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 (H-3) and stable isotopes (H-2 and O-18) to evaluate the source of recharge and aquifer dynamics. The shallow groundwater shows wide variation in isotopic signature (delta O-18: -11.3 to -5.0%o) reflecting multiple sources of recharge. The average isotopic signature of shallow groundwaters (delta O-18: -6.73 +/- 1.03 parts per thousand) is similar to that of local precipitation (-6.98 +/- 1.66%o) 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 (delta O-18: -8.6 parts per thousand) 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 (H-3: 5 - 10 T.U.) and deeper zone (H-3: 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.