兰州不同城镇功能区地下水氟赋存特征及影响因素

Characteristics and driving factors of fluoride in groundwater in different urban functional area of Lanzhou city

高氟地下水对生态环境及人类健康存在潜在威胁。城镇化地区受地质背景与人类活动双重影响,地下水中氟的来源及其分布较为复杂,探讨地下水中氟的赋存特征对于保障地下水供水安全具有重要意义。以西北干旱区最大的工业城市兰州为例,采用数理统计、离子比、饱和指数分析等方法,研究了兰州不同城镇功能区高氟地下水的赋存环境特征及主要水文地球化学过程,阐明了人为活动对氟化物迁移富集的影响。结果表明:(1)研究区地下水中F-的质量浓度介于0~4.8mg/L之间,超出地下水质量Ⅲ类标准(1.0mg/L)的高氟水共计13组,超标率为20.3%。(2)受人类活动强度与不同人为源输入影响,不同城镇功能区地下水中氟的赋存特征差异明显,其中西固工业区地下水中氟含量最高,高氟地下水样品占47.4%;城关老城区和断陷盆地新城区地下水中的氟含量相对较低,高氟地下水占比依次为7.1%和9.7%。(3)研究区高氟地下水以SO_(4)•Cl—Na和Cl•SO_(4)—Na型水为主,表现出贫钙富钠弱碱性特点。(4)含氟矿物的溶解、方解石与白云石的沉淀/溶解、黏土矿物表面钙与钠之间的阳离子交换、强烈的蒸发浓缩作用和盐效应是导致研究区地下水中氟化物富集的主要水文地球化学过程。研究表明城镇化、工业化导致天然高氟水进一步劣变恶化,工业废水的泄漏是西固工业区地下水氟浓度升高的重要驱动力。结果可为高氟背景区人为干扰下的氟化物迁移富集研究提供借鉴。

High-fluorine groundwater is a potential threat to ecological environment and human health.The source and distribution of fluoride in groundwater in urbanized areas are complicated due to the double influence of geological background and human activities.It is of great significance to identify the characteristics of fluorine in groundwater to ensure the safety of groundwater.This study analyzed the environmental characteristics and main hydrogeochemical processes of high-fluorine groundwater in different urban functional areas of Lanzhou city,the largest industrial city in the arid region of Northwest China,based on the mathematical statistics,ion ratios and saturation index analysis.Then the influence of human activities on the migration and enrichment of fluoride was revealed.The results show that theρ(F-)in the groundwater in the study area ranges from 0 to 4.8 mg/L,and 13 high-fluoride water samples exceeded the standard of groundwater quality Class III(1.0 mg/L),with an excess rate of 20.3%.Under the influence of intensity of human activity and sources of human input,the distribution characteristics of fluorine in groundwater in different urban functional areas are prominently different.The fluorine content of groundwater in the Xigu Petrochemical Industrial Zone is the highest,with the 47.4%of high-fluorine groundwater.While in commercial residential areas and new urban areas the fluorine content is relatively low,with the 7.1%and 9.7%of high-fluorine groundwater,respectively.The high-fluorine groundwater in the study area is mainly SO_(4)•Cl—Na and Cl•SO_(4)—Na type water,which is low in calcium,rich in sodium and weak in alkalinity.The dissolution of fluorinated minerals,precipitation/dissolution of calcite and dolomite,cation exchange between calcium and sodium on the surface of clay minerals,strong evaporation and salt effect are the main hydrogeochemical processes of fluoride enrichment in groundwater in the study area.Urbanization and industrialization lead to the further deterioration of natural high fluorine water,the industrial wastewater leakage from petrochemical leads to the further dissolution of fluoride in the formation,which is an important driving force for the enrichment of high fluorine groundwater in the Xigu Industrial Zone.The study provides basic information for the fluoride migration and enrichment in the high fluoride background area with human activities.