西江水体有机碳含量变化及悬浮物碳同位素的意义

Riverine Organic Carbon Content and Significance of Carbon Isotopic Composition in the Xijiang River,China

以西江马口断面水体为研究对象,讨论其有机碳含量、悬浮物同位素组成(δ13C、Δ14C)与环境之间的关系。西江马口断面有机碳含量呈现季节性变化,其中颗粒有机碳(POC)含量范围介于0.13～4.98 mg/L之间,溶解有机碳(DOC)含量范围介于0.98～4.17 mg/L之间,DOC/POC比值为1.34,远低于世界多数河流之比值。近年来马口断面悬浮物POCδ13C的变化范围介于-21.3‰～-26.1‰之间,随时间出现整体性漂移现象,表明流域生态环境整体改善。POCΔ14C变化范围介于-132‰～-425‰之间,与取样期间的流域降水过程及土壤的侵蚀相关。

This paper presents data of a 8-year time series of particulate organic carbon（POC） and dissolved organic carbon（DOC）,and isotopic composition（Δ14C,δ13C） of suspended sediment at Makou section of the Xijiang River.We also discuss the sources of suspended sediment,using natural 14C method.The results of organic carbon concentration show temporal variation.Among them,POC content ranges from 0.13 mg/L to 4.98 mg/L with the average value of 1.35 mg/L and DOC content range from 0.98 mg/L to 4.17 mg/L with the average value of 1.86 mg/L.The content of DOC is slightly higher than that of POC in most cases,indicating that POC produced by mechanical erosion is not dominant,while DOC resulting from decomposition of organic matter was dominant in the Xijiang River.The DOC/POC ratio is 1.34,higher than that of the Changjiang（Yangtze） River and the Huanghe（Yellow） Rivers.In recent years,suspended POCδ13C ranges from-21.3‰ to-26.1‰,showing drift phenomenon with the time,and indicating the overall improvement of the ecological environment in the Xijiang River basin.The suspended sediment Δ14C values ranges from-132‰ to-425‰,whose variation were closely related to soil erosion produced by precipitation during the sampling period.The deeper soil erosion contributes more to ＂negative＂ suspended sediment POCΔ14C value and aged organic carbon;while the shallow soil erosion contributes more to ＂positive＂ suspended sediment POCΔ14C value and young organic carbon.