Hydrogeochemistry And Influencing Factors In The Process Of Seawater Intrusion In Xiao Ling River Fan,Jinzhou City

Xiaoling river fan is located in the southwestern part of Jinzhou,near the Bohai Sea.The occurrence of seawater intrusion has destroyed groundwater resources and deteriorated water quality in the area.In order to clarify the current situation of seawater intrusion,and moreover,the chemical composition,formation and evolutionary laws of groundwater of this area.In August 2019,28 groundwater,9surface water,atmospheric precipitation and seawater samples were collected from Xiaoling river fan to offshore plain in Jinzhou city.Combined with field exploration sampling and indoor sample testing.The influence of seawater intrusion on the groundwater chemistry(hydrochemical composition characteristics,hydrochemical types,etc.)and hydrogen and oxygen isotopes(D and ¹⁸O)characteristics of the groundwater in the area is analyzed with more mature hydrochemical methods.The results show:(1)The distribution of seawater intrusion in the study area was judged according to the four indicators of chloride ion concentration,salinity,sodium adsorption ratio and salinity coefficient.The area north of Beiling village-Niangnianggongstreet-south of Laolongtou village-Xinglonggang-Beiergou-North of Qingtuozi village is a non-invasive area,and its south is a mild seawater intrusion area.Xishulin village and the eastern part of Ant Village are areas of severe seawater intrusion.Hetun village and Xiazhuangzi village are mainly areas with severe seawater intrusion.(2)The dominant cation in the fresh water of groundwater is Ca type,and there is no dominant anion.The dominant cation of brackish water is mainly Na type,and the anion is mainly Cl type.The type of groundwater has gradually changed from the HCO3-Ca·Mg type freshwater with low salinity in the piedmont to the Cl-Na type brackish water in the offshore plain area.There are differences in water chemistry types between the east and west sides of the fan to the front of the fan.(3)According to the Gibbs diagram and ion ratio analysis,the dissolved ions in groundwater are mainly affected by the action of water and rock,and the groundwater in offshore areas is affected by seawater mixing.The distribution characteristics of?D and?¹⁸O indicate that the groundwater sources in the study area include atmospheric precipitation recharge,surface water recharge,and groundwater lateral recharge.As the buried depth becomes shallower,it is more affected by evaporation.(4)The groundwater in the study area not only has the mixing effect under the influence of seawater intrusion,but also the mineral dissolution and precipitation and the alternate cation adsorption.Through reverse hydrogeochemical simulation,it is found that the saturation index of rock salt and gypsum in groundwater is less than 0,and both are in an unsaturated state;the saturation index of calcite and dolomite in some fresh water and most brackish water is greater than-0.5,which is basically saturated and supersaturated status.The saturation index of calcite and dolomite in a small number of freshwater samples located in the piedmont replenishment area is less than-0.5,which is not saturated.