新疆阿克苏地区平原区高砷地下水分布特征及富集因素分析

地下水砷污染是全球化环境问题.本文基于阿克苏地区平原区2017年75个地下水砷实测含量进行分析.结果表明,研究区地下水砷含量变化范围为ND—98.70μg·L^-1,平均值为9.42μg·L^-1,超标率达26.7%.水平方向上,高砷地下水主要集中在研究区的中部偏南一带;垂直方向上,山麓斜坡冲洪积砾质平原潜水区地下水砷含量平均值表现为深层潜水>浅层潜水,中下游河流冲积平原区承压水区地下水砷含量平均值表现为深层承压水>浅层承压水>潜水.采用绘制Piper三线图、Gibbs图、离子比例图等方法对研究区地下水砷的富集因素进行研究.结果表明,研究区地下水砷主要为自然来源;封闭的地质构造和造山带与河流等沉积环境相结合的水文地质条件有利于研究区地下水砷的富集;研究区高砷地下水水化学类型主要为HCO3·SO4-Na,还原性-弱碱性环境利于地下水砷富集;研究区地下水砷受强烈的蒸发浓缩作用进一步浓缩,同时地下水阴离子浓度增大加剧了地下水中阴离子与砷酸根、亚砷酸根之间的竞争吸附,利于地下水砷的富集.

Spatial distribution and enrichment factors of high-arsenic groundwater in the plain area of Aksu Prefecture,Xinjiang

Groundwater arsenic pollution is a global environmental problem. This paper analyzed arsenic concentration of 75 sampling wells in 2017 in plain area of Aksu Prefecture. The results showed that the concentration of arsenic in groundwater ranged from ND to 98.70 μg·L^-1, the average concentrations of 9.42 μg·L^-1, over the standard rate of 26.7%. In the horizontal, the high-arsenic groundwater mainly concentrated on mid-south in the study area. In vertical direction, the arsenic concentration in deep unconfined groundwater was higher than that in shallow unconfined groundwater in piedmont slope alluvial gravel plain area. The arsenic concentration of groundwater in alluvial plain area of middle and lower reaches was manifested as deep confined groundwater>shallow confined groundwater>unconfined groundwater. The Piper trilinear diagram, Gibbs diagram, and ion ratio diagrams were used to study the factors of arsenic enrichment in groundwater. The results showed that the groundwater arsenic was mainly caused by natural factors. The closed geological structure and the hydrogeology of the orogenic belt combined with the sedimentary environment of rivers were conducive to the enrichment of groundwater arsenic. The hydrochemical types of the high-arsenic groundwater was mainly HCO3·SO4-Na, and the reductive-weak alkaline environment of groundwater contributed to the enrichment of arsenic. Arsenic concentration was increase further by evaporation and concentration, the increase of anion concentration exacerbated the competitive adsorption between anions and arsenate and arsenite in groundwater, conducive to enrichment of groundwater arsenic.