-0.07~0.43 mg·(m~2·h)~(-1).受水库周期性蓄水和排水影响,CO_2和CH_4排放速率在空间上表现为水库消落带和坝尾较低而库区较高的分布格局.此外,CO_2和CH_4排放速率时空变化与微型光合生物初级生产力分别呈显著负相关和正相关(r为-0.477和0.771).这是因为产甲烷菌能够将夏季微型光合生物固定的有机碳转化成CH_4释放到大气中,从而使微型光合生物对水圈CO_2和CH_4循环产生负反馈效应和正反馈效应.因此,本研究结果为进一步评估微型生物对岩溶水体碳循环的贡献提供了理论依据.

Spatial-Temporal Variations of CO2 and CH4 Flux Through a Water-air Interface Under the Effect of Primary Productivity in Wulixia Reservoir

In recent years, the effect of greenhouse gas has been a focus. In order to reveal the spatial-temporal variations of CO₂ and CH₄ flux through a water-air interface, Wulixia reservoir was selected as a typical case for measuring CO₂and CH₄ flux using a floating chamber during four study periods in 2016.The primary productivity of the water was also studied. The results indicate that surface-layer water in Wulixia reservoir is a CO₂ sink in summer, varying between -30.14 and -3.47 mg·(m²·h)^-1. However, it is the source of CO₂ in autumn and winter, varying between 15.57 mg·(m²·h)^-1 and 115.06 mg·(m²·h)^-1. The variation of methane flux is obvious in summer, but it is stable in autumn and winter. The spatial distribution of CO₂ and CH₄ show that they are higher in the typical bay area and lower in the tailing dam as well as in the drawdown zone of the reservoir. In addition, the spatial and temporal variation of CO₂ and CH₄ are negatively and positively correlated with primary productivity (r -0.477 and 0.771), respectively. Due to the high activity of photosynthetic micro- organisms in summer, CO₂ can be sequestered, allowing the surface-layer water in Wulixia reservoir to be a CO₂ sink. In addition, methanogenic bacteria can oxidize organic carbon produced by photosynthetic micro-organisms. Therefore, CH₄ has a negative correlation with primary productivity. The results provide important information for the study of microorganism functions in karst water systems.