江汉平原地下水中氮素与砷迁移富集的相关性研究

Analysis of Relationship between Nitrogen and the Migration and Enrichment of Arsenic in Groundwater in the Jianghan Plain

通过采集江汉平原潜江和监利两个典型地区的77个地下水样品进行分析测试,对该地区高砷地下水的水化学成分以及地下水中硝酸盐、氨氮与砷之间的相关关系进行了分析,并研究了硝酸盐、氨氮控制的氧化还原环境对地下水中砷(As)迁移富集的影响。结果表明:江汉平原地区地下水水化学类型主要为HCO3-Ca·Mg型,地下水中低Eh值,低含量DO、NO-3、SO2-4和高含量的NH+4、S2-表明地下水为强还原环境;地下水中不同形态的氮对砷的迁移富集具有重要的控制性作用,当地下水中的NO-3含量较高时,地下水处于氧化环境,此时吸附在铁锰氧化物表面或与铁锰氧化物结合的砷不能释放到地下水中,从而呈现出地下水中砷含量随NO-3含量的增加而减少的趋势;地下水中砷含量与NH+4/NT比值具有良好的正相关关系,当地下水中NH+4/NT比值逐渐增高时,表明地下水处于还原环境,此时铁锰氧化物和氢氧化物发生还原性溶解,并释放出大量的砷进入地下水中。

This paper collects and tests 77 groundwater samples from Qianjiang and Jianli in the Jianghan plain and analyzes relationship between NO3^--N,NH4-N and arsenic,and then studies the impact of oxida- tion-reduction environment controlled by NO3^- and NH4^＋ on the migration and enrichment of arsenic. The results show that groundwater is mainly of HCO3-Ca · Mg type with low Eh value,low concentration of DO,NO3^- ,SO4^2- and high concentration of NH4^＋ ,S^2- ,which indicates the groundwater is in strong reduction environment. Different species of nitrogen in groundwater play an important role on controlling the migration and enrichment of arsenic. Groundwater with higher NO3^- concentration is in oxidation environment. Arsenic is absorbed on the surface of Fe-Mn-oxide or combined with Fe-Mn-oxide and the content of arsenic is in negative correlation with NO^3- concentration;meanwhile,NH4^＋/Nx values and As concentration have a well positive relationship. When the value of NH^＋/NT gradually increases, groundwater environment becomes reducing,which leads to the reductive dissolution of Fe-Mn-oxyhydroxideplays（oxides） and large amounts of arsenic release into groundwater.