Control factors of pCO₂ and CO₂ degassing fluxes from the Yellow River in autumn

The partial pressure of CO₂(pCO₂) in the water of the Yellow River was directly measured in November 2006,and the distribution and dynamics of pCO₂ are discovered in the combination of the related parameters.The results indicate that the pCO₂ in the surface water ranges between 80 and 166 Pa,with an average value of 110 Pa,and is lower than that in other important rivers in the world.Furthermore,the significant variations in the spatial pCO₂ distribution,i.e,the pCO₂ value in the middle part of the river is higher than upstream and downstream.Photosynthesis of phytoplankton has a slight effect on pCO₂, even though Chla reaches the maximum 3.58 μg/L at Baotou station where the pCO₂ value is still 91 Pa.Since the organic matter level in the Yellow River water is low and hard to degrade,the EpCO₂/AOU value just varies from 0.14 to 0.20 in the mainstream and reserwir,lower than the theoretical value of 0.62,which suggests that the biological aerobic respiration effect has little contribution to pCO₂.The content of TSS and DIC in the Yellow River water varies from 3.77 to 1308.33 mg/L and from 3.03 to 4.14 mmol/L,respectively,both of which are generally higher than other rivers in the world,and the maximum appears at Tongguan.Meanwhile the pCO₂ has a positive relationships with TSS,PIC and DIC.So the main control factors of pCO₂ are attributed to the carbonate system with high carbonate content induced by the strong mechanical erosion and chemical weathering in the Yellow River drainage area.Based on the model of wanninkhof and the wind speed,the released CO₂ from the Yellow River to atmosphere is estimated about 14.5×10⁸ mol in autumn at the rate of 0.229 μmol/(m²·s),which is equal to the CO₂ absorption of 8 250 km² grass or 112 kmz forest.CO₂ outgassing flux from the Yellow River is close to that of the Ottawa River and less than the Amawn River.