Abstract: Wujiang River，originating from Yungui Plateau，is an important tributary of the Yangtze River.It is a typical karst river in southern China with karst landform developed considerably.The partial pressure of CO2 (〖WTBX〗P〖WTBZ〗CO2) and the “breath” flux of the stream water in Wujiang basin were discussed based on the field riverine data of certain physical and chemical parameters，such as temperature (T)，dissolved oxygen (DO)，alkalinity (ALK) and pH in the stream water.The value of 〖WTBX〗P〖WTBZ〗CO2 was at the range of the data from 291.3 μatm to 1 530 μatm in stream water and the mean value was 9493 μatm，which was 3 times more than that of atmosphere ambience.And the mean value of 〖WTBX〗P〖WTBZ〗CO2 was 9924 μatm in the tributaries，which was slightly more than that of 902.6μatm in mainstream.Thus it can be deduced that the Wujiang stream water is a source for CO2 in atmosphere in low flow season.The obvious spatial variation of 〖WTBX〗P〖WTBZ〗CO2 in the mainstream was caused by the characteristics of basin reaches and human activities.The unapparent negative relationship between 〖WTBX〗P〖WTBZ〗CO2 and DO in low flow season showed that heterotrophic respiration in the riverine water was not the main source of the riverine DIC (dissolved inorganic carbon) in Wujiang River.The sources of Wujiang riverine DIC were considerably complicated for there were likely many riverine DIC sources in the stream water.The spatial distribution of 〖WTBX〗P〖WTBZ〗CO2 was the result of the import of karst surface water and groundwater as well as the oxidation and decomposition of organic matter.

Key words: Wujiang River, karst basin, riverine “breath”, dissolved oxygen (DO), the partial pressure of CO2 (〖WTBX〗PCO2)