合浦盆地西部地区地下水水化学特征及形成机制

Hydrochemical Characteristics and Formation Mechanism of Groundwater in the Western Region of Hepu Basin,Beihai City

北海市是地下水支撑社会经济发展的典型滨海城市,研究该区水化学特征及形成机制,对服务水资源科学管理和海岸带生态环境保护具有重要意义.通过北海市合浦盆地西部地区地下水调查、水样采集与分析,综合运用水化学和同位素理论和方法揭示了控制地下水水质的主要水文地球化学过程.结果表明,地下水具有低pH值和低矿化度的显著特征.孔隙水水化学类型以硝酸型水为主,Na^(+)和Cl^(-)浓度沿径流方向明显增加;裂隙水以Ca-HCO_(3)、Ca-Cl·HCO_(3)、Ca·Na-HCO_(3)和Na-Cl·HCO_(3)型为主.地下水受大气降水补给,水文地球化学过程主要受到水岩相互作用、阳离子交换作用和人类活动的综合影响.Na+、K^(+)和Cl^(-)主要来源于蒸发盐岩和硅酸盐岩,Ca^(2+)、Mg^(2+)、HCO_(3)^(-)和SO_(4)^(2-)主要来自碳酸盐岩和蒸发盐岩矿物的溶解,NO_(3)-主要来源于人类活动.建议在硝酸型水出现的区域及时进行地下水污染防治,避免水质进一步恶化.

Beihai City is a typical coastal city where groundwater provides a strong support for social and economic development.Studies on the hydrochemical characteristics and formation mechanism in Beihai City play an important role in the scientific management of water resources and coastal ecological environment protection.In this study,we revealed the main hydrogeochemical processes controlling groundwater quality by means of groundwater survey and water sample collection in the western region of Hepu Basin,Beihai City,combined with hydrochemistry and isotope theories and methods.The results showed that groundwater had the remarkable features of low pH value and low mineralization degree.For pore water,hydrochemistry type by primarily NO_(3) type water and concentrations of Na^(+)and Cl-were modestly increased along the flow path.Ca-HCO_(3),Ca-Cl·HCO_(3),Ca·Na-HCO_(3),and Na-Cl·HCO_(3) types were predominant in fissure water.The groundwater was of meteoric origin,hydrogeochemical evolutions were mainly affected by water-rock interactions,cation exchange,and anthropogenic activities.Na^(+),K^(+),and Cl^(-)were mainly derived from evaporite and silicate rocks;Ca^(2+),Mg^(2+),HCO_(3)-,and SO_(4)^(2-)were from carbonatite and evaporite;and NO_(3)-principally arose from anthropogenic activities.This study suggests that the groundwater pollution prevention and control should be carried out as soon as possible in the area where the NO_(3) type water occurs to avoid the further deterioration of water quality.