Characterization of seawater intrusion based on multivariate statistical analysis and water chemistry characteristics:A case study of Laoshan district,Qingdao City

GANG Shenting; LYU Minghui; LU Qianqian; GAO Shuai; ZHAO Zhiqiang; CHEN Huanliang; PENG Tongqiang; WANG Xi; XING Liting; LI Lixia

doi:10.11932/karst20230509

Abstract：Groundwater is an important source of freshwater in coastal areas.With the rapid development of industrialization and urbanization,the water demand for production and living in coastal areas has been rising year by year.Therefore,the increasing exploitation of groundwater has triggered seawater intrusion and increasingly prominent environmental problems of groundwater in many places.Researching the hydro-chemical characteristics and evolutionary patterns of groundwater enables effective monitoring and protection of the groundwater environment. Taking the groundwater in Laoshan district,Qingdao City as the research object,we mainly focused on the issues of groundwater chemical characteristics,groundwater chemical processes,the degree of seawater intrusion and its impact on groundwater.In addition,under the theoretical guidance of hydrogeology,we analyzed the characteristics of seawater intrusion and evolution of groundwater hydrochemistry in the study area by means of data collection,theoretical analysis,field investigation and sample collection and testing.The research findings can provide a scientific basis for the rational development and utilization of groundwater in the area. The results show that the groundwater in the study area has Na+,Ca2+,Cl,and SO42-as the main dominant ions,and most of the groundwater chemistry types are Cl·SO4-Na and SO4·Cl-Ca·Mg types.The Cl-concentration in the groundwater varied considerably and its mean value exceeded the cut-off value for the presence or absence of seawater intrusion(250 mg·L-1),indicating that some degree of seawater intrusion may have occurred in groundwater.Groundwater in the Laoshan district of Qingdao City is neutral to weakly alkaline(mean pH=7.0-8.0),which is an effect of long-term hydrogeochemical processes in the coastal area.The results obtained by the PCA model show that changes in groundwater chemistry are mainly controlled by natural factors(rock-water interaction)or anthropogenic factors(agricultural and domestic activities).The five chemical characteristics of Cl-,mineralization,SO42-,γCl-/γHCO3- and SAR were selected as evaluation factors.Based on the inverse distance weighting(IDW)method and geographic information systems(GIS),we achieved the spatial mapping of seawater intrusion locations,showing that the seawater intrusion,in Laoshan district was mainly distributed in the intrusion sections such as the east of Jiangjia Tuzhai—the north of Puli community,the area of Wanggezhuang-Gangxi-Gangdong,Yangkou bay and the area of Danying village-Quanzhou island.The study results are of great significance for the use of groundwater resources and the prevention and control of seawater intrusion in Laoshan district.In addition,the research ideas and methods provide a reference for the study of groundwater genesis in other coastal areas in the world.