内蒙古河套平原典型高砷区地下水中砷的演化规律

Geochemical evolution of high arsenic groundwater in a typical area of the Hetao Basin,Inner Mongolia

通过对高砷地下水典型区完整地质单元不同深度含水层地下水进行监测,分析了与砷释放、迁移和富集有关的敏感因素(水位、Eh、总铁、亚铁等)的时间和空间变化规律,探讨了高砷地下水的形成机理。结果发现,地下水灌溉区和黄河水灌溉区,地下水水位均受人为灌溉活动的影响。地下水砷含量在空间和时间尺度上发生有规律的变化。在空间尺度上,地下水中砷含量随着深度的增加而升高,井深小于10 m的地下水砷含量在1.88~2.58μg/L;井深在10~15 m之间的地下水中砷含量在18.2~217μg/L;井深在15~25 m之间的地下水中砷含量在38.3~226μg/L。受人为灌溉影响,地下水中砷的含量会随着地下水位的抬升而升高。地下水砷含量随时间变化的原因是水位抬升使水位变化造成氧化还原环境改变。地下水系统中含砷铁氧化物矿物的还原性溶解、脱硫酸作用等是控制地下水砷含量的主要水文地球化学过程。

Based on monitoring of groundwater levels and chemical conponents at different aquifers in a typical hydrogeological section of the Hetao basin, spatial and temporal variations in As, redox-sensitive parameters （including Eh, total dissolved Fe, Fe （ Ⅱ ）） were assessed, and the formation mechanisms of high As groundwater were evaluated. Results showed that groundwater levels were affected by agricultural irrigation in both groundwater irrigation area and surface water irrigation area. Spatial and temporal variations of groundwater As were observed. Spatially, groundwater As concentrations increased with the increasing sampling depths. In aquifers at depths 〈 10 m, groundwater As was less than 5.0μg/L, between 18.2 and 217 μg/L at depths 10 - 15 m, and between 38.3 and 226μg/L at depths 15 - 25 m. Affected by agricultural irrigation, groundwater As generally increased with the increase in groundwater levels. The reason for the increases in As concentrations with increasing water levels is that the fluctuation of groundwater level induced the change of groundwater redox conditions. The major hydrogeochemical processes controlling groundwater Asconcentrations included reductive dissolution of Fe（Ⅲ ） oxides and bacterial sulfate reduction.