桂江流域河流有机碳特征

Characteristics of Riverine Organic Carbon in Guijiang Watershed,Guangxi

通过对桂江流域内植物、土壤碳同位素、河流有机碳含量及同位素进行系统取样测试分析发现,桂江流域C3植物的δ13C范围为-37.89‰^-23.27‰,C4植物δ13 C范围为-14.49‰^-12.00‰。土壤碳库的δ13 C范围为-30.43‰^-11.56‰,平均值为-24.32‰。土壤碳库主要受C3途径植物控制,C4途径植物对土壤碳库的δ13 C影响有限,植物残体转化成土壤有机质的过程中产生有机碳同位素分馏效应,造成土壤有机碳同位素比植物碳库偏重4.42‰。桂江河流DOC分布范围0.68~2.16mg/L,平均值为1.39mg/L。ρ(POC)分布范围0.11~1.14mg/L,平均值为0.37mg/L,DOC/POC的范围1.31~9.04,ρ(DOC)>ρ(POC),成为水体有机碳的主要形式。流域水体中δ13CDOC值的范围为-29.682‰^-15.377‰,平均值为-24.810‰;δ13CPOC值的范围为-27.886‰^-24.271‰,平均值为-25.868‰;两者均位于土壤有机碳库同位素范围内,说明河流有机碳主要来源于土壤的机械侵蚀和土壤有机质的降解,受人类生产生活有机废弃物和河流自生浮游植物的代谢分泌物影响小。

Abstract： After systematic sampling and analysis of the carbon isotope in plant and soil, riverine organic carbon and isotope in Guijiang watershed, Guangxi Province, it is found that the carbon isotopic （δ13C） values in C3 plant is ranging from - 37. 89‰ to - 23. 27‰, in C4 plant ranging from - 14. 49‰ to -12.00‰, and in soil is ranging from -30.43‰ to -11. 56‰0, with an average value of -24.32‰. Soil carbon pool is mainly affected by C3 plant, while C4 plant has limited effect to the soil carbon pool. There is an organic carbon isofope fractionation in the process of plant organization transforming into soil organic matter, resulting organic carbon isotope in soil that is 4.42 ‰ heavier than that of plant carbon pool. The content of dissolved organic carbon（DOC） in Guijiang River ranges from 0.68 to 2.16 mg/L, with an aver- age value of 1.39 mg/L. The content of particulate organic carbon（POC） ranges from 0.11 to 1.14 mg/L, with an average value of 0.37 mg/L. The ratio of DOC/POC ranges from I. 31 to 9.04, so the content of DOC is greater than the POC, being the main form of organic carbon in riverine water. The carbon isotope of dissolved organic carbon （DOC） rangs from - 29. 682‰ to - 15. 377‰, with an average value of - 24. 810‰. The carbon isotope of particulate organic carbon （POC） rangs from -27. 886‰ to -24. 271‰ ,with an average value of -25. 868‰. Both are located in isotope range of the soil organic car- bon pool, indicating that riverine organic carbon comes mainly from mechanical erosion of the soil organic matter and soil degradation, with very limited effect from organic waste by human production activity and metabolic secretions by river authigenie phytoplankton.