银川平原不同深度地下水化学演化特征研究

Hydrochemical Evolution Characteristics of Groundwater at Different Depths in the Yinchuan Plain

为探明银川平原不同深度(5~600 m)地下水化学特征及演化过程,采用地下水位动态分析方法、Person相关性分析、饱和指数和水化学方法(Piper图、Gibbs图、离子比例系数)对银川平原不同深度地下水化学特征和同位素特征进行了系统分析,并采用氚和^(14)C定年方法估算了浅层(5~30 m)和深层(150~600 m)地下水的年龄。结果表明:研究区5~30 m浅层地下水化学类型为Cl·SO_(4)-Na·Mg、SO_(4)·Cl·HCO_(3)-Na·Mg型,主要受蒸发浓缩作用影响,150~300 m、400~600 m深层地下水均为HCO_(3)·CO_(3)-Na·Mg、HCO_(3)-Na·Mg型,受岩石风化作用控制;5~30 m浅层地下水主要受引黄灌溉水补给,地下水年龄9~>68 a,150~600 m深层地下水来源于西部山区,年龄为7325~25554 a B.P.;地下水中离子主要来自碳酸盐岩、蒸发盐岩、硅酸盐岩的溶解,阳离子交换作用也影响地下水中化学组分的变化。

In order to explore the hydrochemical characteristics and evolution process of groundwater at different depths(5-600 m)in the Yinchuan Plain,a systematic analysis was conducted on the hydrochemical and isotopic characteristics of groundwater at 9 different depths in the study area by using groundwater level dynamics,Person correlation analysis,saturation index,and hydrochemical methods(Piper plot,Gibbs plot and ion ratio coefficient).Besides,the tritium and ^(14)C dating methods were used to estimate the ages of shallow(5-30 m)and deep groundwater(150-600 m).The results indicate that the chemical types of shallow groundwater in the study area are Cl·SO_(4)-Na·Mg or SO_(4)·Cl·HCO_(3)-Na·Mg,which are mainly affected by evaporation and fractional crystallization.Deep groundwater in 150-300 m and 400-600 m is HCO_(3)·CO_(3)-Na·Mg or HCO_(3)-Na·Mg,which are controlled by rock weathering.Isotopes indicate that shallow groundwater is significantly recharged by irrigation water,with groundwater ages ranging from 9 a to>68 a.Deep groundwater in 150-600 m originated from the western mountainous areas,with ages ranging from 7325 a to 25554 a.The ion ratio coefficient method and saturation index indicate that ions in groundwater mainly comes from weathering and dissolution of carbonate,evaporite,and silicate rocks.Cation exchange also affects the changes in chemical components in groundwater.