太湖典型湖区沉积物外源有机质贡献率研究

采用稳定同位素示踪法，分析了太湖竺山湾和南部湖区苕溪港区域表层沉积物碳和氮同位素分布特征，并利用“端元混合法”计算确定了陆源输入对湖泊沉积物有机质的贡献. 结果表明:① δ13C值在南部湖区要高于竺山湾，竺山湾表现为从河道(-27.72‰)到湾内(-23.00‰)逐渐增大的趋势，南部研究区域也表现出同样的趋势，说明外源有机质的贡献不断减少；② δ15N值在陆源有机质中较低，而在内源有机质中较高，没有明显的梯度变化规律；③ C/N比表现为从外源到内源不断减小的趋势；④ 利用“端元混合法”计算外源有机质贡献率发现，δ13C和C/N比的结果较为相似:竺山湾入湖口的外源有机质贡献率为46.51%～52.51%，竺山湾外源有机质贡献率为27.61%～30.85%；而δ15N计算得到的外源有机质贡献率差异较大，竺山湾入湖口处为56.91%～97.47%，竺山湾为74.83%. 讨论认为含氮物质的多来源特征及N同位素分馏作用的复杂性都增加了有机质源解析的不确定性. 

Contribution Rate of Exogenous Organic Matter in Sediments from Typical Areas of Taihu Lake

Surface sediments were sampled selectively in the Zhushan and Southern Tiaoxi bays of Taihu Lake.The isotope tracer technique was employed to analyze carbon and nitrogen isotope distribution in the surface sediments of the two lake areas.Furthermore,the contribution of terrestrial sources to the sediments of the lakes was obtained using the "end-member mixture method".Carbon isotope analysis results revealed that the value of δ13 C was higher in the southern parts of the lake than in Zhushan bay.It increased gradually from the channel(-27.72‰) to the bay(-23.00‰) in Zhushan bay,and the southern part showed a similar pattern.This indicated that the exogenous organic matters were reduced from the channel to the center of the lake.Nitrogen isotope analysis results showed that δ15 N were low in exogenous organic matter,while it was high in endogenous organic matter.However,because of the complexity of the nitrogen sources,there was no obvious gradient variation between two lake areas.The C /N ratio decreased from exogenous sources to endogenous sources,which also implied the reduction of the contribution from exogenous organic matters.The contribution of exogenous organic matter calculated by the"end-member mixture method"indicated that the results of δ13 C and C /N were similar.The contribution of exogenous organic matter was 46.51%-52.51% in the lake inlet and 27.61%-30.85% in the Zhushan bay.The calculated δ15 N values showed great differences;the contribution of exogenous organic matters was 56.91%-97.47%in the lake inletand 74.83%in Zhushan bay.It is believed that maltiple sources of nitrogenous compounds and the complexity of nitrogeu isotop fractionation in biogeochemical process will increase the uncertainty in the ideutification of te sources of organic matters.