Study On Chemical Characteristics And Genesis Mechanism Of Groundwater In Hongjiannao Basin

Hongjiannao is an important inland lake in China.In recent years,the area and water level of Hongjiannao lake have been continuously decreasing,and the water pollution of Hongjiannao lake has become increasingly serious.As one of the main recharge sources of Hongjiannao,the variation of groundwater volume and quality directly affects the hydrochemical characteristics of lake water.In this study,the groundwater in Hongjianao basin was studied by using mathematical statistics,Piper ternary diagram,Shukalev classification,Gibbs diagram,correlation analysis,mineral saturation index,ion ratio and isomap to analyze its spatial distribution characteristics,evolution and formation mechanism.PHREEQC software is used to simulate mineral dissolution-precipitation equilibrium and other hydrochemical processes in groundwater system.The main conclusions are as follows:（1）The p H range of groundwater in the study area is 7.75-8.92;TDS range was205.85-1201.60 mg/L;Ca²⁺and HCO₃^-were the dominant anion and cation,respectivly.The mass concentration of main ions（mg/L）was ranked as cation:Ca²⁺>Na⁺>Mg²⁺>K⁺,and anion:HCO₃^->SO₄^2->Cl^->NO₃^-.（2）The chemical components of groundwater in Hongjiannao Basin are affected by weathering dissolution,cation exchange,evaporation and concentration of carbonate rocks（calcite and dolomite）,silicate minerals（albite,calcium feldspar and potassium feldspar）,fluorite,gypsum and rock salt,and human activities.Among them,Na⁺mainly comes from the dissolution and cation exchange of salt rock and silicoaluminate;Ca²⁺and Mg²⁺mainly come from the weathering and reverse cation exchange of silicate and carbonate minerals;Cl^-mainly comes from salt rock dissolution;SO₄^2-mainly comes from gypsum dissolution;HCO₃^-mainly comes from the dissolution and desulfuration of carbonate rocks.（3）The content of NO₃^-in groundwater in the study area exceeds the three groundwater quality standards（20 mg/L）,which is the main pollutant of groundwater in the study area.It mainly comes from fertilization,domestic sewage discharge and human and animal feces.Human activities are the main factors affecting the water quality indicators and the uneven spatial distribution of ions.The construction of reservoirs,agricultural and animal husbandry activities and urbanization will promote the enrichment of some ions,and affect the content,spatial distribution and evolution of chemical components in regional groundwater environment.（4）In the recharge area of the basin,the hydraulic gradient is large,the groundwater flow rate is fast,the contact time with the aquifer medium is short,and the reaction is insufficient.The water-rock interaction intensity is less than that of the runoff area and the discharge area.The western area of the basin is large and the groundwater runoff path is long.The water-rock interaction intensity is greater than that in the eastern region.Strong cation exchange reaction occurred in the basin.