渭河陕西段潜流带沉积物重金属变化初步分析

Variation of heavy metal concentrations in hyporheic sediments for the Weihe River of Shaanxi Province

为厘清潜流带沉积物重金属时空变化及与水量交换、沉积物颗粒结构间的关系,于2013年春夏两季对渭河陕西段5个研究断面66个测试点位沉积物的野外原位渗透系数、颗粒粒径、重金属含量进行分析.结果表明:影响渭河沉积物渗透系数的主要因素是沉积物粒径,同时沉积物垂向分层、排列组合也影响其渗透性能;沉积物重金属Cu、Zn、Pb、Cd质量分数在垂向上不同深度其含量大小不同,在时间上总体呈现春季>夏季,富集系数(EF指数)分析结果显示春季Cu、Zn(除华县)、Pb(除眉县)、Cd富集严重且主要受人为输入源影响,夏季除Cd元素外,Cu、Zn、Pb的EF值均<1.5,说明其含量主要来源于地壳和岩石圈的自然风化过程;Pearson相关分析发现粘土与粉砂(粒径<0.075 mm)百分比与沉积物重金属质量分数呈弱相关,重金属粒径效应不显著,粒径不是控制重金属含量的主要环境影子;对单一重金属垂向不同深度含量进行相关性研究发现除Cd外,其余3种重金属在垂向上的相关系数均>0.5(p<0.01),说明单一重金属在垂向上具有同源性且存在相互迁移与转化.

Surface water and groundwater are two interconnected components of one single resource and mutually impacts their quantity and qualityin the hyporheic zone. Estimation of variation of heavy metal concentration in hyporheic sediments is of critical importance in integrated management of groundwater and surface water bodies and in maintenance of ecosystem health of a river catchment. As a case study of the Weihe River,stream water and groundwater are inherently connected and water quality is strongly interacted. In this regard,a total number of 66 test locations from 5 inverstigation sites including Meixian,Xianyang,Caotan,Lingtong and Huaxian were selected in the spring and summer seasons of 2013. The hydraulic conductivitiy,particle size and heavy metals content of sediment for each test location were tested and analyzed. The results demonstrated that the changes of hydraulic conductivities were mainly resulted from sedimentary size,vertical stratification and structure composition. The mass fraction values of heavy metal( Cu,Zn,Pb and Cd) varied both with depth and seasons. Generally,the calculated values of heavy metal mass fraction in the spring were greater than those in the summer. Furthermore,by comparing tested value with background values of each heavy metal using enrichment factor analysis method,it can be found that in the spring,Cu,Zn( except for Huaxian site),Pb( except for Meixian site) and Cd had higher values resulted from anthropogenic discharge.However,in the summer,the mass fraction values of Cu,Zn and Pb were less than 1. 5,which illustrated the significant influence by natural weathering processes of crust and lithosphere. Moreover,the percentage of clay and silt of sediment had a weak positive correlation with the mass fraction of heavy metals on the basis of Pearson regression analysis. The variation of heavy metal concentration was not fully resulted from sedimentary particle. Except for Cd,the regression coefficients for Cu,Zn and Pb were greater than 0. 5,which indicated that these heavy metals changed similarly with depth and evenmigrated and transferred together by hyporheic water exchange.