关键词: 河床沉积物, 重金属, 污染评价, 澜沧江

Abstract:

Bed sediment is the main carrier of heavy metals in rivers. Its heavy metal content is an important indicator of heavy metal pollution in the water environment. This study investigates heavy metal contents of bed sediments along the mainstream of the Lancang River in Yunnan and Tibet and assesses their pollution risks. In recent years, the accumulation of heavy metals in the aquatic system of the Lancang River has become a problem. With increasing industrialization of the region, water quality of the Lancang River is in general declining and sediments in many river segments contain a high concentration of heavy metals that is higher than the background values. As an international river, Lancang river's water quality affects the relationship of the riparian countries. This article focuses on the following three aspects of heavy metal pollution in the river: the distribution of heavy metals in the sediments of the river basin; the enrichment factors of heavy metal pollutants at the sampling sites along the main river stream; and geoaccumulation of heavy metals in bed sediments. This study uses 22 sediment samples collected from different control sites in the river basin. These samples were analyzed using X-ray fluorescence (XRF) analysis at the laboratory of Yunnan University for the content of eight heavy metals (Cr. Mn, Ni, Zn, As, Pb, Cu, and Co). Background values of these heavy metals used in the assessment of river sediment pollution came from the database of background of elements in soils of China. Two assessment methods (sediment enrichment factor and geoaccumulation index) were employed to evaluate the severity of contamination of various heavy metals in the river. The results of these assessments show that (1) the average concentration of the heavy metals in most parts of the main river stream is at the safe level, but the concentration is high in the middle reach of the river between Jiuzhou and Gongguo Bridge, due to the high geological background and Zn-Pb mining in the Bijiang River basin; (2) the result of sediment enrichment factor analysis indicates that anthropogenic influences concentrate mainly in the middle and lower reaches of the river. Geoaccumulation index analysis also shows that Cu, Pb, Zn contents of the sediments are higher in the transitional area between the middle and lower reaches of the river; (3) dams block the transportation of sediments and make heavy metal pollution of sediments discontinuous along the river. Human activities such as urbanizaion also have a clear impact on the heavy metal pollution of the nearby river sediments. Urban development, mining, and dam building have played a significant role in heavy metal pollution of the Lancang River. A comprehensive investigation of heavy metal pollution should be performed in the middle reache area where the concentration of heavy metals is at a high level.

Key words: sediment, heavy metals, pollution assessment, the Lancang River