The Jiaodong Peninsula, a representative coastal region in eastern China, relies heavily on groundwater to sustain its socioeconomic development. The Jiaodong Peninsula is subject to the complex interactions among geological conditions, seawater intrusion, and intensive human activities; however, traditional methods struggle to distinguish between these sources, highlighting the need for quantitative assessments of pollution source attribution in the region. To investigate this, we systematically collected and analyzed 54 groundwater samples from Qingdao City, a typical case study in the southern Jiaodong Peninsula. A multi-methodological approach-including descriptive statistics, Piper trilinear diagrams, Gibbs plots, ion ratios, and the absolute principal component score-multiple linear regression (APCS-MLR) receptor model-was employed to characterize the hydrogeochemical evolution and quantify source contributions. Results indicate that the groundwater is generally weakly alkaline, with a mean total dissolved solids (TDS) concentration of approximately 1170 mg/L. While freshwater predominates inland, significant salinization is evident in coastal zones. Driven by seawater intrusion, the hydrochemical facies transition from HCO3 --Ca2+ type to Cl--Na+ type along the inland-to-coastal gradient, exhibiting typical coastal groundwater evolutionary signatures. Furthermore, elevated NO3 - concentrations highlight a substantial anthropogenic footprint. Ion ratio analyses suggest that the groundwater chemistry is co-governed by rock weathering, seawater intrusion, cation exchange, and agricultural/domestic pollution. Quantitative source apportionment via the APCS-MLR model revealed that (1) Factor 1 (halite dissolution and seawater intrusion) explained 86.4% of the variance in Na+ concentrations, 81.2% of the variance in Cl- concentrations, and 72.5% of the variance in TDS; (2) Factor 2 (natural water-rock interaction and salinization processes) explained 88.9% of the variance in Ca2+ concentrations and 75.8% of the variance in total hardness; and (3) Factor 3 (anthropogenic pollution) explained 84.3% of the variance in NO3 - concentrations and 91.5% of the variance in NO2 - concentrations, while also explaining 42.6% of the variance in SO4 2- concentrations. This study underscores that while natural processes remain fundamental, the superposition of seawater intrusion and human activities significantly reshapes the hydrochemical environment. These findings, derived from this representative case study in Qingdao, provide a scientific basis for groundwater resource protection and the mitigation of seawater intrusion and nitrate pollution across similar coastal settings in the Jiaodong Peninsula.
Gong et al. (Thu,) studied this question.