A study published in Hydrogeology Journal https://doi.org/10.1007/s10040-026-03078-3 provides new insights into the sources of groundwater salinization and inter-aquifer mixing dynamics in Siwa Oasis, Egypt, an arid environment where groundwater is essential for agriculture and local water resources.
Groundwater resources in Siwa Oasis, Egypt, are increasingly threatened by salinization and intensive abstraction. A multi-method investigation combining hydrochemical analysis of 153 water samples, self-organizing maps, stable and radiogenic isotopes, radiocarbon dating, inverse geochemical modelling, and 3D numerical modelling was conducted to identify the sources of salinity and quantify groundwater exchange between the shallow Tertiary Carbonate Aquifer (TCA) and deep Nubian Sandstone Aquifer (NSSA). The results demonstrate that salinization is driven by multiple processes, including evaporation, hypersaline lake infiltration, and agricultural return flows. Fault systems act as important pathways for freshwater transfer from the deep NSSA, contributing 52–90% of the water volume in the shallow aquifer. However, continued groundwater abstraction is projected to cause 30–40 m of drawdown by 2100, reducing this freshwater contribution and potentially accelerating salinization. The study highlights the need for integrated management of connected aquifer systems, improved irrigation efficiency, protection of fault-controlled flow pathways, and long-term groundwater monitoring.
