内蒙古河套盆地地表水-浅层地下水化学特征及成因

地表水-地下水的相互作用不仅影响地下水化学演化，而且控制地下水化学组分的空间分布，是地下水研究领域的重要课题之一。在内蒙古河套盆地采集地下水样品58组，雨水和地表水样品32组，分析了主要离子、微量组分和氢氧稳定同位素等18个指标。结果表明，研究区地表水除了受蒸发浓缩作用影响外，还受到人为活动的影响，水中钙离子、硫酸根、硝酸根等组分明显升高。浅层地下水具有与地表水类似的主要组分和同位素特征，表明浅层地下水可能受到地表水的影响。地表水补给进入含水层的过程中，可能发生了硅酸盐矿物的非全等溶解、盐岩全等溶解、重晶石沉淀、硝酸根、铁氧化物矿物和硫酸根还原等作用。其中，铁氧化物矿物的还原是地下水砷含量高的主要原因。此外，砷浓度还受硫酸根还原的影响。因此，地下水-地表水的综合研究有助于揭示地下水的成因及水文地球化学过程。

Characteristics and Their Causes of Surface Water-Groundwater Geochemistry in the Hetao Basin,Inner Mongolia

Surface water-groundwater interaction, which not only affects groundwater chemical evolution, but also controls spatial distribution of groundwater components, is one of the important issues in the groundwater field. Fifty-eight groundwater samples and thirty-two rainwater and surface water samples were taken from the Hetao basin, Inner Mongolia. Major components, trace elements and water isotopes were analyzed in those samples. Results showed that surface waters were affected by human activities and evaporation, which contained elevated concentrations of Na⁺, Ca²⁺, SO^2-₄, and NO^-₃. Shallow groundwater had the similar major components and isotopic characteristics with surface water, which indicated that shallow groundwater was affected by surface water. During the infiltration of surface water into the shallow aquifers, incongruent dissolution of silicate minerals, congruent dissolution of halite, barite precipitation, reduction of NO^-₃, Fe oxides and SO^2-₄possibly occurred. Reductive dissolution of Fe oxides was the major cause of high As concentration in shallow groundwater. Arsenic concentration was also affected by SO^2-₄ reduction. Therefore, synthetical investigation of surface water and groundwater would help to reveal hydrogeochemical processes in aquifers.