内陆盆地区高碘地下水的成因分析:以内蒙古河套平原杭锦后旗为例

The formation of inland-high-iodine groundwater:A case study in Hangjinhouqi,Hetao Plain

针对内陆盆地区高碘地下水的成因问题,在典型地区——内蒙古河套平原杭锦后旗系统采集了25个地下水样和3个地表水样,分析了地下水中的I、Na＋、Ca2＋、Mg2＋、Cl-、SO2-4、HCO-3、As、Fe、Br、pH、Eh等指标。应用因子分析和多元线性回归分析方法,对内陆盆地区高碘地下水的成因进行了分析。结果表明：地下水中碘含量为31.84~1 289.57μg/L,高碘地下水主要分布于研究区北部地下水流相对滞缓的排泄带附近、地下35m的范围内,水化学类型以碱金属非重碳酸型为主;地下水中碘可能来源于狼山中元古代狼山群沉积物或平原区第四纪浅层沉积物;沉积物中的Fe2O3和有机质在低Eh条件下（Eh〈-30mV）分别发生还原性溶解和分解,吸附在其上的碘随之被释放到地下水中。另外,沉积物中的碘在高Ca2＋和弱碱性条件下吸附作用较弱,这也间接促进了碘在地下水中的富集。相对而言,有机质分解更为普遍,但Fe2O3的还原性溶解对碘富集影响更为强烈。该成果进一步深化了对内陆盆地区高碘地下水形成机制的认识,并为当地饮水安全和生态安全提供科学依据。

The survey of Hangjinhouqi,one of the high-arsenic and iodine groundwater regions in Hetao Plain,has been conducted,aiming at the formation of inland-high-iodine groundwater.The results based on 25groundwater samples and 3surface water samples showed that the concentration of iodine in groundwater samples ranges from 31.84μg/L to 1289.57μg/L.High-iodine groundwater mainly distributes in the north discharge area of groundwater in the study area with slow flow and strong evaporation within 35m underground.Furthermore,most of the high-iodine groundwater belongs to the alkali metal but nonbicarbonate type of water.Factor and regression analyses identified that the main factor,the desorption of iodine,plays an important role in the enrichment of iodine in groundwater.Iodine may come from the sediments in Langshan or the plain.Under reduction condition,Fe2O3is dissolved and organic matter is decomposed;Iodine in Fe2O3is desorbed into the groundwater;adsorption of iodine in sediments weakens in the condition of high-Ca2＋and low-Eh（Eh〈-30mV）.Iodine desorbed gets together in the discharge area of groundwater,forming the high-iodine groundwater.The decomposition of organic matter occurs widely in Hangjinhouqi,while the reducing dissolution of Fe2O3is more important for the aggregation of iodine in groundwater.The results not only make a better understanding of the genesis of high-iodine groundwater,but also provide a scientific basis for the safety of local drinking water.