An isotopic approach to address the groundwater evolution and process in the Indus basin, NW India

Abstract

Groundwater recharge processes and connectivity between aquifers strongly influence the sustainability of groundwater use. In many intensively exploited alluvial systems, especially in semi-arid regions with intensive agriculture and multi-aquifer settings, both processes remain poorly understood. To address this gap, this study examines the spatial and temporal variations in groundwater isotopic composition (δ18O and δD) across shallow, intermediate, and deep aquifers in Punjab, India, a part of the Indus Basin, with the aim of identifying recharge sources, assessing evaporative influences, and understanding connectivity between the aquifers. In this regard, groundwater samples were collected during pre-monsoon, monsoon, and post-monsoon seasons and analysed for stable isotopes of oxygen and hydrogen. The δD-δ18O slopes for shallow (5.94) and intermediate depth aquifers (6.18) are observed to be lower than the Global (8) and Local Meteoric Water Lines (7.99), reflecting significant evaporative enrichment. The deep aquifers show relatively higher slopes during the pre- and post-monsoon seasons (>6.7), suggesting comparatively pristine water with limited evaporative modification. High d-excess values (>10‰) were observed in 9-22% of the samples, suggesting a contribution from glacialfed river and canal water. This contribution appears to be more pronounced in areas with intensive canal irrigation. Intermediate aquifers exhibit buffered seasonal isotopic variability; however, the close similarity in isotopic signatures between intermediate and shallow aquifers in certain regions suggests possible vertical leakage and hydraulic interaction between the two aquifer systems. Seasonal analysis of Δδ18O and Δd-excess reveals that most of the groundwater responds to rainfall infiltration and evaporation-driven enrichment, with canal-fed recharge dominating in areas adjacent to canal networks. This study provides an integrated isotopic perspective on recharge dynamics and inter-aquifer interactions in Punjab and emphasising the need for depthspecific groundwater management and protective measures to limit vertical connectivity and contamination risks. The findings have direct implications for sustainable groundwater use and policy interventions in agriculturally intensive regions of the Indus Basin.