关键词: 长江, 黄河, 沉积物, 金属, 地球化学, 形态

Abstract: The Changjiang River and the Huanghe River are the two longest rivers in China. The differences between them, such as climatic conditions and bedrock compositions, have caused the differences of metal geochemistry in their sediments. Therefore, sediment samples were taken from the mainstreams of the rivers, and the total contents and speciation of 16 metals (Li,Na,K,Ca,Sr,Ba,Ti,V,Cr,Mn,Fe,Co,Ni,Cu,Zn and Al) have been analyzed, in order to reveal their differences and the relationships in the geographical and geological conditions. Eleven sediment samples were taken from the Changjiang River and other ten samples were from the Hanghe River. The speciation method was after Tessier et al., and five forms of metals were fractionated: ① exchangeable, ② carbonate, ③organic, ④ Fe/Mn oxide, and ⑤ residual. Total contents and contents of the five forms were detected by ICP AES. The total contents of metals in the two rivers are consistent with their crustal abundances. The coefficients of variances of all the elements under study are quite small, which is caused by the transportation and dispersion processes of sediments along the mainstreams. Mobile elements, such as Na, Sr, and Ca, have significantly negative correlations with the immobile elements in sediments of the Changjiang River which is caused by the strong weathering forces inside the watershed. By the weathering forces, mobile elements are removed from the sediments, and immobile elements are relatively enriched. However, such a kind of relationship has been weakened in the Huanghe River due to the relatively poor weathering forces. Ca and Mn have the lowest percentages of the residual form in both rivers, while the other elements have rather high contents of the residual form. The significant differences between the two rivers have also been revealed by the speciation study. The residual forms of most of the metals have lower percentages in the Changjiang River than those in the Huanghe River. However, the non residual forms of the metals in the sediments of the Changjiang River tend to reside in the Fe/Mn oxide and organic forms. These results are also in line with the stronger weathering forces in the Changjiang River watershed than those in the Huanghe River area. The sediments in the Huanghe River mainly consist of loess, and the loess contains quite little organic matter, which is another reason for the low contents of organic forms of metals in sediments of the Huanghe River.

Key words: Changjiang River, Huanghe River, sediments, metals, geochemistry, speciation