干旱区生态环境知识资源中心

Arid to semi-arid conditions that generally promote water scarcity are common in many regions in the Near East. Moreover, various places in that geographic domain are affected by groundwater salinization. This challenge is also shared by the Jericho area, located on the western side of the lower Jordan Valley, about ten kilometres NW of the Dead Sea. Due to a unique hydrogeological situation in this area, the discrimination of the hydrochemical signatures of the possible sources of salinization are fuzzy. Part of the potentially salt bearing aquifer material was deposited by the high saline Pleistocene precursor of the Dead Sea, the Lake Lisan, and thus resembles the signature of known residual brines of the former lake. Brine occurrences at other locations in the area usually are connected to the western boundary fault, which is a structural element of the Dead Sea Transform system. From the study of the helium and neon noble gas isotope composition of samples from saline wells and springs at the northwestern Dead Sea shore as well as from six Jericho agricultural wells there is evidence that admixing brines are supposedly not the only source of salinization in the study area. Indeed it is shown that the highest helium excess concentrations are related to the vicinity of the border fault, where moderate salinities are already present. Wells not too far in the E of the study area but in close vicinity to Wadi Qilt produce groundwater with a noble gas composition typical for air-equilibrated surface water. This reflects significant volumes of infiltration in the rainy season due to the mountain discharge, that is mainly derived from springs in the upstream area of Wadi Qilt as well as run off. An intermediate position between the first two groups is demonstrated by the most saline groundwaters, which are found remote from the border fault in the E of the study area. This is interpreted as evidence for additional non-brine salinization input probably from the surrounding sediments of the Lisan Formation.