塔里木盆地南缘绿洲带地下水砷氟碘分布及共富集成因

Distribution and co-enrichment genesis of arsenic,fluorine and iodine in groundwater of the oasis belt in the southern margin of Tarim Basin

由于地表水资源稀缺,地下水是塔里木盆地南缘绿洲带重要用水水源,因此,系统查明该区地下水砷氟碘的分布及成因至关重要。基于塔里木盆地南缘绿洲带233组地下水水样检测结果,分析不同含水层中高砷、高氟和高碘地下水的空间分布及水化学特征,结合研究区地质、水文地质条件和地下水赋存环境进一步揭示影响地下水砷氟碘的来源、迁移与富集的水文地球化学过程。结果表明:地下水砷、氟、碘浓度变化范围分别为1.0~91.2μg/L、0.01~28.31 mg/L、10.0~2637.0μg/L。地下水高砷、高氟和高碘水样分别占总水样的7.3%、47.2%和11.6%,砷氟碘共富集占比为3.0%。砷氟碘共富集地下水主要分布于研究区中部的民丰县,水化学类型主要为Cl·SO_(4)-Na型。自补给区至过渡区再至蒸发区,地下水氟、碘浓度明显增大,砷浓度在过渡区和蒸发区均较大;砷氟碘共富集地下水取样点主要分布于36.0~60.0 m深度的浅层承压含水层中。浅层地下水受蒸发作用和矿物溶解沉淀作用的影响,随砷氟碘富集项的增多而增大。第四纪成因类型中风积物对氟浓度的影响较大,洪积湖积物对砷和碘浓度的影响较大。细粒岩性、平缓的地形、地下水浅埋条件、偏碱性的地下水环境、微生物降解作用下有机质介导的矿物溶解是利于砷氟碘共富集的主要机制。

Owing to the scarcity of surface water resources,groundwater is an important water source in the oasis belt of the southern margin of Tarim Basin.Thus,it is very important to systematically identify the distribution and origin of arsenic,fluorine,and iodine in groundwater in this area.Based on the detection results of 233 groups of groundwater samples from the oasis belt of the southern margin of Tarim Basin,the spatial distribution and hydrochemical characteristics of groundwater with high arsenic,high fluorine,and high iodine in different aquifers were analyzed,and the hydrogeochemical processes that affected the source,migration,and enrichment of arsenic,fluorine,and iodine in groundwater were further revealed by combining the geological and hydrogeological conditions with the groundwater occurrence environment in the study area.The levels of arsenic,fluorine,and iodine in groundwater were found to vary from 1.0-91.2μg/L,0.01-28.31 mg/L,and 10.0-2637.0μg/L,respectively.Groundwater samples with high arsenic,high fluorine,and high iodine accounted for 7.3%,47.2%,and 11.6%of the total water samples,respectively,and arsenic,fluorine,and iodine co-enrichment accounted for 3.0%.Arsenic,fluorine,and iodine co-enriched groundwater was found to be mainly distributed in Minfeng County in the middle of the study area,and the Cl·SO_(4)-Na type was identified as the main hydrochemical type.Groundwater fluorine and iodine levels significantly increased from the recharge zone to the transition zone and then to the evaporation zone.Further,arsenic levels were greater in both the transition and evaporation zones.The sampling points for arsenic,fluorine,and iodine co-enrichment in groundwater were mainly distributed in the shallow confined aquifer of 36-60 m.Shallow groundwater was affected by evaporation and mineral dissolution and precipitation,which increased with an increase in the arsenic,fluorine,and iodine enrichment terms.Quaternary aeolian deposit had a remarkable influence on fluorine content,while pluvial-lacustrine deposit had a great influence on arsenic and iodine content.Altogether,fine-grained lithology,gentle terrain,shallow burial conditions of groundwater,slightly alkaline groundwater environment,and mineral dissolution mediated by organic matter under microbial degradation were the main mechanisms conducive to arsenic,fluorine,and iodine co-enrichment.