蓄水初期三峡水库草堂河水-气界面CO_2和CH_4通量日变化特征及其影响因素

Diurnal variation and influencing factors of carbon dioxide and methane emissions at water-air interface of Caotang River,Three Gorges Reservoir in the initial impoundment period

为查明三峡水库蓄水初期典型支流水-气界面CO_2和CH_4通量的日变化特征,采用LGR在线分析仪-通量箱法,于2015年9月初在库腹一级支流草堂河回水区开展连续24 h的定位观测.结果表明,24 h监测期内,支流库湾水-气界面CO_2通量变幅为-81.642~180.991 mg/(m^2·h),呈"昼吸夜放"特征,均值为17.346 mg/(m^2·h),总体为释放特征;CH_4全天均表现为释放状态,释放通量均值为0.064 mg/(m^2·h),呈"昼弱夜强"变化.相关分析结果表明,CH_4和CO_2释放通量与风速呈正相关,与表层水温、溶解氧浓度、叶绿素a浓度呈负相关,说明风速物理扰动、浮游植物光合作用是控制草堂河水-气界面气体通量最重要的环境因素.同时,干-支流相互作用形成的特殊水环境(如异重流、水温分层)也与水-气界面温室气体通量过程密切相关,但是其作用机制更为复杂,应开展进一步系统观测和深入研究.

With the LGR- floating chamber method, a 24-hour continuous monitoring was carried out in the initial impoundment period of Three Gorges Reservoir, in order to understand the greenhouse gases fluxes （carbon dioxide and methane） across the wa- ter-air interface of Caotang River which is the primary tributary of the reservoir. The results indicated that the fluxes of carbon diox- ide and methane across the water-air interface appeared an obvious ebaractefstic of diurnal variation. The fluxes of carbon dioxide ranged from -81.642 to 180.991 mg/（ m2 ~ h） , and the average fluxes of carbon dioxide were 17.346 rag/（ m2 ~ h）. As a result, the overall carbon dioxide showed ＂absorb by day and emit at night＂. Methane was emitted all day with the average fluxes of meth- ane 0.064 mg/（ mz ~ h） showed ＂strong at day and weak at night＂. The fluxes of carbon dioxide and methane had a positive con＇e- lation with wind speed while a negative correlation was observed with water temperature of surface layer, dissolve oxygen and chlo- rophyll-a. It could be explain the most important factors that influence emissions at water-air interface were phytoplankton photosyn-thesis and bacterial metabolism process in the surface water. The changes in greenhouse gases emissions at water-air interface were also relevant to special environment （density current and thermal stratiflcation） due to the interaction between main current and tributaries. The hydrodynamic factors were the key factors that affect carbon cycle and the greenhouse gases fluxes across the water- air interface in backwaters of tributaries, which would be worth researching.