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The Contents and Mineral and Chemical Compositions of Suspended Particulate Materials in the Yangtze River, and Their Geological and Environmental Implications
详细信息   
摘要
The contents and mineral and chemical compositions of the SPM in the Yangtze River were determined using the samples from hydrological stations in the mainstream and the major tributaries during 2003～2007 in order to investigate systematically the spatial and temporal variations of mineral and chemical compositions in the Yangtze River SPM and their geological and environmental implications.An average SPM content of 256.5mg/L obtained in this study is moderate compared with that in world large rivers. Large spatial and temporal variations of SPM contents were observed in the Yangtze River, corresponding to the changes of flow speed, flowthrough and SPM supply, which are affected by the factors, such as the slope of the river bed, local precipitation, weathering intensity, erosion conditions and anthropogenic activities. The SPM of the Yangtze River consists of clay minerals, clastic silicate and carbonate minerals, some heavy minerals, with minor iron hydroxide and organic compounds. A comparison study of the mineral composition of SPM in the Yangtze River and that in the Yellow River indicates that the chemical weathering activity in the Yangtze River area is much more intensive than that in the Yellow River area, and the physical weathering activity in the Yangtze River area is less intensive than that in the Yellow River area. From upper reaches to lower leaches, the contents of clay and clastic silicate in the Yangtze River SPM increase gradually, but the content of carbonate minerals decrease gradually, corresponding to the wetter and hotter climate and more intensive chemical weathering in the middle and lower reaches. In comparison with the upper crust rocks, the SPM in the Yangtze River has lower contents of SiO2, CaO, K2O and Na2O and higher contents of TFe2O3, reflecting preferential loss of Si, Ca, K and Na and enrichment of Fe in chemical weathering processes of silicates. In comparison with the average of world rivers and the Yellow River, the SPM of the Yangtze River shows lower contents of SiO2 and Na2O, indicating its higher intensity of chemical weathering. Compared with the sediments of the river beds, the Yangtze River SPM has lower contents of SiO2 and Na2O, and higher contents of Al2O3, K2O, MgO and TFe2O3, reflecting the enrichment of the smaller particles of clay and iron hydroxide in SPM. From the upper reaches to lower reaches, the CaO and MgO contents in SPM decrease gradually, but the content of SiO2 increase gradually, corresponding to the increase of clay minerals and decrease of the carbonates. ,The Co, Ni, Cu, Zn, Pb and Cd contents in the Yangtze River SPM are all higher than those of the upper crust rocks, which may be caused by their preferential adsorption by clay mineral in weathering processes. High Cu, Pb and Zn contents in SPM of Panzhihua, Yibin, Jiujiang, Datong and Nanjing stations may be related to the local mining activities. Remarkable high Cd anomalies are found in the Fushun and Changsha stations during July 2005. Compared with the bed sediments, the Cu, Zn, Pb and Cd contents in the Yangtze River SPM are several times to several tens of times higher, probably reflecting more intense mining activities in recent years, which should be considered in evaluation of the long term environmental variation of the drainage area. In comparison to the average global shale, the SPM of the Yangtze River has slightly higher ΣREE content and shows a small enrichment of light REE, reflecting probably the effect of the light REE enriched mineral deposits that are widely distributed in the Western Sichuan mountain area.

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