More global attention is being paid to hydrological regime, sediment and water environmental changes caused by resource development in the Lancang - Mekong River Basin. In this paper, Eight critical reaches along mainstream of the Lancang - Mekong River were chosen for bed loads sampling, and 5 heavy metal elements were tested in the laboratory to discuss their spatial changes and pollution assessment in the watercourse. Methods of Index of Geoaccumulation and Ecological Risk Index were employed to assess heavy metal pollution status in the mainstream of the Lancang - Mekong river. The results show that ( 1 ) the average concentration of the heavy metal elements Zn、Pb、As in the bed loads in the Lancang (Upper Mekong) river is 91.43 mg/kg 、41. 85 mg/kg、21. 84 mg/kg, respectively, greater than the average concentration of those heavy metal elements in the bed loads of the Mekong (Lower Mekong) river(68. 17 mg/kg 、28. 22 mg/kg 、14. 97 mg/kg) , the average concentration of Cr in the bed sediment of the downstream - Mekong river is 418. 86 mg/kg larger than that in the Lancang river where the average concentration of Cr is 42. 19 mg/kg, and Cr concentration reaches 762. 93 mg/kg at Luang Prabang and 422. 9 mg/kg at Pakse. The Cu concentrations of in the 8 samples are almost equivalent, though they are slightly low at Jiajiu as 11. 7 mg/kg and at the boundary 7 mg/kg. (2) The result of the Index of Geoaccumulation shows that the contamination induced with Zn, Pb and As in the Upper Mekong has exceeded the pollution standard, in which Pb and As are worse than Zn. However, Cr is the major pollutant in the Lower Mekong, especially at Luang Prabang and Pakse. (3) The Ecological Risk Index suggests that the potential ecological risk of heavy metal in the whole Mekong is light. Based on analysis above, we argue that the heavy metal pollution in bed loads caused by mining of mineral resources or geochemical background in the upper part of the basin has not led to transboundary pollutant issue, probably due to reservoir trapping and dilution along the river. This research and results could enhance the deficiency of study in heavy metal pollution in the whole Mekong River, as well as a reference for government to decision-making during resource utilization in the watershed.%国际河流澜沧江-湄公河流域资源开发引起的水文情势、泥沙和水环境变化一直是国际社会关注的重点.本研究选取了该河干流境内外8个关键河段的底沙进行采样,并进行5种重金属元素(锌Zn、铅Pb、铜Cu、铬Cr、砷As)含量实验测试,分析了该河干流底沙重金属含量空间变化.运用沉积学原理,应用地积累指数法和潜在生态危害指数法评价了澜沧江-湄公河流域干流底沙重金属污染的情况.结果显示:1.在澜沧江-湄公河流域干流底沙重金属元素中Zn、Pb、As在上游中国境内澜沧江底沙中的含量平均值分别为91.43 mg/kg、41.85 mg/kg、21.84 mg/kg,均大于其在下游境外湄公河底沙中平均含量,其平均含量分别为68.17 mg/kg、28.22 mg/kg、14.97mg/kg;Cr在境外湄公河底沙中含量的平均值为418.86mg/kg,大于境内上游澜沧江底沙中的平均含量42.19 mg/kg,且主要集中在琅勃拉邦和巴色采样点,其含量分别为762.93 mg/kg、422.9 mg/kg;Cu除在戛旧和界碑含量较小分别为11.7 mg/kg、7 mg/kg外,在上下游其他采样点的含量分布变化不明显.2.地积累指数法评价结果表明干流底沙重金属在上游中国境内Zn、Pb、As有污染,其中Pb、As的污染较Zn严重.在下游中国境外Cr污染较严重,其污染主要集中在琅勃拉邦和巴色两个采样点,As在巴色采样点也出现了轻微污染.3.潜在生态危害指数法评结果表明干流底沙重金属元素单一潜在生态危害系数和多种重金属潜在生态危害指数均较小,各采样点重金属潜在生态危害程度均属于轻微污染.由此可见澜沧江-湄公河境内局部河段因地球化学背景或矿产开采致使的水体和底沙重金属污染,沿程经水体稀释和水库淤积后,尚未出现污染的跨境迁移现象.本研究能在一定程度上填补澜沧江-湄公河流域在干流上对重金属污染研究的空缺,为澜沧江流域资源开发的评价影响提供理论依据.
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