岩溶区典型工业型城市地下水水化学特征及成因机制

文章以广西柳州市岩溶地下水为研究对象，在岩溶水文地质调查和样品采集测试的基础上，采用数理统计法、水化学方法（Piper图、Gibbs图、离子比值系数，矿物饱和指数计算）、因子分析法和模糊综合评价法，分析工业型城市岩溶地下水水化学特征及形成机制，开展岩溶地下水质量评价。结果表明，研究区岩溶地下水为中-弱碱性水，Ca2+、Mg2+、HCO₃?、SO₄2?是主要的阴阳离子，水化学类型以HCO₃-Ca型和HCO₃-Ca·Mg型为主，且城区的SO₄2?型水的比例远高于非城区。区内岩溶地下水水化学组分及演化主要受水－岩作用、工业污染、城镇生活污染和农业活动等主控因素的影响，贡献率分别为31.52%、25.15%、18.12%和10.74%。其中，城区的水化学组分受人类活动的影响程度大于非城区的。矿物饱和指数表明，区内方解石和绝大多数白云石为饱和状态，而石膏和盐岩均为溶解状态。不同功能区的水化学敏感指标有差异，工业区以重金属为主，农业区以三氮为主，生活区以K+、Na+、Cl?、SO₄2?为主。研究区整体水质较好，Ⅰ－Ⅲ类水的比例高达约87.39%；但不同区域的水质差异较大，其中城区的水质较差，超标因子主要为Al、Mn、Pb、Fe、Hg；非城区的水质较好，超标因子主要为三氮。研究成果可以为工业型城市岩溶地下水污染防治提供科学依据。 

Hydrochemical characteristics and water quality evaluation of karst groundwater in typical industrial cities

As economic pillars of the karst area in south China, industrial cities located in this area play an important role in the promotion of national strategy and economic development. Karst groundwater, the main water source of industrial cities in the karst area, is vital for urban development. Therefore, studies on hydrochemical characteristics of karst groundwater and solutions to water pollution problems have always been working focuses of local governments, but little attention to the chemical problems of karst groundwater in industrial cities has been paid in previous studies. This study takes karst groundwater in Liuzhou City, Guangxi as the research object. Based on karst hydrogeological survey, a total of 119 groups of karst underground water samples were collected, including 31 groups of urban underground water samples and 88 groups of non-urban underground water samples. Using mathematical statistics, hydrochemistry method (Piper diagram, Gibbs diagram, ion ratio coefficient, mineral saturation index calculation), factor analysis and fuzzy comprehensive evaluation method, we analyzed the hydrochemical characteristics and formation mechanism of karst groundwater in industrial cities, and carried out the quality evaluation of karst groundwater. Results show that karst groundwater in the study area is generally medium-weak alkaline water with a small amount of acidic water. The main cations are Ca2+ and Mg2+, and the main anions are HCO₃- and SO₄2-. In terms of concentration and variation degree, karst groundwater in urban areas is larger than that in non-urban areas. In terms of water chemistry types, there are also obvious differences between the two kinds of areas, that is, water chemistry types in urban areas are mainly HCO₃-Ca+Mg type, while those in non-urban areas are mainly HCO₃-Ca type. The proportion of SO₄2- type water in urban areas is much higher than that in non-urban areas, reflecting that urban areas suffer serious pollution from more pollution sources than non-urban areas. The chemical composition of groundwater in the study area is mainly controlled by rock dissolution, industrial pollution, urban pollution and agricultural activities, with contribution rates of 31.52%, 25.15%, 18.12% and 10.74%, respectively. Dissolution factors of rock are mainly carbonate minerals such as calcite and dolomite, primarily from dolomite dissolution in urban areas and calcite dissolution in non-urban areas. The dissolution factors are mainly distributed in Liujiang district and northwestern Luzhai county of Liuzhou City. Industrial pollution factors are mainly distributed in Liunan district, Liubei district and other areas of Liuzhou City. The industrial pollution in these areas is related to the discharge of wastewater, waste gas and waste residue by a number of heavy industry enterprises, leading to the excessive concentration of heavy metals. Urban living pollution factors are mainly distributed in Chengzhong district, Yufeng district, Luzhai county, Liucheng county and other areas, and are related to domestic sewage discharge and domestic garbage leaching. The factors of agricultural activities are mainly distributed in Liujiang river, Luoqing river, Longjiang river and other river valleys, and are related to the use of chemical fertilizers and pesticides in agricultural activities and the direct discharge of animal feces from breeding. Hydrochemical sensitivity indexes of different functional areas are diverse, among which the industrial area is dominated by heavy metals, agricultural area by trinitrogen, and living area by K+, Na+, Cl- and SO₄2-. Mineral saturation indexes show that calcite and most dolomite are saturated, while gypsum and salt rocks are dissolved. The karst groundwater quality is good as a whole, mainly I-III water, accounting for 86.29%, but the water quality varies greatly in different areas. The water quality in the urban area is poor, with the proportion of IV-V water as high as 35.48%. The places with water exceeding permitted levels are mainly distributed in Liunan district and Liubei district of Liuzhou City, and factors exceeding levels are Al, Mn, Pb, Fe and Hg. Reasons for exceeding levels are related to the discharge of "three types of waste" and geochemical background of heavy industry enterprises. The water quality in non-urban areas is better, and the proportion of IV-V water is only 6.45%. The places with water quality exceeding permitted are only distributed in Liujiang river valley and Luoqing river valley, and the factor exceeding levels is trinitrogen, which is caused by the excessive use of chemical fertilizers and pesticides.