硝酸盐输入对地下水系统中砷迁移富集的影响研究

The Datong Basin is located in the arid and semi-arid area in northern China. The groundwater quality has been deteriorating continuously in the area under the impact of both natural and human processes. The wide distribution of high arsenic groundwater is a major challenge for sustainable development at Datong. On the basis of the well understanding hydrological structure and hydrochemical processes prevailed within an arsenic and nitrate combined contaminated aquifer, this project aims to reveal the contaminants experience the complicated physical, chemical and biogeochemical processes in the spatial and the time successions. The impact of nitrate input on arsenic mobilization and enrichment is studied through comparison of the hydrochemical characteristics and microbial community structure with and without the presence of nitrate. Works including groundwater monitoring, column and batch experiments, biotic experiments and hydrochemical model studies are conducted to achieve the above aims. This study provides a better understand of the mechanism that high arsenic groundwater generation and has promise for explaination the controlling processes on arsenic mobilizaiton and enrichment in the groundwater system in a typical agriculture cultivated area. The study results can provide scientific supports regarding to arsenic contaminated groundwater prevention, risk evaluation of arsenic exposure as well as groundwater resource protection and management in an agriculture cultivated area.

本项目拟选取大同盆地为研究区，在对典型高砷地下水分布区水文地质结构与地下水水文地球化学过程精细刻画的基础上，针对农业活动导致的地下水硝酸盐面源输入，通过水文地球化学监测、土柱实验、静态批实验、地微生物学研究及水文地球化学模拟计算，揭示硝酸盐与砷并存的含水系统中其经历的各种物理、化学和生物过程及空间分布规律和时间上发生的先后顺序。在对比硝酸盐输入前后水化学序列及微生物种群多样性特征的基础上，分析硝酸盐输入对地下水系统中砷的活化与迁移富集的影响，揭示典型农耕区地下水系统中硝酸盐并存条件下砷迁移富集规律，丰富和发展对高砷地下水形成机理的认识。研究为农耕区高砷地下水防治、地下水砷污染风险评价及同类地区地下水资源保护与管理提供科学决策依据。

针对高砷地下水系统开展了地下水水化学监测、水文地球化学模拟及沉积物地球化学研究工作。通过研究发现地表灌溉导致的灌溉回水的垂向入渗补给对地下水水化学及水体砷含量具有重要影响。周期性灌溉导致的含水层氧化还原条件的变化可诱发Fe(III)-SO42-氧化还原循环，使得铁氧化物、铁硫化物及菱铁矿之间发生周期性的矿物相转变。上述矿物对砷具有不同的吸附及固定能力，因此，Fe(III)-SO42-氧化还原循环导致的矿物相变是控制监测场地地下中砷迁移富集的主要因素。灌溉活动导致的地表年轻有机质输入为微生物呼吸作用提供能量来源，进一步加剧了Fe(III)-SO42-氧化还原循环，进而影响地下水中砷的迁移转化。此外，地下水中存在的类醌类腐殖质为溶解性有机质、铁氧化物/硫酸盐及五价砷之间电子传递提供了重要通道，进而促进砷的还原与释放。研究的开展为全面揭示高砷地下水的成因提供了新的认识。