Sources of salinity in ground water from Jericho area, Jordan Valley.

Abstract

One of the major problems in the lower Jordan Valley is the increasing salinization (i.e., chloride content) of local ground water. The high levels of salinity limit the utilization of ground water for both domestic and agriculture applications. This joint collaborative study evaluates the sources and mechanisms for salinization in the Jericho area. We employ diagnostic geochemical fingerprinting methods to trace the potential sources of the salinity in (1) the deep confined subaquifer system (K2) of Lower Cenomanian age; (2) the upper subaquifer system (K1) of Upper Cenomanian and Turonian ages; and (3) the shallow aquifer system (Q) of Plio-Pleistocene ages. The chemical composition of the saline ground water from the two Cenomanian subaquifers (K1 and K2) point to a single saline source with Na/Cl approximately 0.5 and Br/Cl approximately 7 x 10(-3). This composition is similar to that of thermal hypersaline spring that are found along the western shore of the Dead Sea (e.g., En Gedi thermal spring). We suggest that the increasing salinity in both K1 and K2 subaquifers is derived from mixing with deep-seated brines that flow through the Rift fault system. The salinization rate depends on the discharge volume of the fresh meteoric water in the Cenomanian Aquifer. In contrast, the chemical composition of ground water from the Plio-Pleistocene Aquifer shows a wide range of Cl- (100-2000 mg/L), Na/Cl (0.4-1.0), Br/Cl (2-6 x 10(-3)), and SO4/Cl (0.01-0.4) ratios. These variations, together with the high SO4(2-), K+, and NO3- concentrations, suggest that the salinity in the shallow aquifer is derived from the combination of (1) upconing of deep brines as reflected by low Na/Cl and high Br/Cl ratios; (2) leaching of salts from the Lisan Formation within the Plio-Pleistocene Aquifer, as suggested by the high SO4(2-) concentrations; and (3) anthropogenic contamination of agriculture return flow and sewage effluents with distinctive high K+ (80 mg/L) and NO3- (80 mg/l) contents and low Br/Cl ratios (2 x 10(-3)). Our data demonstrates that the chemical composition of salinized ground water can be used to delineate the sources of salinity and hence to establish the conceptual model for explaining salinization processes.