大同盆地地下水中溶解性有机质分子特征及其对砷迁移富集的影响

Molecular Characteristics of Dissolved Organic Matter and Its Impact on Arsenic Mobilization and Enrichment in Groundwater System in Datong Basin

为研究地下水中溶解性有机质(DOM)分子特征及其对砷(As)迁移富集的影响,以大同盆地为研究区,利用三维荧光和傅立叶变换离子回旋共振质谱(FT-ICR MS)方法,分析了沿地下水流动方向地下水中DOM的分子组成特征和差异,揭示了沿地下水流动方向地下水中DOM的变化对As迁移转化的影响机制。结果表明:从大同盆地山前倾斜平原至盆地中心冲洪积平原地下水中As浓度逐渐升高、SO_(4)^(2-)和NO~-_(3)浓度逐渐减少,且地下水中As浓度与DOC浓度之间存在正相关关系,表明有机质的微生物降解过程是控制地下水中As迁移富集的主要过程之一;从补给区到排泄区地下水中DOM的分子类型更加丰富,脂肪族类化合物减少,多环芳烃类化合物相对增加,有机质趋于大分子或难以降解,在热力学上更不易被微生物利用;从补给区到排泄区在微生物介导下DOM降解,为含砷铁氧化物还原性溶解提供电子,同时As(Ⅴ)被还原为As(Ⅲ)释放到地下水中,从而影响地下水中As的迁移富集。

In order to figure out the impact of molecular characteristics of Dissolved Organic Matter(DOM) on arsenic mobilization and enrichment in groundwater,the molecular composition characteristics and differences of DOM along groundwater flow in Datong Basin were characterized by three-dimensional fluorescence and Fourier transform ion cyclotron resonance mass spectrometry(FT-ICR MS),and the mechanism of DOM affecting arsenic migration and enrichment along the groundwater flow direction was revealed.The results are as follows:The concentration of arsenic gradually increases and the concentration of SO_(4)^(2-) and NO^(-)_(3) gradually decreases from the recharge zone to the discharge zone in Datong Basin,and there is a positive correlation between arsenic concentration and DOC concentration in groundwater,indicating that microbial degradation of DOM,which acts as a dominate host,promotes the release of arsenic mobilization and enrichment into groundwater;the types of DOM in groundwater are more abundant,aliphatic compounds are reduced,polycyclic aromatic compounds are relatively increased,and DOM tends to be macromolecular or difficult to degrade,and is less available to microbial degradation thermodynamically;DOM degradation is mediated by microorganisms to provide electrons for the reductive dissolution of iron oxides from the recharge zone to the discharge zone,while As(Ⅴ) is reduced to As(Ⅲ) and released into groundwater,which leads to arsenic mobilization and enrichment in groundwater.