Geochemical Aspects of Groundwater in the Dead Sea Coastal Aquifer

The geochemistry of groundwater surrounding the Dead Sea reflects mixing between different water bodies that occupied the Dead Sea basin and fresh groundwater flowing from the highlands to the basin. The distribution of various geochemical parameters is affected by changes in the lake level, including natural fluctuations and the present lake level drop. This chapter deals with different aspects of groundwater flow mechanisms in the coastal aquifer of the Dead Sea and their relationship with the groundwater geochemistry. Dead Sea water circulation in the coastal aquifer occurs during a steady-state lake level but also persists during lake level drop. This interaction between the Dead Sea water and the sediments removes Ba, U, and 226Ra and contributes Fe, Mn, and short-lived Ra isotopes to the Dead Sea. 14C and tritium values in the Dead Sea groundwaters are affected by mixing with fresh water and between brines that occupied the Dead Sea Rift during different times. In addition to the inorganic water–rock interaction between the Dead Sea groundwater and the sediments, DIC δ13C, and S and O isotopes in dissolved SO4 suggest that methane oxidation coupled with bacterial sulfate reduction is taking place. On longer time-scales (glacial-interglacial), lake water penetrates the aquifer sediments during high stands and discharge back to the Dead Sea during low stands. The Ein-Qedem thermal springs composition suggests that the brine penetrated to the aquifer during the last glacial when the lake level was high and is discharging now back into the Dead Sea from a depth of about 1000 m.