Isotope investigation on groundwater recharge and dynamics in shallow and deep alluvial aquifers of southwest Punjab

Groundwater samples collected from the alluvial aquifers of southwest Punjab, both shallow and deep zones were measured for environmental tritium (³H) and stable isotopes (²H and ¹⁸O) to evaluate the source of recharge and aquifer dynamics. The shallow groundwater shows wide variation in isotopic signature (δ¹⁸O: −11.3 to −5.0‰) reflecting multiple sources of recharge. The average isotopic signature of shallow groundwaters (δ¹⁸O: −6.73 ± 1.03‰) is similar to that of local precipitation (−6.98 ± 1.66‰) indicating local precipitation contributes to a large extent compared to other sources. Other sources have isotopically distinct signatures due to either high altitude recharge (canal sources) or evaporative enrichment (irrigation return flow). Deep groundwater shows relatively depleted isotopic signature (δ¹⁸O: −8.6‰) and doesn't show any evaporation effect as compared to shallow zone indicating recharge from precipitation occurring at relatively higher altitudes. Environmental tritium indicates that both shallow (³H: 5 – 10 T.U.) and deeper zone (³H: 1.5 – 2.5 T.U.) groundwaters are modern. In general the inter-aquifer connections seem to be unlikely except a few places. Environmental isotope data suggests that shallow groundwater is dynamic, local and prone to changes in land use patterns while deep zone water is derived from distant sources, less dynamic and not impacted by surface manifestations. A conceptual groundwater flow diagram is presented. - Highlights: • The environmental isotopic study of southwest Punjab groundwaters is presented. • Sources contributing to shallow and deep zone groundwater recharge are delineated. • Impact of irrigation return flow and canal water is limited to shallower depths at few places. • Hydraulic interconnection between shallow and deep zones is remote. • A conceptual groundwater flow model for southwest Punjab is presented.