Chemical tracing of salinity sources in Lake Kinneret (Sea of Galilee), Israel

Abstract

Lake Kinneret is a freshwater lake in northern Israel that receives a major part of its salt input from unmonitored springs that discharge through the lake’s bottom. We attempt to characterize the nature of these springs by estimating their chemical composition. While the springs around Lake Kinneret are subject to wide spatial and temporal variations in their ionic concentrations, specific sodium (Na), potassium, magnesium (Mg), strontium, bromine, and lithium to chlorine (Cl) ion ratios are almost constant within individual springs and spring groups. The radium : Cl ratio and the d 18 O‐Cl relationship confirm the notion that the spring waters result from recent mixing between saline brines and freshwater. Available compositional data from past years along with new analyses of the lake and its known springs allow identification of the salinity source that causes the observed deficit in the lake’s salt budget (e.g., 91‐93% chloride). The relative contributions from these saline springs are different for different ions; this contribution is highest for bromide (95%), decreases to 84% for Na, and is less than 50% for Mg. Two independent approaches have been used for balancing the salts in the lake, and they are as follows: (1) an annual mass balance between salt removal and supply of the different ions, assuming a steady-state lake; and (2) simulation of the lake’s evolution from 1964 (the beginning of salt removal from the lake via the Salinity Diversion Channel) until the present. Both methods predict very similar ionic ratios for the (yet unknown) average saline spring(s), testifying to the reliability of both approaches. The ionic ratios so obtained closely resemble Fuliya ( 6 Tabgha)-type waters, excluding the Tiberias and eastern shore springs as significant salt sources. This inferred composition of the average unmonitored springs depends strongly on present-day diversion of saline springs (this diversion thus prevents their flow into the lake). The different ionic ratios that identify the various spring groups reflect the respective compositions of the brine pockets that feed them. Our simulation also shows that the layered structure of Lake Kinneret enhanced the evolution rate of the lake after the implementation of the salt diversion program in 1964. Lake Kinneret (LK; Lake Tiberias or the Sea of Galilee) is a lake of immense historical and religious significance. It is also the only freshwater lake in Israel and the main water reservoir for the National Water Carrier (NWC)—the water supply system that transfers freshwater to central and southern Israel. About 30% of the country’s water supply was pumped from LK in 1995. Furthermore, with the water shortage in the Middle East becoming more and more acute, LK is also a waterbody of great political significance. The lake is monomictic; it is stratified between mid-March and December. The mixing of a fully stratified to a fully mixed lake takes about 4‐5 months. Though it is a flowthrough lake, it is significantly saltier than the Jordan River, which is its major water source (Table 1). The composition