银川平原水化学特征分析

Analysis of characteristic of Hydrogeochemistry in Yinchuan plain

基于银川平原的水文地质条件,对研究区的地下水环境综合指标与地下水化学类型进行了分析:EC值与DO值呈负相关关系,随着含盐量的增高,EC值增高,DO值减小;TDS与EC之间存在较好的正相关性,水中溶解的盐类越多,水的TDS值越高,水的导电性越好,其电导率EC值越大。阳离子平均浓度由大到小为Na^+>Ca^(2+)>Mg^(2+)>K^+>NH_4^+,阴离子平均浓度由大到小为HCO_3^->SO_4^(2-)>Cl^-。研究区地下水类型以HCO_3·SO_4—Ca·Mg、HCO_3·SO_4—Ca·Na、HCO_3·SO_4—Na·Mg,以及SO_4·HCO_3—Na·Mg等类型为主。活度系数与离子强度呈反比,即离子强度升高导致水溶液中的离子浓度和电荷量升高,离子重新组合成溶质,导致离子活度系数下降。研究区内方解石最接近于平衡状态,可能存在于含水层环境中。对地下水环境综合指标和各组分浓度以及研究区水化学的形成环境进行分析可知:位于研究区中南部的65号点属于SO_4·Cl—Na型水,受污染的可能性大;而在其南部的4、83、290号点,由于位于黄河灌溉区,受地表水的影响增强,地下水污染程度较65号点低。

Based on the hydrogeological conditions of Yinchuan plain, the groundwater environmental comprehensive index and groundwater chemical types were analyzed： There is a negative correlation between DO and EC,the study also shows the positive correlation between EC and TDS,the increase of dissolved salts in groundwater leads to the increase of TDS,which makes the conductivity of groundwater and EC increased.The sort of average concentration of cation is Na＋ 〉Ca2＋〉 Mg2＋〉K＋〉 NH4＋,and the sort of average concentration of anion is HCO3- 〉SO42- 〉Cl-. The groundwater chemical type of study area mainly include：HCO3·SO4—Ca·Mg,HCO3·SO4—Ca·Na,HCO3·SO4—Na·Mg,SO4·HCO3—Na·Mg. The study shows a negative correlation between activity coefficient and ionic strength： the increase of the ionic strength leads to the increase of the ions concentration and the charge in groundwater,which causes the ion to be reassembled into the solute,which leads to the decrease of activity coefficient of ionic. Calcite is closest to the equilibrium state in the study area,and it may exist in the aquifer environment. Based on the groundwater environmental comprehensive index and the concentration of each component, we can conclude from the groundwater chemical evolution environment of the study area： The No. 65 sample locates in the south of study area,and its groundwater chemical type is SO4·Cl—Na,it has a high risk to be contaminated; The sample of No. 4,No. 83,No. 290,which locate in the south of No. 65 and the Yellow River irrigation area,surface water has a more significant influence on groundwater,the pollution level of those samples is lower than No. 65 sample.