Assessment of seawater intrusion in coastal aquifers by modified CCME-WQI Indicators: Decadal dynamics in North Jiaozhou Bay, China

Seawater intrusion (SWI) poses a growing threat to groundwater sustainability in the northern coastal region of Jiaozhou Bay (NCRJB), China. Quantifying SWI impacts is critical for developing targeted groundwater management strategies. This study proposes an enhanced version of the Canadian Council of Ministers of the Environment Water Quality Index (CCME-WQI), which integrates eight hydrogeochemical indicators to evaluate SWI dynamics in both porous and fractured aquifers in NCRJB. Statistical analysis of 131 groundwater samples collected during 2010–2011 and 2020 demonstrated pronounced salinization in porous aquifers, with 90.11% of samples classified as exhibiting severe SWI impacts. Fractured aquifers exhibited increasing intrusion severity, with the proportion of samples indicating significant intrusion rising to 35.29% by 2020. The modified CCME-WQI outperformed conventional single-indicator assessment methods based on chloride concentrations by detecting nuanced ion-exchange mechanisms and freshening processes in aquifer systems. SWI in NCRJB is driven by the interplay of natural climatic variability and anthropogenic activities. Our results demonstrate the framework’s enhanced sensitivity to heterogeneous aquifers and its potential as a transferable tool for SWI assessment in coastal regions worldwide. This research highlights the urgency of implementing adaptive coastal groundwater management strategies while providing a scientifically robust methodology for global SWI monitoring and mitigation.