三峡水库正常蓄水后支流沉积物的污染特征

为研究三峡水库不同时期沉积物污染变化规律,采集三峡库区175 m正常蓄水后7条支流表层沉积物样品,分析营养盐、重金属含量和污染特征,结果表明:7条支流表层沉积物均存在营养盐含量超标现象,但仍处于多数底栖生物可承受水平,其中龙溪河21号断面w(TN)和19号断面w(TP)最高,分别为1.97、2.03 g/kg；采用EF(富集因子)和RI(潜在生态风险指数)评价了重金属富集程度和污染水平,重金属EF表现为Hg>As>Cd>Pb>Cu>Zn>Mn>Cr,仅Mn和Cr的EF小于1,未受污染；RI平均值为160±35,处于中度生态风险. 沉积物中TN、TP来源以农业面源污染为主,TOM主要来源于浮游动物和浮游植物；重金属污染则以流域工业污水排放和农业活动为主. 研究显示,三峡库区蓄水后沉积物中营养盐和重金属含量总体呈上升趋势,建议划分优先控制区域,重点解决农业面源污染,强化农村生活污水治理,并以严格的环境准入制度防控和削减流域工业污染. 

Analysis of Pollution Characteristics of Surface Sediments in Three Gorges Reservoir after Normal Impoundment

Abstract: Surface sediment samples were collected from seven tributaries of the Three Gorges Reservoir Region, which had been filled to a water depth of 175 m, to study the characteristics of the pollution caused by the sediment over time. The analysis of the nutritive salts, heavy metal contents and pollution characteristics indicated that the nutritive salt contents of the surface sediments from the seven tributaries exceeded the limits, though the majority showed acceptable levels of benthos. The total nitrogen content, w(TN), at the No. 21 section of Longxi River and the total phosphorus content, w(TP), with the highest values at the No. 19 section, were 1.97 and 2.03 g/kg, respectively. The enrichment factor (EF) and the potential ecological risk index (RI) were used to evaluate the heavy metal enrichment and pollution levels. The result was Hg>As>Cd>Pb>Cu>Zn>Mn>Cr in terms of the EF; only the EFs of Mn and Cr were smaller than 1.0. The averages of the RI values of the heavy metals were 160±35; this indicated a moderate ecological risk. The analysis of the sediment pollution sources showed that, in the surface sediments deposited on the tributaries'' riverbeds, the nitrogen and phosphorus pollutants mainly originated from agricultural non-point source pollution, TOM was mainly contributed by the zooplankton and phytoplankton, and heavy metal pollution was caused primarily by the discharge of industrial sewage and agricultural activities in the catchment areas. After the reservoir began to store water, the contents of nutrients and heavy metals in the sediments all showed an overall upward trend. Based on the analysis, suggestions for the pollution control were made as follows:delimiting priority areas for pollution prevention and control, focusing the efforts on solving agricultural non-point source pollution, improving domestic wastewater disposal in rural areas, and controlling and reducing industrial pollution by establishing a strict environmental access system.