北京水源地水体中颗粒有机质的碳氮同位素研究

Stable carbon and nitrogen isotope composition of particulate organic matter in water source of Beijing

对北京潮河、白河和密云水库水体中悬浮颗粒物和表层沉积物的稳定碳、氮同位素及其来源进行了分析.结果表明,研究区内冬季水体中悬浮颗粒物的δ13C值比夏季的偏负,其变化范围分别为-30.75‰～-25.75‰(冬季)和-29.34‰～-25.91‰(夏季);δ15N值冬季较夏季偏正,其变化范围分别为-0.83‰～9.67‰(冬季)和-0.96‰～6.73‰(夏季),季节性变化较明显.表层沉积有机质的δ13C值较悬浮颗粒有机质偏正,分布范围是-27.25‰～-21.58‰.悬浮物与颗粒有机质(POC)含量之间呈指数负相关关系,表明陆源土壤侵蚀是悬浮物的主要组成部分.悬浮颗粒有机质夏季主要来源于C3植物降解的土壤有机质(SOM-C3)和水生植物,而冬季水生藻类的贡献增大.表层沉积物的主要来源是SOM-C3.δ15N体现的是物源信息和一系列生物地球化学过程综合作用的结果.仅用δ15N不足以准确辨析物质来源,但能够较好地指示特殊的生物地球化学过程.

Samples of suspended particulate matter and sediments were collected in water source in northern Beijing and analyzed for carbon and nitrogen isotopic compositions.These isotopic compositions and C/N ratios were used in identifying the origins of particulate organic matter.It was found that the carbon and nitrogen isotopic ratios in suspended particulate matter were-29.34‰～-25.91‰ and-0.96‰～＋6.73‰,respectively,in summer,while they were-30.75‰～-25.75‰ and-0.83‰～＋9.67‰,respectively,in winter.There were obvious seasonal variations in isotopic compositions observed in the study area.The ratios of stable carbon isotope of surface sediments varied from-27.25‰ to-21.58‰.The relationships between SPM weight and POC indicated that mineral matter coming from the erosion of terrigenous soils was the main component of SPM.The suspended particulate organic matter was derived mainly from SOM-C3 and macrophyte in summer,while it was derived from plankton in winter.Surface sediments organic matter was derived mainly from SOM-C3.δ15N ratios reflected the combined results of information of sources and a series of biogeochemical processes.Although δ15N ratios could provide limited information of sources,it can be used to trace some special biogeochemistry processes.