三峡库区澎溪河回水区溶解态金属离子来源和时空分布特征分析

摘要: 以三峡库区北岸最大支流澎溪河的高阳平湖段为例，探讨随着调水方式导致的水位变化，三峡库区支流金属离子Ca、Zn、Fe、Cr、Pb、Cu和Hg等在时间、水平和垂直空间维度上的分布和动态．在2013年6月5日～2014年5月29日为期1a的采样周期内于澎溪河长年回水区高阳平湖的4个采样点采样共21次，平均每17.3d采集一次．水体样品分别采自水体表层(0～0.5m)、中层和底层(底泥以上0.5m)冬季水体不分层期间，中层样品采自水深1/2处，分层时则采自温跃层．应用ＲBＲ-80220型水质自动分析仪监测各样点水温、电导率、水深等数据．水样采用冷原子吸收法和电感耦合等离子体原子发射光谱法(ICP-AES)测定各金属质量浓度．运用Excel、SPSS软件进行数据统计分析;以Hg离子为例，利用Matlab软件构建各水位时期金属离子质量浓度分布三维柱状图．结果表明:①从水体可溶性金属离子质量浓度角度，澎溪河水质总体较好，Cr、Pb、Cu、Zn和Hg等离子均低于地表水环境质量标准(GB3838-2002)Ⅲ类水质标准相应离子质量浓度;②在来源上，Cr、Pb和Cu等离子来源于干流回水;Fe和Zn离子来源于澎溪河内源;Hg离子来源受干流回水和内源影响．金属离子随着温度分层出现质量浓度分层现象;③影响高阳平湖电导率的主要物质是非金属离子．

关键词: 三峡库区; 澎溪河; 回水区; 金属离子; 时空分布

Abstract: This study uses the Gaoyang Lake section of the Pengxi River, the largest tributary on the northern bank of the Three Gorges Reservoir ( TGR) , as an example for exploring the distributions and dynamics of Ca ，Zn, Fe, Cr, Pb, Cu, and Hg ions in thetributaries of   TGR where the water level fluctuates due to dam regulation.   Samples were taken 21 times, once every 17.3 days, at foursampling sites in Gaoyang Lake, which is in a perennial backwater zone of the Pengxi River, during one year from June 5, 2013 to May29, 2014. At each sampling site, water samples were taken from the surface layer ( 0 -0. 5 m)   middle layer, and bottom layer (0.5m above the bed mud) . During winter when the water was not stratified, the middle layer samples were taken at 1/2 depth, and whenwater was stratified in other seasons, the middle layer samples were taken from the thermal layer. Inductively coupled plasma atomicemission spectrometry (ICP-AES) and cold-vapor atomic absorption methods were adopted to determine the concentrations of the metals. Excel and SPSS were used for data analysis and Matlab for building 3-D prisms displaying concentration distributions of Hg ionsin the high water level   period ( 175m, November-April in the ensuing year) , sluicing period ( May-middle June) , low water level in the flooding season ( 145 m, June-August) ，and the storage period ( September-November).    The results provided the followingobservations ① Concentrations of Cr, Pb, Cu, Zn, and Hg ions were lower than those in Class Ⅲ of the water environment qualitystandard ( GB 3838-2002). ② Cr, Pb, and Cu had high peak values during the storage and sluicing period, and the lowest valuesduring the high water level period. Cr, Pb, and Cu were derived from the main stream of   Yangtze, while Fe and Zn were from thePengxi River locally. The concentration of Hg ions was affected by both the main stream and endogenous sources. As the water column stratified, metal ions did not mix among the stratified layers in Gaoyang Lake.   ③ The conductivity was significantly lower during thehigh water level period than during other water level periods. The main material that affects the conductivity of Gaoyang Lake could benonmetallic ions．

Key words: Three Gorges Reservoir; Pengxi River; backwater area; metal ions; spatial and temporal distribution