苏北沿海地区潜水水化学特征及形成机理

Chemical Characteristics and Formation Mechanism of Phreatic Water in Coastal Area of Northern Jiangsu

为给苏北沿海地区潜水水质保护措施的制定提供理论依据,对该地区潜水水化学特征及形成机理进行研究。依据研究区2015年潜水取样深度小于20 m的281个采样点的水化学数据,结合研究区水文地质条件,采用Gibbs图、离子比例系数法、氯碱指数及主成分分析法等,对研究区潜水水化学形成机理进行了分析。结果表明:随潜水径流方向,潜水TDS(溶解性总固体)及水化学类型呈良好的水平分带规律,即补给区水化学类型主要为HCO_(3)-Ca(·Mg·Na)或HCO_(3)·Cl-Na·Ca(Mg)型,径流区主要为HCO_(3)·Cl-Na·Ca型或Na·Mg型,排泄区为Cl·HCO_(3)-Na(·Mg)或Cl-Na型,且在径流过程中ρ(TDS)也逐渐增大;潜水水化学特征主要受岩石风化作用控制,随潜水流向,蒸发浓缩作用逐渐增强,阳离子交替吸附作用逐渐代替溶滤作用,在排泄区变为以阳离子交换、蒸发浓缩和混合作用为主,其中混合作用对滨海地区的影响最大;潜水水化学特征还受到人类活动的影响。

In order to provide a theoretical basis for the formulation of phreatic water quality protection measures in the coastal area of northern Jiangsu,the chemical characteristics and formation mechanism of phreatic water in the area were studied.This research is based on a total of 281 sets of water chemistry data from the sampling sites with a phreatic water depth less than 20 meters in the study area in 2015 combined with the hydrogeological conditions.Gibbs diagram,ion ratio coefficient method,chlor alkali index and principal component analysis method were used to analyze the formation mechanism of phreatic water chemistry in the study area.The results show that along with the direction of phreatic runoff,the TDS(total dissovled solids)and hydrochemical types show good horizontal zonation,the hydrochemical type of recharge area is mainly HCO_(3)-Ca(·Mg·Na)or HCO_(3)·Cl-Na·Ca(·Mg),the subsurface runoff area is mainly HCO_(3)·Cl-Na·Ca or Na·Mg,and the discharge area is mainly Cl·HCO_(3)-Na(·Mg)or Cl-Na.TDS also gradually increased form recharge area to discharge area.The chemical characteristics of phreatic water are affected by rock weathering.With the flow direction of phreatic water,the effect of evaporation and concentration is gradually increased,and the leaching is gradually replaced by alternate cation adsorption.In the discharge area,cation exchange,evaporation concentration and mixing are the main processes,and mixing has the greatest impact on the coastal area.The chemical characteristics of phreatic water are also affected by human activities.