河套盆地晚更新世以来黄河改道对高砷地下水分布的控制机制

Mechanism of Yellow River diversion in controlling high arsenic groundwater distribution since Late Pleistocene

针对河套盆地开展了历时多年的水文地质环境地质调查,利用采集的298组浅层地下水样品以及收集并甄选的382个水文地质钻孔记录分析发现:河套盆地内95%的高砷地下水(As质量浓度>10μg/L)集中在黄河决口、改道形成的古河道影响带及黄河决口扇裙带。其中,盆地南部首次发现了较为集中的高砷地下水,其分布范围与黄河北岸的晚更新世以来黄河决口、改道形成的4个大型决口扇,在空间上有着良好的对应关系。黄河古河道带及决口扇裙带表现为较强的还原环境及蒸发浓缩作用以及较弱的地表水补给强度。受pH值、含铁氧化物的还原性溶解等因素影响,决口扇裙带浅层地下水中砷的含量略低于平原中部黄河古河道带。结果表明:黄河古河道带及决口扇裙带特定的沉积环境控制着地下水的水文地球化学过程,进而对高砷地下水的分布具有决定性的作用。

A series of hydrogeological survey and environment geology survey on Hetao basin has been carried out for many years.Two hundred and ninety-eight groundwater samples from the shallow aquifer and three hundred and eighty-two hydrogeological borehole loggings were collected,and it was founded that 95%of samples had high arsenic groundwater(As>10μg/L)in the Hetao basin and were distributed in the paleochannel zone and flood fans of Yellow River.The high arsenic groundwater distribution was discovered in the southern Hetao basin,and the four flood fans formed by bursting,diversion of ancient Yellow River course since the Late Pleistocene has an corresponding relationship with spatial variability of high arsenic groundwater.The paleochannel zone and flood fans of Yellow River represent hydrogeochemical characteristics of the strong reducing environment,serious evaporation,and the low infiltration recharge of surface water.Due to the influence of pH value and reductive dissolution of iron oxides,the arsenic concentration in flood fans was lower than those in the paleochannel zone of the Yellow River.Results show that:the sedimentary environment controlled the hydrogeochemical processes of the shallow aquifer and played a decisive role in the distribution of high-arsenic groundwater.