长江中下游悬浮物稀土元素地球化学特征及其对三峡工程的响应

通过分析枯水季(2008年1月)长江中下游干流和支流(湖泊)悬浮物的稀土元素(REE)组成,探讨三峡水库的泥沙拦截对该区域沉积物组成和干、支流输沙关系的影响。结果表明:长江干流宜昌至城陵矶段的REE变异系数显著大于城陵矶以下站位,且部分站位出现显著的Ce或Eu异常,该段沉积物的物质组成存在显著差异;洞庭湖沉积物继承了长江干流的REE组成特征;鄱阳湖和汉江等支流(湖泊),与干流的REE组成存在一定的差异,通过端元混合模型估算得,观测期间鄱阳湖和汉江对长江干流沉积物的贡献分别约为58%和23%。由此可见,三峡水库的运行,导致了长江中下游枯季的物质来源和组成发生改变:中游河床出现了显著的侵蚀,汉江和鄱阳湖等支流(湖泊)对干流的物质输送相对增加。

Geochemical Characteristics of Rare Earth Elements in Suspended Sediments of Middle and Lower Reaches of the Yangtze River and Their Responses to the Operation of the Three Gorges Reservoir

Nineteen suspended sediment samples from the mainstream and seven suspended sediment samples from tributaries were collected in the middle and lower reaches of the Yangtze River during the dry season (January, 2008), Rare Earth Elements (REEs) in these samples were characterized to discuss the influences, including composition and provenance changes, of sediment retention by the Three Gorges Reservoir (TGR). The results show that:the coefficient of variation (CV) of REEs in suspended sediments between Yichang and Chenglingji were significantly greater than that of after Chenglingji, and obvious anomalies of Eu and Ce occurred at some sites between Yichang and Chenglingji, suggesting that sediment compositions changed significantly by the TGR. REEs characteristics in sediments of the Dongting Lake inherited those of mainstream Yangtze River. In terms of the sediment provenance, the Poyang Lake and the Hanjiang River contributed respectively about 58% and 23% sediment of the mainstream during the observation period. All above results indicated that the provenance and composition of suspended sediments in the middle and lower reaches of the Yangtze River were changed due to the sediment retention of the TGR. It is to say that, downstream of the TGR, the riverbed erosion occurred significantly and sediment contributions from downstream tributaries to the Yangtze River increased.