Deep sources of salinisation of Lake Kinneret, Israel - An isotope and rare earth approach

Full text: Salinisation of fresh groundwater reservoirs is a widespread problem, especially in arid regions. As a first step for protection it is crucial to identify its sources and mechanisms. The Jordan Rift Valley between Israel and Jordan is the deepest land depression on earth with the Dead Sea with -410 m below sea level, functioning as a receiving reservoir for the surrounding highlands. Groundwater quality changes drastically within sharp boundaries indicating an admixture of saline groundwater components of different origins. Lake Kinneret (Sea of Galilee), situated in the northern part of the Jordan Rift Graben, serves as an important drinking water reservoir for Israel and by treaty also for Jordan. The water quality is affected by an influx of saline groundwater by salty springs located at the lake shore but also within the lake and by an up welling seepage via the lake floor. More or less two main groups of theories exist about the primary origin of the salinity. One is that the salinisation derives by dilution of an ancient, intensively evaporated brine developed in a lake formed in the Rift Valley following seawater intrusion during late Miocene. The other is that the salinisation derives from dissolved evaporative sediments in a depth of 2000 meters or more. The existence of these sediments is not proven but strong hints exists. Based on isotope, Rare Earth elements and chemical data at least three different water types can be distinguished which all can be explained by mixing of more or less one original brine with recent young groundwater. (author)