English abstract
Abstract An in-depth study of groundwater resources in Oman is urgently needed due to the rapidly increasing demand and limited sources. The resulted deficit in water resources calls for integrated water management based on scientific and precise studies for these resources. Combining both hydrochemistry and isotopic studies is an effective approach for reliable understanding of groundwater occurrence, degree of renewability and quality. The main objective of this study is to use the proposed methodology to trace the water provenance and identify the processes that affect groundwater quality. The study also aims to explore the age of water hosted by different aquifers as well as the hydraulic connectivity (mixing) between these aquifers. In total 198 samples representing precipitation, groundwater and Aflaj water have been collected through extensive field trips and associated hydrogeological investigations. The samples were analyzed for major ions and isotopes of '80, 2H, PH, WC, Sr/Sr. Chemical analyses and isotopic results were combined to characterize of the groundwater which is mainly hosted in HSG, Ophiolite, Alluvium and Tertiary aquifers in the study area. The rainfall analyses show that more than one rainfall mechanisms may be active at the same time. The southerly, northwesterly, and local convective patterns have been observed to be active in the same time during this study. The isotopic composition of groundwater and Aflaj water suggests southerly moisture source usually originates in the Arabian Sea. However, the isotopic compositions of groundwater and Aflaj water show that the high altitude moisture is the main source for HSG aquifer in addition to Daoodi and Ainy Aflaj whereas the moisture controlled by low altitude and evaporation mostly affect Ophiolite, Alluvium aquifers and Ghaily Aflaj. Processes related to water-rock interaction such as dissolution are found to be the main factors that control the chemistry of groundwater. The cation exchange and the evaporation also have a role in modifying the groundwater chemistry. Water of Aflaj from the surrounded rocks indicates a degree of dissolution rock-forming minerals mainly carbonates and silicates. The evaporation process is more effective in the Ophiolite, Alluvium and Tertiary aquifers in addition to Ghaily Aflaj. Although the contribution of the recent recharge is demonstrated, "C and geochemistry results showed that Ophiolite and Tertiary aquifers in the southern part of the study area hosting paleo groundwater suggest different recharge within approximate age of 10000 - 20000 B. P. Apparent connectivity between different rock units is confirmed by aquifers of HSG, Ophiolite and Alluvium in addition to Aflaj water with chemical and isotopic signature of different aquifers. Based on this investigation, it was found that the water rock interaction and evaporation processes are the main factors affecting the groundwater quality hosted by different aquifers in Northern Oman
