崇明岛浅层地下水化学特征及其影响机制

Hydrochemical Characteristics and Impact Mechanism of Shallow Groundwater in Chongming Island,China

为探究长江口浅层地下水化学特征及其影响机制,选择崇明岛为研究对象,采集22个浅层地下水样本和3个地表水样本,检测11项水化学指标及氢氧同位素.利用描述性统计分析、Arc GIS空间分析、Piper图解和离子比例系数等分析方法,分析研究区浅层地下水化学类型与离子空间分布,讨论控制浅层地下水化学演化过程的主要因素和离子来源,探究地表水与浅层地下水的水力联系.结果表明:崇明岛浅层地下水pH在7.30~7.94之间,整体呈中性硬水,36%为极硬水,围垦地区浅层地下水矿化程度较高;浅层地下水化学类型有13种,以HCO_(3)-Ca水为主,占样本数的27%,主要分布在崇明岛中部、西南部;从西部到东部阴离子由HCO_(3)-向Cl-过渡,阳离子由Ca^(2+)向Na^(+)过渡,在围垦区,浅层地下水化学类型以Cl·HCO_(3)-Na为主.研究显示,水-岩作用、阳离子交换作用和人类活动是影响崇明岛浅层地下水化学特征的主要影响因素,浅层地下水与地表水水力联系紧密.

In order to investigate the hydrochemical characteristics and impact mechanism of shallow groundwater in the Yangtze River Estuary,22 shallow groundwater samples and 3 surface water samples on Chongming Island were collected and tested for 11 water chemical indicators as well as hydrogen and oxygen isotopes.With the combination of methods such as descriptive statistical analysis,Arc GIS spatial analysis,Piper diagram and ion proportionality coefficient determination,the hydrochemical types and ion spatial distribution in the study area were determined.Furthermore,the main factors and ion sources controlling the chemical evolution of the groundwater were discussed.The results show that the pH of shallow groundwater in Chongming Island is between 7.30 and 7.94,representing neutral hard water,and 36%of the groundwater is extremely hard water.The degree of groundwater mineralization in the reclamation area is relatively high.The groundwater hydrochemistry is relatively complex in the study area,including 13 types.The major type is HCO_(3)-Ca water,accounting for 27%of water samples,and is mainly distributed in the middle and southwest area of Chongming Island.From the west to the east,the anions transition from HCO_(3)-to Cl-,and the cations transition from Ca^(2+)to Na^(+).In the reclamation area,the groundwater chemical is mainly Cl·HCO_(3)-Na.Therefore,water-rock interaction,cation exchange process and human activities are the main factors affecting the chemical characteristics of shallow groundwater in Chongming Island.There is a hydraulic connection between surface water and groundwater,and recharge of water in the area mainly originates from atmospheric precipitation.