莱州湾南岸平原地下水化学特征研究

用2009年莱州湾南岸地下水最新监测数据,将研究区地下水淡水区、微咸水区、咸盐水区和卤水区进行经典统计分析、相关分析、等值线图和Piper三线图绘制,阐述了水化学类型和成分特征从南往北的变化:EC、TDS、Na+、K+、Mg2+、Cl-、SO42-的平均浓度从南部淡水到北部卤水呈现逐渐增大趋势,因为在卤水区普遍发生碳酸钙沉淀,Ca2+和HCO3-则在咸盐水区浓度达最高;pH值从淡水到卤水呈现从弱碱性到弱酸性的转变;从淡水区向卤水区地下水化学组分阴离子由HCO3-为主变为Cl-为主,阳离子由Ca2+为主变为Na+为主;此外河流对地下水起到淡化和冲刷的作用。主成分分析法提取了水化学3个主成分,分别代表了地下水盐化指标、生物化学作用和碳酸钙沉淀。进一步结合系数比值法和饱和指数计算,在对本区水文、地质以及离子水文地球化学特性分析基础上,指出地下卤水阴阳离子中占绝对优势的Cl-、SO42-、Na+、Mg2+的毫克当量百分数与正常海水的值非常相近而与地下淡水的值相差甚远,反映出本区地下卤水起源于古海水,为沉积海水。此外卤水绝非海水简单浓缩的产物,其间还包括复杂的水化学变质过程及后期演化如矿物沉淀、阳离子交换(K+-Ca2+;Na+-Ca2)+、去白云岩化作用和硅酸盐蚀变等。饱和指数的计算表明石膏在卤水矿化度达100 g/L之后才开始缓慢沉淀,而文石、方解石和白云石基本一直处于饱和沉淀状态,且文石和方解石的饱和指数散点分布极为相似,说明两者可能同时发生沉淀。

Study on the groundwater hydrochemical characteristics in the southern Laizhou Bay

According to TDS(total dissolved solutes),groundwater in the southern Laizhou Bay was classified to fresh water,brackish water,saline water and brine.Classical statistical analysis,correlation analysis,contour map and Piper Diagram drawing were conducted.Changes of water types and chemical compositions were described from south to north.Parameters including EC(electrical conductivity)、TDS、Na+、K+、Mg2+、Cl-and SO42-represented an ascending trend in the order of freshwater,brackish water,saline water and brine.From freshwater to brine,pH value showed a gradual change from Alkalescence to faint acid accordingly.And major chemical compositions transfered from anion HCO3-to Cl-and cation from Ca2+ to Na+.The concentration of Ca2+ and HCO3-reached the highest concentration in saline water due to carbonate precipitation widely occurring in the brine zone.Three principal components were extracted,representing groundwater salinity indicators,biochemical function,and calcium carbonate precipitation by PCA(principle component analysis).On the basis of local hydrological,geological and ion hydrogeochemical characteriistics analysis,incorporating coefficient ratio and saturation index(SI) calculation,it′s indicated that brine and seawater had basically the same chemical composition,reflecting brine originating from ancient seawater,and furthermore brine was definitely not a simple product of seawater concentration.In the complex process of deterioration of water chemistry took place the cationexchange(K+-Ca2+;Na+-Ca2+),dedolomitization and silicate alteration and the like.SI calculation denoted that gypsum began to precipitate after brine salinity reached 100 g·L-1,while aragonite,calcite and dolomite has been in a saturated state in brine.And aragonite and calcite may precipitate simultaneously.