Hydrochemical Characteristics Of Groundwater In Shandong Coast Under The Influence Of Seawater Intrusion

The coastal zone is the area where most frequent marine activities of human occur but the ecosystem is extremely vulnerable.This paper takes the coastal zone of Shandong coastal cities as the study area,based on field water sample collection and water chemistry experiments,and uses mathematical statistics to assess the regional groundwater water chemistry characteristics and water quality on the basis of hydrogeochemical analyses for Shandong coastal cities,with the help of geostatistical analysis methods and mathematical physical methods to reveal the extent and scope of regional seawater intrusion,and finally to make a comprehensive evaluation of groundwater quality in the study area was carried out.The main conclusions of the thesis are as follows:（1）The main cationic order of groundwater in coastal areas of Shandong Peninsula is Na⁺>Ca²⁺>Mg²⁺>K⁺,and the anionic order is Cl^—>HCO₃^—>SO₄^2—.The chemical types of groundwater are Ca·Mg-SO₄·Cl,Ca·Mg-HCO₃,Na-SO₄·Cl and Na-HCO₃.The chemical types of fresh water are Ca·Mg-SO₄·Cl,Ca·Mg-HCO₃,Na-SO₄·Cl and Na-HCO₃,the chemical types of brackish water are Ca·Mg-SO₄·Cl and Na-SO₄·Cl,and the chemical types of brackish water are Na-SO₄·Cl.The main source of groundwater recharge in Shandong coastal zone is atmospheric precipitation,and evaporation and rock weathering also affect the evolution process.The results of principal component analysis show that the chemical characteristics of groundwater in Shandong Province are mainly affected by seawater intrusion and weathering of carbonate rocks.（2）The combined results of the fuzzy mathematical method and the single indicator method for determining the extent of seawater intrusion show that seawater intrusion exists to some extent in all cities in the Shandong study area,with the highest extent in the Weifang study area and the lowest extent in the eastern study areas of Qingdao and Weihai.The overall ranking of the extent of seawater intrusion in the study area is:Weifang>Yantai>Rizhao>Qingdao>Weihai.80%of groundwater samples in Weifang are affected by seawater intrusion,and 50%of groundwater samples in Longkou are affected by seawater intrusion.In 2018,2019and 2021,the maximum distance of seawater intrusion in Weifang is 18,20 and 19km,respectively.The evolution path of groundwater in three years is as follows:Ca-HCO₃→Na（Mg）-HCO₃-Cl→Na（Mg）-Cl-HCO₃→Na-Cl;In 2019,Na（Mg）-HCO₃-Cl→Na（Mg）-Cl-HCO₃→Na-Cl-SO₄→Na-Cl;2021 Ca-HCO₃→Na（Mg）-HCO₃-Cl→Na（Mg）-Cl-HCO₃→Na-Cl-SO₄→Na-Cl.（3）The results of salinity sources of groundwater in the Weifang study area from2018 to 2021 show that the main causal mechanisms of groundwater in the Weifang study area are evaporation and rock weathering,and the chemical characteristics of groundwater are mainly influenced by seawater intrusion,carbonate rock weathering and human activities.In Weifang area,62%of water samples were in desalination process and 38%in invasion process in 2018.20%of water samples were in desalination process and 80%in invasion process in 2019.2019 seawater invasion was more serious than 2018.50%of water samples were in desalination process and50%in invasion process in 2021.In contrast,56%of water samples are in the desalination process and 44%are in the invasion process in 2021 for the whole Shandong coastal area.This indicates that there is a trend towards further development of the extent to which groundwater in the Weifang study area is affected by seawater intrusion,but that other areas in Shandong are moving towards desalination.（4）The average content of metal elements in class was ranked as Sr>U>Mn>Ba>Fe>Zn>Cu（2019）.The metals did not exceed the standard in the study area,but the high values of Sr,Mn and Ba ion content all exist in the northern brine area of Weifang,which is speculated to be related to the invasion of salt water in Weifang area（points B1-B10）.Through the analysis of water quality index factor,the overall water quality in Shandong is good,but affected by seawater intrusion.37.7%of groundwater in Weifang has reached the poor water level.