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全新世古洪水事件的重建是当前全球变化研究的一个热点.通过长江下游一个稳定江心洲上沉积剖面的粒度和有机元素组成分析,清晰地揭示出主要粒度参数、概率累积曲线和C-M图可以指示洪水事件沉积,而沉积有机质的TOC/TN因为反映大洪水期间,长江流域强烈的地表冲刷将大量降解不完全的碎屑有机质带入下游,也成为洪水事件的较好示踪标志.根据210Pb堆积速率,研究剖面的粒度及TOC/TN比值清晰地记录了长江干流1850～1954年期间的若干次特大洪水事件,与历史文献和水文监测资料吻合.然而自20世纪60年代以来,长江流域人类活动显著增强,尤其是大量水坝兴建,将大量粗颗粒泥沙和沉积有机质蓄积在水库中,而显著改变长江下游干流的悬浮沉积物粒度和有机质组成,因而难以可靠地指示近50年来的洪水事件.
The reconstruction of the Holocene flood events is a hot spot in the current global change research.According to the analysis of grain size and organic element composition of a stable sedimentary section in the lower reaches of the Yangtze River, the main grain size parameters, probability cumulative curves and CM maps can be clearly indicated to indicate the flood events Sediment, while the deposition of organic matter TOC / TN reflect the flood during the intense surface erosion in the Yangtze River Basin will be a large number of incomplete degradation of organic matter into the downstream debris, flood events have also become a good marker.According to 210Pb deposition rate, The particle size and TOC / TN ratio of the study section clearly recorded several extraordinary flood events of the Yangtze River from 1850 to 1954, consistent with historical documents and hydrological monitoring data. However, human activities in the Yangtze River Basin have been significantly enhanced since the 1960s In particular, the construction of a large number of dams has resulted in the accumulation of a large amount of coarse-grained sediments and sedimentary organic matter in the reservoirs, significantly changing the suspended sediment grain size and composition of organic matter in the mainstream of the lower reaches of the Yangtze River, making it difficult to reliably indicate flood events in the past 50 years.