Hydrochemical processes in the lower Jordan valley and in the Dead Sea area

Abstract Changes in the concentrations of major, some minor and trace elements occurring in both surface and groundwater of the lower Jordan River–Dead Sea drainage basin have been investigated in order to identify the characteristics of the regional aquifers and their recharge areas. Spider patterns of elements and rare earth distribution patterns pinpoint the characteristic chemical features of groundwater. As compared to seawater, the high Br/Cl ratios in groundwater are caused either by high Br/Cl ratios in precipitation, by leaching of Br from bituminous matter or by mixing with brines beyond the epsomite stage. The locations of groundwater samples with enhanced B contents coincide with the distribution of gypsum in the beds of the Lisan Formation, which produces water with nearly constant B/SO 4 2− molar ratios. Aeolian distribution of the unconsolidated Lisan sediments influences the B/SO 4 ratio in the area of Lake Tiberias and in the Jordan Highlands. The high Gd anomaly in the Dead Sea water is of geologic origin whereas that in the Jordan River and in Nahal (stream) Qidron is largely anthropogenic. The anthropogenic Gd input to the Dead Sea is insignificant compared to the actual amount in the water of the Dead Sea. Hot saline water encountered along the western shores of the Dead Sea with high Gd anomalies indicate that they contain large amounts of ancient Dead Sea water that mix (as hot ascending brines) with fresh water. The recharge area of groundwater in the lower Jordan Valley extends largely over limestone and dolomite outcrops of the Upper Cretaceous Judea Group. Weathering of locally underlying Lower Cretaceous volcanics in the area of Pezael–Beqaot, and Argaman yield groundwater with δ 34 S(SO 4 2− ) values ranging from − 2 to + 4‰. The presence of sulphide-bearing bodies in this area is attested to magnetic anomalies detected at depths of several kilometres. δ 34 S(SO 4 2− ) indicates very deep groundwater circulation. High δ 34 S(SO 4 2− ) > 15‰ is typical for marine sulphates from the Judea and Avedat Group limestone. The springs located along the northwestern shore of the Dead Sea discharge water replenished on the eastern Judea Mountains. The increase in the salinity of this water is due to brines flushed from sediments and from adjacent sedimentary rocks, which host entrapped brines from the precursors of the Dead Sea formed during the late stages of Lake Lisan. Fresher water flushes out these residual brines as a result of falling sea level. Salinity increase in groundwater is also affected by the ascent of deep-seated hot brines from pre-Sedom periods along the Rift faults. Calculations of mixing between fresh and highly saline end-members show that leaching of anhydrite from sediments, precipitation of calcite, formation of dolomite, albitization of plagioclase and ion exchange with abundant clay minerals control the major-element composition of the saline groundwater.