新疆叶尔羌河流域平原区浅层地下水咸化空间分布及成因

Spatial distribution and cause of salinization of shallow groundwater in plain terrain of the Yarkant River Basin, Xinjiang

为了解新疆叶尔羌河流域平原区地下水咸化特征及成因,该文运用多元统计、地统计等方法并结合遥感技术和地球化学方法对浅层地下水(井深≤100 m)水质演化进行分析。结果表明,研究区地下水呈中性或弱碱性,水化学类型以HCO3·SO4-Ca·Mg、SO4·HCO3-Na·Ca、SO4·Cl^-Na·Ca(Mg)和Cl·SO4-Na型为主。咸化系数计算结果表明,单一结构潜水咸化程度较高,承压水区潜水咸化程度相对较低,浅层承压水咸化程度最高。潜水和浅层承压水Cl^-、SO4^2-、溶解性总固体(TDS)半变异函数分析表明,各指标的空间相关性较强;沿地下水流向,潜水Cl^-、SO4^2-、TDS浓度总体呈现升高的趋势,浅层承压水则呈现高低值相间分布的特征。因子分析和聚类分析表明,地下水咸化的影响因素可分为水文地质条件控制(GW1)、地下水化学环境影响(GW2)和人为活动影响(GW3)3类。GW1类地下水分布范围较广,离子浓度主要受蒸发岩矿物的溶解控制;GW2类地下水分布于草地,地下水化学环境对地下水咸化影响相对较大;GW3类地下水主要分布于耕地和建设用地,地下水咸化受人为活动的影响显著,潜水受到农业灌溉、生活污水和工业污水影响较大,浅层承压水受污染程度相对较低。

In order to understand the characteristics and causes of groundwater salinization in the plain area of Yarkant River Basin,the water quality evolution of the shallow groundwater(buried depth≤100 m)was analyzed by means of multivariate statistics,geostatistics,remote sensing technology and geochemical methods.The groundwater pH value ranged from 6.91 to 8.07,which mainly occurred under neutral to alkaline environment in the study area.Groundwater types in single structure unconfined groundwater were mainly HCO3·SO4-Ca·Mg,SO4·HCO3-Na·Ca,and unconfined groundwater in confined area were SO4·Cl^-Na·Ca and SO4·Cl^-Na·Mg,while Cl·SO4-Na,SO4·Cl^-Na·Ca and HCO3·SO4-Ca·Mg were dominant in shallow confined groundwater.The calculation results of salinization coefficient(SC)showed that the proportion of SC≤1,between>1 and 2,>2 in the water samples with single structure unconfined groundwater(17 groups of groundwater samples)were 47.06%,29.41%and 23.53%,respectively,and the degree of salinization was high.The proportion of SC≤1 in unconfined groundwater of confined area(22 groups of groundwater samples)was 50.00%.The proportion of Sc between>1 and 2 was 36.36%,the proportion of SC>2 was 13.64%,and the degree of salinization was low.The SC≤1,>1-2 and>2 of shallow confined groundwater(33 groups groundwater samples)was 42.43%,15.14%and 42.43%respectively,which the salinization degree was the highest.Kolmogorov-Smirnov tests were carried out on Cl^-,SO4^2-,TDS of unconfined and shallow confined groundwater,and the results obeyed normal distribution.To examine the degree of spatial correlation,the ratio of nugget to sill was advised generally.The nugget/sill≤0.25,>0.25-0.75,and>0.75 were the conditions in which spatial structures were supposed to be strong,moderate,and weak,respectively.In this study,the ratio of nugget to sill for all parameters of Cl^-,SO4^2-,TDS of unconfined and shallow confined groundwater were<0.25,suggested the strong spatial correlation for the studied regionalized variable.The trend of Cl^-,SO4^2-,TDS in unconfined groundwater was generally low in the South and high in the North,while that of shallow confined groundwater was characterized by the distribution of high and low values.Factor analysis was carried out on 14 hydrochemical indices of 72 groups of groundwater samples.The results showed that the contribution rates of main factors F1,F2 and F3 were 49.383%,19.528%and 13.520%respectively,and the contribution rate of cumulative variance was 82.431%.Cluster analysis showed that GW1(controlled by hydrogeological conditions)groundwater accounted for 58.33%of the all groundwater samples,which was widely distributed and mainly affected by natural processes.The saturation indices(SI)of carbonate minerals tended to be saturated,while the SI of evaporite minerals was unsaturated.The ion concentration was mainly controlled by the dissolution of evaporite minerals.GW2(affected by groundwater chemical environment)groundwater accounted for 15.28%,mainly distributed in grassland,and hydrochemical environment had a relatively large impact on groundwater salinization.Sodium adsorption ratio(SAR)was positively correlated with total dissolved solids(TDS)(R^2=0.770),which showed that Na+in groundwater had obvious ion exchange with Ca^2+ and Mg^2+ in aquifer medium.26.39% of the all groundwater samples belong to GW3(affected by human activities),mainly distributed in cultivated land and construction land,and groundwater salinization was significantly affected by human activities.Unconfined groundwater was greatly affected by agricultural irrigation,domestic sewage and industrial sewage,however,the pollution degree of shallow confined groundwater was relatively low.