Diurnal variation characteristics of <i>p</i>CO<sub>2</sub> in the summer water column of Gaoyang backwater area in Pengxi River, Three Gorges Reservoir

Abstract

水柱中CO₂分压(pCO₂)的时空分布在一定程度上可反映水中碳的环境地化特征.本研究在夏季分层期间对三峡水库澎溪河(小江)流域高阳回水区段进行了昼夜连续观测发现,恒定的温跃层中pCO₂随水深增加而显著增大,表层0.5 m处pCO₂均值为152±71μatm,而在水深10.0 m处pCO₂均值为4568±1089μatm,同水温、pH及DO存在明显的负相关关系,进一步分析认为水温等将影响微生物、浮游植物的代谢过程及水气界面对流传输,进而对pCO₂分布产生影响.对水气界面CO₂扩散通量的估算结果表明,夏季分层期间高阳水域总体上表现为CO₂的汇,其对大气CO₂的吸收量最大值于15:00左右,达到-0.33 mmol/(m²·h);最弱在次日凌晨3:00左右,吸收量仅为-0.17 mmol/(m²·h).;Partial pressure of CO₂ (pCO₂) in water column was an importamt indicator for the geochemical characteristics of carbon. Diel samples for pCO₂ and other environmental factors, i. e. pH, DO and water temperature, was taken from Gaoyang backwater area in the Pengxi (Xiaojiang) River, Three Gorges Reservoir in every 6 h. Results showed that in stable metaliminon, vertical pCO₂ increased along with the water depth. Mean value of the pCO₂ at 0.5 m depth was 152 ± 71 μatm, while that of pCO₂ at 10.0 m depth was 4568 ± 1089 μatm. Significant negative correlations between pCO₂ and pH, DO, water temperature were detected, indicating metabolism of microbial and planktonic community and penetrative convection were impacted by water temperature that regulated the distribution of pCO₂. Estimation of the water-air flux of CO₂ indicated that the general characteristic of carbon sink in the Gaoyang backwater area was obvious. A maximum sink flux of -0.33 mmol/(m²·h) was detected in 15:00 while a minimum sink flux of -0.17 mmol/(m²·h) was also detected in 3:00 of the next day.