Characterization of Groundwater Chemistry Under the Influence of Seawater Intrusion in Northern Laizhou, Shandong Province, China

The rise in sea levels due to global warming and the excessive extraction of groundwater in coastal regions significantly encourages seawater intrusion, resulting in a cascade of ecological and environmental issues, including water quality degradation and soil salinization. The northern sector of Laizhou City, situated on the eastern coast of Laizhou Bay, exemplifies a typical location of seawater intrusion in China, where the rising salinity of groundwater has adversely affected local economic development and public health. This investigation involved the collection of 115 groundwater samples and 13 isotope samples from the northern region of Laizhou City. Statistical analysis, Piper’s trilinear diagrams, and various analytical techniques were employed to examine the chemical properties of the groundwater in the study area; characteristic ion ratios, Gibbs diagram, and hydrogen–oxygen isotope methods were utilized to analyze the sources of salinity and groundwater recharge; and a seawater intrusion groundwater quality index, which was applied to the present condition of seawater intrusion, was assessed utilizing the seawater intrusion groundwater quality index (GQISWI). The findings indicate that the chemical composition of groundwater in the research area is notably intricate. From freshwater to saline water, the groundwater chemistry transitions from Ca-HCO3·Cl-type water to Ca·Na-SO4·Cl-type water, and finally to Na-Cl-type water. Seawater intrusion in the research area is the primary cause of elevated groundwater salinity, alongside cation exchange and water–rock interactions that affect water chemistry. Seawater intrusion is predominantly focused in the northern region of the research area. The primary source of groundwater recharge is atmospheric precipitation.