Stable isotope evidence on mechanisms and sources of groundwater recharge in quaternary aquifers of Kelantan, Malaysia

Abstract

The groundwater from shallow alluvial aquifers of northern Kelantan, Malaysia, was analysed for stable isotopes (δ18O and δ2H) during northeast and southwest season to assess the dynamics of the recharge processes. The groundwater shows quite a large variation in isotopic signatures (18O ranges from -7.5 to 0.62 ‰ for northeast (NE) and from −7.4 to −4.98 ‰ during southwest (SW)). These values reflect the contribution of different recharge sources in the aquifer. During NE season, the average isotopic signature of groundwater (δ18O: −5.30‰) is similar to the rainfall (δ18O: −4.13‰) indicating that rainfall is the main source of recharge compared to the other sources. The SW season shows an isotopically distinct signature due to contribution from surface water bodies (river sources) and enriched irrigation return-flow. Interestingly, the groundwater average isotope signature in SW season (δ18O: −6.40‰) is very close to the surface water (δ18O: −6.47‰), indicating significant contributions from surface water bodies of the area. Overall, the isotope data suggests that shallow groundwater is very dynamic during SW season whereas in NE the impact of surface manifestations is less. The study highlights the significance of further studies to accurately quantify the recharge volumes from different sources that will help to model and manage the aquifers both qualitatively and quantitatively. Moreover, the quantification of irrigation return-flow is very essential component keeping in view the contaminant transport from the agricultural areas.