甘肃省榆中盆地地下水化学演化特征及控制因素

Characteristics and controlling factors of chemical evolution of groundwater in Yuzhong basin

文中对榆中盆地地下水进行系统采样分析的基础上,对比历史水化学数据,对盆地地下水化学演化进行了深入分析。结果表明:研究区地下水化学类型相对复杂,HCO3-Ca·Mg型、HCO3·SO4-Ca·Mg、Cl·SO4-Ca·Mg型等均有分布。沿着地下水流向,在溶滤、阳离子交替以及蒸发浓缩作用下,盆地地下水由南部的HCO3·SO4-Ca·Mg型水向北逐渐演变为Cl·SO4-Na·Mg型水,TDS含量也随之升高,盆地南部和中部为TDS含量小于1g/L的淡水,至宛川河河谷南侧演化为TDS含量3~5g/L的咸水。对比1979年水化学数据,研究区地下水氯离子和硝酸根离子含量明显增加,地下水TDS含量和总硬度总体上呈上升趋势,地下水水质向盐化和硬化方向演变;表征天然地下水化学状态的重碳酸型水范围逐渐缩小,而受人类活动影响的氯化物硫酸型水范围逐渐增加。研究区水化学组分受硅酸盐岩和碳酸盐岩风化溶解共同作用,在蒸发浓缩作用下富集。

20 groundwater samples were collected from Yuzhong Basin and analyzed for their chemical compositions,and chemical characteristics of groundwater in Yuzhong Basin were studied.The results indicated that the HCO3-Ca·Mg,HCO3·SO4-Ca·Mg and Cl·SO4-Ca·Mg are distributed.Along the flow direction of groundwater,under the action of dissolution and filtration,cation alternation and evaporation concentration,the groundwater gradually evolves from HCO3·SO4 Ca·Mg in the south to Cl·SO4-Na·Mg in the north,and the TDS content also increases.The fresh water in the south and middle of the basin evolve into saline water with TDS content of 3-5 g/L in the south of the Wanchuan River Valley.Comparing with the 1979 hydrochemical data,the groundwater chloride and nitrate ion contents increase significantly,the groundwater TDS content and total hardness show overall upward trends,and the groundwater quality changes to salinization and hardening.The range of bicarbonate water,which is characterized by the chemical state of natural groundwater,gradually narrows,while the range of chloride-sulfuric acid water,which was affected by human activities,gradually increases.The hydrochemical components are enriched by evaporation and concentration under the combined action of weathering and dissolution of silicate rocks and carbonate rocks.