中文摘要：

为了探讨西江河口段表层水体CO_2分压（P_co2）的分布特征，于2006年秋季在西江磨刀门至马口河段沿程实测了58个样点的表层水体理化参数，结果表明，河道表层水体P_co2值介于93.15～334.38Pa之间，平均值为174.00Pa，被测河段是个明显的大气CO_2“源”河流水体的理化性质在向海输送过程中发生了明显的改变，并且导致表层水体P_co2随航程的增加而递减，样点水体接受的日照时间与其P_co2有负相关关系，使得表层水体P_co2呈现出日周期变化，河段表层水体P_co2的这种时空变化与河 口过程中河-海作用的弱化而引起水体理化参数（如水温、pH值、电导率、总溶解固体、氧化还原电位和碱度等）的变化以及水体内部碳的生物化学过程（如光合作用与呼吸作用以及有机物的分解转化等）密切相关。

英文摘要：

Field measurements were taken to determine the varying characteristics of the partial pressure of CO_2 （P_co2） in the Xijiang River inner estuary. Physicochemical parameters were measured in 58 surface water samples collected from different sites along the waterway from the Modaomen to the Makou gauge station in fall, 2006. The surface water P_co2 ranged hetween 93. 15 and 334.38 Pa with an average of 174.00 Pa, indicating that the surveyed waterway was a ＂source＂ of atmospheric CO_2. The p_co2 showed a decreasing trend with distance along the waterway from the Modaomen to the Makou gauge station, which was caused by the longitudinal variation of physicochemical parameters, while a negative correlation between pCO_2 and duration of sunshine resulted in diurnal variations of P_co2. The spatio-temporal variations of P_co2 were closely related with the variations of water physicochemical parameters such as temperature, conductivity, total dissolved solids, oxidation-reduction potential, alkalinity and pH, which are caused by the weakening river-sea interactions, as well as carbon biogeochemical processes such as photosynthesis, respiration and decomposition of organic materials within the water.