Groundwater recharge sources and processes in northwest India: Evidence from high frequency water isotope observations

Study region: Bist-Doab, Punjab, northwest India.Study focus: Water isotopes and specific electrical conductivity (SEC) are used in this paper to investigate groundwater recharge sources and processes in a catchment with a history of high groundwater abstraction for irrigation and canal irrigation. High frequency (every 10 days) samples for water stable isotope analysis (delta 18O and delta 2H) were sampled from a dense network of shallow (<50 m) and deep (>100 m) hand pumps and tube wells in Bist-Doab, northern Punjab between 2009 and 2014.New hydrological insights for this region: The study indicates that groundwater recharge is dominated by meteoric sources from high intensity events. However, in a small proportion of sites located in close proximity to some canals and rivers have significant surface water inputs. Isotope observations indicate rapid changes in groundwater recharge sources linked to post-monsoon pumping and seasonal connectivity to surface water inputs, even at some deep sites. Rapid changes are likely linked to poor well integrity, highlighting the risk to groundwater sources from surface water ingress. Shallow groundwaters had significantly higher SEC compared to deeper groundwater observations (p = 0.0002). Overall groundwater SEC is still relatively low (<2000 mu S/cm). However, based on previously published mean residence time of (<50 years) in shallow groundwater the high rate of change in salinity at some sites (2.5-10% per year) is of potential concern.