Groundwater ages and reaction rates during seawater circulation in the Dead Sea aquifer

The Dead Sea system provides a unique opportunity to study flow velocities and reaction rates during seawater circulation in the aquifer. We present here a novel application of calculating groundwater age and velocity along the flow path of the hypersaline water from the Dead Sea into the aquifer using the buildup rate of Ra-228 in this water. The calculated circulation velocities are 1-10 m/y, which is in agreement with estimates based on the Na/Cl ratios in this water (1.5-4 m/y). The latter is unique to the Dead Sea-aquifer system, where the Na/Cl ratio has been decreasing during the past 50 years due to the precipitation of halite in the lake. The velocity estimates facilitated the calculation of the rates of water rock interactions in the Dead Sea aquifer.

SO4 is removed relatively fast (k = 0.8 y(-1)) due to gypsum precipitation while barite or celestine precipitation removes Ra-226 and Ba in a time scale of years (k = 0.22 y(-1)). Similar rates were found for redox-driven reactions, such as U removal (k = 0.4 y(-1)) and Fe and Mn contribution due to the dissolution of oxides (k = 0.15 y(-1)). In the fresh-saline groundwater transition zone, gypsum which precipitated from hypersaline water in higher lake stands, is now being dissolved and enrich the water with SO4. (C) 2013 Elsevier Ltd. All rights reserved.