陕北靖边高铬地下水中硝酸根分布及来源  

Distribution and source of nitrate in high-chromium groundwater in Jingbian,northern Shaanxi

作　　者：郭华明[1,2] 尹嘉鸿 严松 刘超[2] GUO Huaming;YIN Jiahong;YAN Song;LIU Chao(MOE Key Laboratory of Groundwater Circulation and Environmental Evolution,China University of Geosciences(Beijing),Beijing 100083,China;School of Water Resources and Environment,China University of Geosciences(Beijing),Beijing 100083,China)

机构地区：[1]中国地质大学(北京)地下水循环与环境演化教育部重点实验室,北京100083 [2]中国地质大学(北京)水资源与环境学院,北京100083

出　　处：《地学前缘》2024年第1期384-399,共16页Earth Science Frontiers

基　　金：国家自然科学基金项目(42130509)。

摘　　要：天然高铬地下水通常含有较高浓度的硝酸根,然而高铬地下水中硝酸根来源及其联系却并不清楚。本文以陕北黄土高原靖边西南地区的高铬地下水为研究对象,采集了不同深度的地下水和沉积物样品,并测试了地下水样品中的溶解Cr、主要阴阳离子、δ^(18)O、δD、δ^(18)O-NO_(3)、δ^(15)N-NO_(3)等以及沉积物的主要组分和可溶性组分。研究结果表明,研究区地下水的水化学组分主要受水文地质条件的影响。第四系黄土潜水水化学类型主要为HCO_(3)-Na型和HCO_(3)-Ca-Mg型;白垩系环河组、洛河组砂岩承压水水化学类型复杂,主要为HCO_(3)-SO_(4)-Cl-Na-Mg型、HCO_(3)-SO_(4)-Na-Mg型、SO_(4)-Cl-Na-Mg型,地下水处于偏碱性、氧化的环境,具有较高的可溶盐含量。潜水的水化学组分主要来自含水层中硅酸盐风化;承压水水化学组分主要来源于蒸发盐的溶解。垂向上,承压水中硝酸根的平均浓度高于潜水和地表水;地下水硝酸根浓度超标率在研究区从东北到西南呈现高-低-高的趋势;沉积物中可溶性硝酸根与地下水样品在深度上具有相似的变化规律,表明地下水硝酸根主要来源于沉积物。δ^(18)O-NO_(3)和δ^(15)N-NO_(3)结果表明,硝化反应是研究区氮素循环转化的主要过程。在偏碱性氧化性地下水环境中,受溶解氧、硝酸根和硝化反应等多种因素的共同作用,铬趋于从岩石中氧化溶解,迁移进入地下水中。Natural high-chromium(Cr)groundwater usually contains high concentration of nitrate,but the source of nitrate and its relationship to Cr enrichment are unclear.In this study,water and sediment samples were collected at different depths from the high-Cr region of southwestern Jingbian,Loess Plateau,northern Shaanxi,and the dissolved Cr,soluble ionic species,δ^(18)O,δD,δ^(18)O-NO_(3),δ^(15)N-NO_(3),and main and soluble sediment components were analyzed.Unconfined groundwater from Quaternary loess aquifers was mainly of HCO_(3)-Na and HCO_(3)-Ca-Mg types.Confined groundwater from sandstone aquifers of the Cretaceous Huanhe-Luohe Formations was of complex hydrochemical types,mainly HCO_(3)-SO_(4)-Cl-Na-Mg,HCO_(3)-SO_(4)-Na-Mg and SO_(4)-Cl-Na-Mg types.The groundwater environments were weakly alkaline and oxic,with high concentrations of dissolved salts.The hydrochemical components of unconfined groundwater mainly derived from silicate weathering,while dissolution of evaporites mainly controlled the chemistry of confined groundwater.The average concentration of nitrate in confined groundwater was higher compared to unconfined groundwater and surface water.Spatial distribution of nitrate concentrations in groundwater showed a high-low-high trend from northeast to southwest in the study area.Nitrate contents in sediment and groundwater samples had similar variation trends with depth,indicating that nitrate in groundwater mainly originated from aquifer sediments.δ^(18)O-NO_(3)andδ^(15)N-NO_(3)values indicated that nitrification was the main process of nitrogen cycling and transformation in groundwater systems.Under alkaline,oxic groundwater environments,the presence of dissolved oxygen,nitrate,and nitrification was conducive to chromium oxidation in aquifer solids and release of Cr(VI)into groundwater.

关 键 词：地下水 硝酸根 六价铬 水文地球化学 氮氧同位素 

分 类 号：P641.11[天文地球—地质矿产勘探] P641.3[天文地球—地质学]