大同盆地地下水高砷、氟、碘分布规律与成因分析及质量区划

为了对大同盆地地下水中砷、氟、碘等的分布和成因进行分析,开展地下水质量区划,依据地下水污染调查取得的最新系列测试数据,结合以往水文地质和水文地球化学研究成果,编制大同盆地浅层和中深层地下水砷含量、氟含量、碘含量等水化学特征分布图,以直观反映大同盆地地下水高砷、高氟、高碘区的空间分布规律; 通过分析pH值、硫酸根含量、硝酸根含量、铁含量、锰含量与砷的关系,探讨高砷水的形成原因; 根据pH值、钙离子、重碳酸氢根离子与氟的关系,分析氟超标原因; 指出高碘区与高氟区分布的相似性和成因的相似性。研究结果表明,盆地周边高砷、高氟岩层是地下水砷、氟的原生来源,特定的河湖相沉积环境则为砷、碘的富集提供了原生地质条件; 北部地区氟增高与地下水位下降致使黏性土中的氟离子进入含水层有关,中部地区高氟与土壤盐渍化有关; 中部富含淤泥质黏土的湖相地层是碘富集的原生地质因素,冲积洼地地下水径流条件滞缓是碘富集的水动力因素; 干旱气候条件下强烈的蒸发浓缩作用亦是高氟、高碘地下水形成的重要因素。依据砷、氟、碘、硝酸盐、亚硝酸盐、总含盐量(total dissolved salt,TDS)、总硬度、氨氮等单组分含量分布,利用GIS空间分析功能,进行了大同盆地浅层和中深层地下水质量区划,可为当地地下水开发利用提供地学依据。

Distribution regularity,origin and quality division of high arsenic,fluorine and iodine contents in groundwater in Datong Basin

In order to analyze the distribution and origin of arsenic, fluorine and iodine in groundwater in Datong Basin, groundwater quality zoning was classified. According to the latest series of test data of groundwater pollution, and the previous research of hydrogeology and hydrogeochemistry, the distribution of water chemical characteristic were compiled, including the contents of arsenic, fluorine and iodine in groundwater of Datong Basin, to reflect the spatial distribution regularity of high arsenic, fluorine and iodine contents groundwater in Datong Basin directly. The reasons for the formation of the high arsenic water were discussed through analyzing the relationships between pH, sulphate, nitrate, iron, manganese contents and arsenic contents. According to the relationships between pH, calcium ion, bicarbonate ion and fluorine, the causes of excessive fluorine were analyzed, and the similarity of distribution and origin of iodine and fluorine area was pointed out. The study results show that the surrounding strata with high arsenic and fluorine contents are the primary sources of arsenic and fluorine in groundwater. The specific lacustrine sedimentary environment provides the primary geological conditions for the enrichment of arsenic and iodine. The increase of fluorine in the northern part of Datong Basin is related to the moving of fluoride ion from the cohesive soil to the aquifer, because of the drop of underground water level. The high fluoride contents in the central region is related to the soil salinization. The lacustrine strata in the central region with rich salty clay is the primary geological factor of iodine enrichment, and the stagnant conditions of groundwater flow in alluvial depression area is the hydrodynamic factor of iodine enrichment. The intense evaporation and concentration under the dry climate conditions is con important factor for forming high fluorine and iodine contents groundwater. Based on the content distribution of the single component such as arsenic, fluorine, iodine, nitrate, nitrite, TDS, total hardness, ammonia nitrogen and so on, the authors carried out the quality division of the shallow and the middle and deep groundwater in Datong Basin by using the spatial analysis function of GIS. This paper would provide the geological basis for the development and utilization of the local groundwater.