三峡库区典型河流水-气界面CO2通量日变化观测及其影响因素分析

为研究河流水-气界面CO_2通量的季节和日变化特征;于2016年7月15～17日以及2017年11月4～6日对三峡库区嘉陵江支流竹溪河进行定点定时采集表层水样,并同步监测关键环境因子,采用亨利定律结合薄边界层模型计算其水-气界面CO_2通量F(CO_2).结果表明,竹溪河表层水CO_2分压p(CO_2)及界面CO_2脱气通量呈现出显著的日间和季节变化,以及明显的日内变化特征:在上午09:00前后达到释放高峰,随后波动下降;水-气界面CO_2通量日间均值分别为(100. 9±31. 6)、(78. 6±12. 1)、(83. 9±29. 7)、(137. 5±42. 1)、(147. 6±34. 0)、(132. 4±21. 7) mmol·(m~2·d)~(-1);并表现出夏季表层水体CO_2释放通量明显低于秋季,其均值分别为(87. 8±27. 5) mmol·(m~2·d)~(-1)和(139. 2±34. 0) mmol·(m~2·d)~(-1);总体表现出大气CO_2源的特征.竹溪河p(CO_2)和F(CO_2)受到诸多环境因子的影响,相关分析表明,pH、碱度、水温和气温是主要环境影响因子,CO_2释放通量可以用pH和碱度预测.

Daily Variation of CO2 Flux at Water-Air Interface and Analysis of Its Affecting Factors in a Typical River of the Three Gorges Reservoir

Diurnal and seasonal characterization of CO₂ partial pressure p(CO₂) and CO₂ areal flux F(CO₂) at the water-air interface in an anthropogenic river in the Three Gorges Reservoir area was studied. A tributary of the Jialing River in Chongqing Municipality was chosen, and daily and seasonal samples were taken in summer and autumn, focusing on riverine p(CO₂), F(CO₂), and their associated controls. Henry''s law combined with the thin boundary layer model was adopted to estimate the CO₂ flux via the water-air interface. The results indicated that F(CO₂) was not high on average, namely (87.8±27.5) mmol·(m²·d)^-1 and (139.2±34.0) mmol·(m²·d)^-1 in summer and autumn, respectively. The water-air interface F(CO₂) showed significant hourly, daily, and seasonal variations. CO₂ release peaked around 09:00 and then slightly decreased. We also found that pH, alkalinity, water, and temperature were significantly related to p(CO₂) and F(CO₂), whereas pH and alkalinity were the best predictors of F(CO₂). This study aids understanding of the impacts of urbanization on CO₂ emissions in the rivers and helps to re-evaluate local riverine CO₂ budgets.