Variation in δ¹⁸O and δ²H values of rainfall, surface water, and groundwater in the Sukhna Lake basin in northwest India

Sukhna Lake in the Himalayan foothills is a vital wetland with important ecological functions in north India. In the present study, we have collected water samples from rainfall (n = 482), surface water (n = 146), and groundwater (n = 404) during 2011–2017 for isotopic analysis (δ¹⁸O and δ²H) to understand the recharge processes in the Sukhna Lake basin. The δ¹⁸O and δ²H values of rainfall show seasonality across the study area due to the different vapor sources. The moisture source for precipitation is the Arabian Sea during the monsoon season (July–September) and from a westerly source during winters (December–January). The δ¹⁸O and δ²H values of the surface water bodies show an evaporative signature across the study area. We also observed spatial and depth-related variations in the δ¹⁸O and δ²H values of groundwater. Here, we categorized groundwater samples into two depth zones based on the surface topography, isotopic values of groundwater, and aquifer characteristics. The groundwater zone-1a-b (depth: < 65 m below ground level (bgl)) shows active recharge processes because of rainfall recharge and seepage from surface water bodies. We observed the dominance of precipitation recharge in groundwater zone-2 (depth: > 150 m bgl) due to the regional groundwater flow pattern. We suggest two groundwater flow patterns present in the study area: local flow system is limited to zone-1a-b, whereas the regional flow pattern can be seen in zone-2. The present study provides new insight into the study area's recharge mechanism to understand the hydrological processes in any lake basin.