PENG Xi^{1, 2}, LIU Cong-qiang¹, WANG Bao-li¹＊, ZHAO Yan-chuang^{1, 2}, Wang Fu-shun³

(1.State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China;
2. University of Chinese Academy of Sciences, Beijing 100049, China; 3.School of Environmental and Chemical Engineering, Shanghai University, Shanghai 200444, China)

Abstract: In order to understand the diffusion characteristics of CO₂ in the river-reservoir system after damming, the Liuchonghe River, Hongjiadu Reservoir and Hongfenghu Lake which are  different in trophic levels were investigated during May, 2011 to May, 2012. The basic physical, chemical and biological factors and the isotopic composition of dissolved carbon dioxide (δ¹³C_DIC) in these surface waters were measured, too. pCO₂ and the exchange flux of CO₂ (CO₂ flux ) through the water-air interface were calculated. The average pCO₂ in the Liuchonghe River, Hongjiadu Reservoir and Hongfenghu Lake were 684±195μatm, 884±484μatm and 592±596μatm, respectively, which were the carbon source relative to atmospheric pCO₂. The pCO₂ was affected differently by algal activity in the Liuchonghe River, Hongjiadu Reservoir and Hongfenghu Lake. The pCO₂ had different biweekly changes in the Liuchonghe River, Hongjiadu Reservoir and Hongfenghu Lake, and so did the CO₂ flux. The Hongfenghu Lake, of the highest primary productivity, behaved as a carbon sink during May, 2011 to September, 2011, and the average CO₂ flux was -5.70 mmol·m^-2·d^-1. δ¹³C_DICand pCO₂ changed synchronously, indicating that the biogeochemical process controlled the spatiotemporal change of pCO₂ in surface water. The necessity of high monitoring for estimating the CO₂ flux in the river-reservoir system was accurately explained.

Key words: diffusion flux of CO₂; primary productivity; damming;  Wujiang River system