Abstract:
Rapid groundwater depletion from the northwestern Indian aquifer system in the western Indo-Gangetic
basin has raised serious concerns over the sustainability of groundwater and the livelihoods that depend
on it. Sustainable management of this aquifer system requires that we understand the sources and rates
of groundwater recharge, however, both these parameters are poorly constrained in this region. Here we
analyse the isotopic (d18O, d2H and tritium) compositions of groundwater, precipitation, river and canal
water to identify the recharge sources, zones of recharge, and groundwater flow in the Ghaggar River
basin, which lies between the Himalayan-fed Yamuna and Sutlej River systems in northwestern India.
Our results reveal that local precipitation is the main source of groundwater recharge. However, depleted
d18O and d2H signatures at some sites indicate recharge from canal seepage and irrigation return flow.
The spatial variability of d18O, d2H, d-excess, and tritium reflects limited lateral connectivity due to the
heterogeneous and anisotropic nature of the aquifer system in the study area. The variation of tritium
concentration with depth suggests that groundwater above c. 80 mbgl is generally modern water. In contrast,
water from below c. 80 mbgl is a mixture of modern and old waters, and indicates longer residence
time in comparison to groundwater above c. 80 mbgl. Isotopic signatures of d18O, d2H and tritium suggest
significant vertical recharge down to a depth of 320 mbgl. The spatial and vertical variations of isotopic
signature of groundwater reveal two distinct flow patterns in the aquifer system: (i) local flow (above c.
80 mbgl) throughout the study area, and (ii) intermediate and regional flow (below c. 80 mbgl), where
water recharges aquifers through large-scale lateral flow as well as vertical infiltration. The understanding
of spatial and vertical recharge processes of groundwater in the study area provides important baseline
knowledge for developing a sustainable groundwater management plan for the northwestern Indian
aquifer system.
