Implications of multi-decadal land use changes on groundwater regime in tropical coastal regions

Abstract

The present study investigates Odisha's coastal regions, analyzing Land Use and Land Cover (LULC) changes from 2009 to 2023 and their impact on land surface temperature (LST) and groundwater quality index (GWI) under increasing anthropogenic pressures. The findings revealed a 6.6% rise in built-up areas, a 25.6% increase in agricultural land, and a 4.2% decline in vegetation, with Kappa accuracies exceeding 80%. These changes corresponded to a 1.5 °C rise in mean LST. Hydrogeochemical analysis of 257 groundwater samples from Scenario 1 (2016–2017) and Scenario 2 (2022–2023) showed significant changes in water chemistry. Piper and Chadha diagrams indicated a transition from Na⁺-Cl⁻ to mixed Ca²⁺-Mg²⁺-Cl⁻ and Ca²⁺-Mg²⁺-HCO₃⁻ facies, reflecting a shift from saline to mixed water types and freshwater recharge. Despite this trend, scatter plots and molar ratios identified multiple contamination sources, particularly from anthropogenic activities. The GWI revealed that approximately 50% of the region falls into “poor” to “unsuitable” categories for drinking water, attributed to high levels of K⁺, Na⁺, and Cl⁻ in Scenario 1 and K⁺, HCO₃⁻, Na⁺, pH, and TH in Scenario 2, supported by ANOVA analysis. The increasing strong correlation between K⁺ and GWI further confirms the rise in agricultural activity. Gibbs diagram highlights rock-water interaction as the primary factor, with evaporation as secondary. The Ca²⁺ vs. SO₄²⁻ scatter plot highlighted carbonate weathering, contributing to increased groundwater hardness. TDS vs. TH correlation (>0.77) indicated worsening groundwater quality, with more samples transitioning to "very hard" and "brackish" categories. In contrast, strong correlations between TDS and Na⁺, Cl⁻ (>0.8) further confirmed increased salinity. Principal Component Analysis (PCA) revealed positive GWI and negative LULC loadings, linking urbanization and agricultural expansion to groundwater quality degradation. This study proposes sustainable water management (SDGs) strategies to fulfill SDGs 3, 6, and 11 enhancing coastal water resilience and public health.