乌江流域下游梯级水库沉积物中木质素的特征及有机碳来源辨析

Characteristics of lignin in sediment cores from cascade reservoirs downstream of the Wujiang River and source analysis of organic carbon

以位于中国西南喀斯特地貌乌江流域下游的两座大型深水水库(思林水库、彭水水库)为研究对象,利用木质素生物标志物技术对沉积柱中的陆源有机碳(organic carbon,OC) 进行了定性分析和定量计算.研究结果表明:木质素含量指标∑8 值在 0.55~2.97 mg/10 g dw (dry weight,干重)之间,A8 值在 0.38~1.42 mg/100 mg OC 之间;木质素母源植被信息显示,沉积柱中的木质素主要来源于被子植物的草本组织;木质素受白腐菌和棕腐菌共同作用,发生较低程度的去甲基/去甲氧基以及侧链氧化降解.端元模型结果显示,沉积柱中外源有机碳的贡献总体上略大于内源有机碳,其中土壤有机碳贡献最大.河流梯级筑坝作用对沉积物中有机碳的影响表现为外源有机碳的拦截和内源有机碳的积蓄两个方面,并且内外源有机碳分布存在明显的空间异质性.

The terrestrial organic carbon(OC) in sediment cores from two large deepwater reservoirs(Silin and Pengshui) located in the lower reaches of the Wujiang River in the karst landscape of Southwest China were analysed and quantified using lignin biomarker technology.Qualitative analysis and quantitative calculations of terrestrial-derived organic carbon in sediment cores using the lignin biomarker technique showed that the lignin content index ∑8 ranged from 0.55 to 2.97 mg/10 g dw(dry weight) and A8 ranged from 0.38 to 1.42 mg/100 mg OC.The lignin in the sediment cores was derived mainly from the herbaceous tissues of angiosperms,and had been degraded via demethylation,demethoxylation,and oxidative degradation of the side chains by white rot and brown rot bacteria.The end-member model showed that the contribution of exogenous organic carbon to the sediment cores was slightly greater than that of endogenous organic carbon,with soil organic carbon contributing the most.The influence of river cascade damming on sedimentary organic carbon was manifested in the interception of exogenous organic carbon and the accumulation of endogenous organic carbon,and there was obvious spatial heterogeneity in the distribution of both types of organic carbon.