Salinity sources in coastal aquifers: Critical importance of sabkha deposits west of el bardaweil lake, North Sinai, Egypt

Author(s): M.A.Gomaa, T.Meixner, J.McIntosh

Salinization of aquifer waters is a pervasive problemworldwide. Increased salinity in groundwater can come froma diverse number of sources, among them dissolution of evaporites, evapoconcentration and seawater intrusion. Additionally, as groundwater becomes more saline geochemical evolution including exchange, precipitation and dissolution reactions can be facilitated and potentially alter water quality. In the current investigationwe use a set of groundwater physical and chemical observations from a region close to El Bardaweil lagoon on the Mediterranean coast of Egypt. We investigate seawater intrusion and evaporite dissolution of sabkha deposits as the origin of the variability in total dissolved solids in the aquifer system. In addition, we investigate the impacts of increased salinity on mineral equilibriumreactions and geochemical evolution of the groundwater system. The dissolution of evaporites is identified as the source of salinization in this system with those evaporites likely originating from the sabkha deposits found in the area.We also hypothesize that dolomitization is occurring in this system through the addition of Mg from dissolution of Mg-rich evaporiteminerals bymeteoric waters, and a resulting shift in saturation indices for dolomite. Themechanismwe propose differs fromexisting mechanisms in that it can occur in oxidizing environments and occurs after sabkha deposits are no longer in direct contact with seawater. The study also implies that development efforts by Egypt in the area to utilize Nile river water for agricultural purposes should proceed carefully as irrigated fields should be placed carefully to avoid dissolution of underlying evaporite deposits.

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