Study On Riverine Carbon Flux And Erosion Of Zhujiang (Pearl) River Drainage Basin

This paper researches on the water and suspension in Zhujiang (Pearl) River and her three branches, sampling in Makou Hydrological gorge station of Xijiang River, Hekou Hydrological gorge station of Beijiang River and Boluo Hydrological gorge station of Dongjiang River. The author calculated the riverine carbon flux and measured the content of different carbon forms and carbon isotope composition. Furthermore, the author also studied drainage basin erosion and the influence of vegetation distribution on erosion. The main conclusions are as follows:The HCO3- ion content of Zhujiang River changes notably in one hydrological year, especially in wet season and dry season. As for the content of inorganic carbon, that of the Xijiang River is the highest, then the Beijiang River, and then the Dongjiang River. The Xijiang River's inorganic carbon source was major from karst process in the drainage basin. Due to the "washing effect" , the content of HCO3- ion increased in the wet season. The HCO3- of Dongjiang River originates mostly from the weathering process of silicate, and its content changes little. The HCO3-of Beijiang River originates primarily from the weathering process of silicate and karst process. Influenced by the " dilution effect" , its content decreased while its runoff increased.The content of dissolved organic carbon (DOC) in Zhujiang River only reached the lowest value standard only in the tropical-subtropical zone. Among the three rivers, the DOC content of Dongjiang River is the highest, then the Beijiang River, and then the Xijiang River.Paniculate organic carbon (POC) content of Zhujiang River is lower than that of other rivers in the world. Among the three branches, the content in Xijiang River is the highest, then the Dongjiang River, and then the Beijiang River. The runoff of Zhujiang River has very great seasonal change. DOC and POC increased dramatically at high runoff in these rivers. The DOC content increased 20-90%, POC content probably increased 6 times. This indicates that Zhujiang River has the characteristics of mountainous rivers.The riverine carbon flux of the Zhujiang River is about 1.355 104kg-km-2-a- in hydrological year 2000-2001, lower than the result in hydrological year 1997-1998. It was due to fewer storms and lack of stronger erosion process.The stable isotope value of POC in Zhujiang River is between -18~-28%. The stable isotope value of POC in the three hydrological station sections in the normal season is between -23.09 %~-20.66%, -27.25%~-18.77% and -24.10%~-21.83%, respectively. The change in scope of POC 8 13C value in the wet season is between 23.75%~- 22.59%, -25.36%-~-22.65% and -23.17%~--20.80%. The POC 13C value in the period of the transition from the wet season to the dry season is between -22.95%~-20.32%, -24.39%~~-22.13% and -24.39%~-22.31%, respectively. The change in scope of POC 13C value in the dry season in the three hydrologicalstation section is between -23.15% ~-20.06%, -24.34%~-22.87% and -26.67%~-23.60%, respectively.The seasonal change of POC 13C value of suspension in Zhujiang River is the reflection of the suspended source in every season. POC in the Dongjiang river was influenced mainly by C4 plant such as grass and crops, and POC 6 13C value was heavier than that in the Xijiang and Beijiang Rivers. The forest cover rate of the Beijiang River drainage basin is higher. Affected by C3 plant, its POC 8 13C value was lighter. Influenced by C3 and C4 plant in the Xijiang River, its POC 6 13C value is between Dongjiang and Beijiang Rivers'.The POC14C apparent age of Zhujiang River suspension is between 540 and 2050 a. Among the three branches, Xijiang and Beijiang River suspensions are older. The 14C apparent age value of Dongjiang River is comparatively scattered-it not only has considerably younger samples but also the older ones. POC of Zhujiang River was mainly from modern carbon, the content of which was fairly constant in different branches all year round.The erosion of Zhujiang River drainage basin is relativel...