Multi-scale assessment of land use and land cover dynamics on groundwater quality in the south-central coastal region of Bangladesh

This study investigated the impact of Land Use and Land Cover (LULC) changes on groundwater quality in two south-central coastal districts of Bangladesh over an 18-year period (2000–2018). Satellite-derived LULC classification revealed an 883% increase in urban area, while agricultural and barren lands declined by 4.92% and 33.25%, respectively. Groundwater quality was assessed using Na⁺, Cl⁻, and NO₃⁻ concentrations in shallow and deep aquifers. Spatial analyses indicated widespread exceedances of Bangladesh’s drinking water standards, particularly in the shallow aquifer. Elevated Na⁺ and Cl⁻ levels suggest salinity intrusion, while high NO₃⁻ concentrations, especially in agricultural zones, points to fertilizer leaching. In contrast, deep aquifer, likely protected by thick aquitard, exhibited lower ion concentrations. Correlation analyses between 2018 LULC types and groundwater quality revealed positive associations between agricultural and urban areas with NO₃⁻ in the shallow aquifer, while vegetation correlated negatively with all ions. Barren lands near saline waterbodies correlated positively with Na⁺ and Cl⁻. Deep aquifer showed weaker correlations, supporting its relative isolation from surface influences. One-way ANOVA confirmed statistically significant differences between the aquifers (all p<0.001), with higher concentrations in shallow groundwater. Boxplots showed elevated medians and wider interquartile ranges in shallow aquifer, indicating greater variability and susceptibility to contamination, whereas deep aquifer remained more stable. Water Quality Index (WQI) assessments also indicated consistently better water quality in the deep aquifer across most of the study area. This integrated approach helps identify poor water quality hotspot and inform sustainable land and water resource management strategies in vulnerable coastal regions.