Division Of Groundwater System And Hydrogeochemical Characteristics In Poyang Lake Basin

Poyang Lake Basin,located in the northern part of Jiangxi Province and on the south bank of the Yangtze River,is one of the key areas of the Yangtze River Economic Belt.In this paper,the groundwater system of Poyang Lake Basin is divided and the characteristics of each aquifer system are described based on the collected data and hydrogeological investigation.At the same time,the contour map method,Shukarev classification method,Piper three-line map,Gibbs graphical method,correlation analysis and ion ratio coefficient method are used to analyze the ion distribution characteristics,hydrochemical classification characteristics,groundwater chemical genesis and formation mechanism of the collected 153 groundwater samples in the study area.Based on the above research,the conclusions are as follows:(1)Based on groundwater hydrodynamic conditions,6 secondary groundwater flow systems including the Ganjiang secondary system and 14 tertiary groundwater systems including the Jinjiang-Ganjiang downstream tertiary system are divided.According to the geology,geomorphology,and characteristics of the aquifer medium,the Poyang Lake groundwater aquifer system is divided into seven aquifer sub-systems including the pore aquifer sub-system in the alluvial lake plain.(2)The contour map method is used to explore the distribution of TDS,total hardness,and main groundwater ions in different water-containing sub-systems in the study area.The results show that the groundwater in the study area is fresh water(TDS<1g/L),and 92.2%of the groundwater is soft water.The average TDS concentration and the Ca²⁺and HCO₃^-content are the highest in the water-bearing sub-system of carbonate fissured karst caves and in the groundwater respectively,and both are relatively high in the water-bearing sub-system of carbonate fissured karst caves and the general clastic rock-like fissured pore water.The high content of NO₃^-and F^-in groundwater in some areas indicates that the area is seriously affected by agricultural production activities and fluorite mine pollution.(3)The Shukalev classification and Piper three-line diagram were used to study the groundwater hydrochemical types of each aquifer sub-system.The results show that the HCO₃-Na+Ca water type,HCO₃-Ca water type and HCO₃-Ca+Mg water type are the main groundwater hydrochemical types in the study area.Among them,the pore water-bearing sub-system of the alluvial lacustrine plain and the alluvial plain as well as the mountain magmatic rock-like fissured water-bearing sub-system are mainly HCO₃-Na+Ca water type;the carbonate carbonate-like fissure karst cave water-bearing sub-systems,and mountains hills are generally The clastic rock-like pore water sub-system and hilly red-bed fissure pore water-based sub system are mainly HCO₃-Ca type water;the mountain and hill metamorphic rock-like fissure water sub system is mainly based on HCO₃-Ca+Mg type water.(4)The analysis has used the Gibbs graphic method,correlation analysis method,and ionic ratio coefficient method.The results show that the chemical genesis of groundwater in the study area is mainly affected by the action of rock wind.The genesis of each water bearing sub-system is related to the dissolution of carbonate rocks and aluminosilicate minerals,and there are cation exchange and water flow alternation.Among them,the pore water subsystem of the alluvial lacustrine plain and the alluvial plain are also affected by the dissolution of sulfate rocks such as mirabilite and gypsum and agricultural production;water flow alternating and the cation exchange of the carbonate sub-fracture karst cave water sub-system and the mountain magmatic rock-like fissured water-bearing sub-system are relatively strong;mountain magmatic rock fissured aquifer sub-system are greatly affected by magmatic weathering,and the alternation of water flow is also strong.