Application of Water Isotopes to Identify the Sources of Groundwater Recharge in a Karstified Landscape of Western Himalaya

Abstract

The spatial and temporal distribution of δ18 O and δD measurements of precipitation and groundwater were used to identify the recharge areas of groundwater/springs in a mountainous catchment of the western Himalaya. The δ18O and δD of precipitation showed marked spatial and seasonal variability with δ18O and δD varied from 0.1‰ to –13.0‰ and 1‰ to –74‰ with an average of –6‰ and –38‰, respectively. δ18O and δD of precipitation is strongly influenced by the basin relief and meteorology. The mean altitude gradient of –0.15‰ and –1.16‰ per 100 m change in elevation for δ18O and δD, respectively, was observed based on amount weighted mean precipitation isotopic values. The δ18O and δD in groundwater showed a narrow spatial and temporal variation in comparison to precipitation and varied from –6.8 ‰ to –10 ‰ and –58‰ to –38‰, with an average of –8‰ and –46‰, respectively. The most depleted (in heavier isotopes) isotopic values were observed in karst springs and most enriched (in heavier isotopes) isotopic values were observed in shallow groundwater samples. The results suggest that the groundwater with most depleted isotopic values have recharge areas at higher altitudes, whereas the groundwater with less depleted isotopic values have recharge areas at lower elevations. The climate change has shown the reduced snowfall and annual discharge in perennial karst springs i.e. 40-70%, besides seasonal springs dried up in recent years.