赣江中游浅层地下水水化学特征演化及成因分析

Evolution of groundwater hydrochemical characteristics and origin analysis in middle reaches of Ganjiang River

赣江是江西省主要水源,研究其地下水水化学特征及成因机理对流域水质保护至关重要。选取赣江中游吉安市井开区为研究区,于2019年丰-平-枯水期各采集研究区浅层地下水样45组,运用数理统计、Durov图、Gibbs图、离子比例系数、PHREEQC反向模拟等方法,研究了吉安市井开区浅层地下水的水化学分布特征和组成类型,讨论了其主控因素、主成分离子来源,并开展了典型径流路径水文地球化学模拟。结果表明:研究区浅层地下水属低矿化度淡水,主要阴阳离子为HCO_(3)^(-)、Ca^(2+),个别样本中NH_(4)^(+)、NO_(3)^(-)、SO_(4)^(2-)的异常值均与人类活动有关,水化学类型主要有HCO_(3)-Ca型、HCO_(3)-Ca·Mg型、HCO_(3)·SO_(4)-Ca型3种;研究区地下水化学形成的主控因素为岩石风化作用;离子比值关系表明水中组分主要源于碳酸盐岩矿物的溶解作用,其中Na^(+)、K^(+)主要源于盐岩的溶解,SO_(4)^(2-)源于少量蒸发岩矿物(石膏)的溶解,Ca^(2+)、Mg^(2+)源于方解石、白云石和硅酸盐矿物的溶解;水文地球化学反向模拟表明水流路径均发生白云石、石膏、岩盐的溶解作用,结合氯碱指数,地下水流存在一定的逆向阳离子交换作用。研究成果可为赣江中游地区地下水开发利用与保护提供理论依据。

Ganjiang River is the main water source of Jiangxi Province,studying its groundwater hydrochemical characteristics and genesis mechanism is crucial for the protection of the water quality in the basin.This study selected the Jingkai area of Ji′an City in the middle reaches of the Ganjiang River as the research area and collected 45 sets of shallow groundwater samples during the flood season,normal season,and dry season in 2019.Then,methods such as mathematical statistics,Durov diagrams,Gibbs diagrams,ion ratio coefficients,and PHREEQC reverse simulation were used to study the hydrochemical distribution characteristics and composition types of shallow groundwater in the region.The main controlling factors and ion sources of the main components were discussed,and hydrogeochemical simulations of typical runoff paths were carried out.The results showed that:the shallow groundwater in the study area belongs to low salinity freshwater,with the main anions and cations being HCO_(3)^(-)and Ca^(2+).The abnormal values of NH_(4)^(+),NO_(3)^(-),and SO_(4)^(2-)in some samples are related to human activities.The main chemical types of groundwater in the study area are HCO_(3)-Ca,HCO_(3)-Ca·Mg,and HCO_(3)·SO_(4)-Ca.The main controlling factor of the formation of groundwater chemistry in the study area is rock weathering.From the ion ratio relationship,it can be concluded that the main source of water components is the dissolution of carbonate minerals,among them,Na^(+)and K^(+)mainly come from the dissolution of salt rocks,SO_(4)^(2-)comes from the dissolution of a small amount of evaporite minerals(gypsum),Ca^(2+)and Mg^(2+)come from the dissolution of calcite,dolomite,and silicate minerals.The reverse simulation results of hydrogeochemistry indicated that the dissolution of dolomite,gypsum,and rock salt occurs along the water flow path.Combined with the chlor alkali index,there is a certain degree of reverse cation exchange in groundwater flow.The results can provide some theoretical basis for the development,utilization,and protection of groundwater in the middle reaches of the Ganjiang River.