The southwestern coastal region of Bangladesh, encompassing 24 upazilas and Khulna City Corporation in the Khulna, Satkhira, and Jashore districts of the Ganges-Brahmaputra-Meghna delta. Groundwater salinization threatens freshwater security in this deltaic coastal setting, yet its seasonal variability, controlling hydrogeochemical processes, and spatial drivers remain unclear. A total of 110 groundwater samples from wet and dry seasons were analyzed to identify dominant geochemical mechanisms. Stable isotope data provided only qualitative support due to limited spatiotemporal alignment with groundwater sampling. A supervised machine learning framework compared Logistic Regression, Random Forest, XGBoost, and LightGBM to map salinity intrusion hazards, employing topographic, hydrological, and land-use predictors. Groundwater chemistry shifts from Ca–Mg–HCO₃ facies (wet) to Na–Cl facies (dry), indicating widespread dry-season salinization. Across 55 paired wells, mean electrical conductivity increased from 3964.6 µS/cm (wet) to 8653.8 µS/cm (dry), representing a statistically significant increase in regional salinity. Hydrochemical indicators suggest that salinization is driven not only by seawater mixing but also by reverse cation exchange and tidally influenced saline inputs. Elevated salinization is observed in the low-elevation southern coastal areas, particularly in Koyra and Shyamnagar, while inland Jashore is less affected. Results suggest that seasonal monsoonal freshening does not fully offset dry-season salt accumulation in shallow to intermediate groundwater in the southern coastal zone, although constrained by insufficient well-construction data. • Integrated hydrochemistry and ML for groundwater salinity-risk assessment. • Used paired data from 55 wells (110 samples) to quantify seasonal salinity. • Identified reverse cation exchange and marine/tidal saline inputs as key drivers. • Mapped higher salinity-intrusion risk in coastal areas than inland areas.
Tasneem et al. (Fri,) studied this question.