Premium
Quantifying saline groundwater flow into a freshwater lake using the Ra isotope quartet: A case study from the Sea of Galilee (Lake Kinneret), Israel
Author(s) -
Raanan Hadas,
Vengosh Avner,
Paytan Adina,
Nishri Ami,
Kabala Zbigniew
Publication year - 2009
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.4319/lo.2009.54.1.0119
Subject(s) - hydrology (agriculture) , groundwater , flux (metallurgy) , salinity , saline water , seawater , geology , isotope , residence time (fluid dynamics) , oceanography , environmental science , environmental chemistry , chemistry , geotechnical engineering , physics , organic chemistry , quantum mechanics
We investigated the Ra isotope quartet in order to quantify the discharge of saline groundwater into a freshwater lake. The activities of 226 Ra, 228 Ra, 223 Ra, and 224 Ra were measured in the Sea of Galilee, Israel, surrounding saline springs, and the Jordan River, coupled with U, Th, and 226 Ra measurements in sediment cores and laboratory Ra adsorption experiments under different salinity conditions. The 226 Ra activity (0.007–0.008 Bq L −1 ) and 226 Ra : Cl ratio in the lake were significantly lower than those of the inflowing saline springs, indicating that 75‐86% of the incoming 226 Ra is removed from the lake water. This "missing" Ra is likely adsorbed onto suspended particles. Given the observed differential depletion of Ra isotopes, we present a model consisting of adsorption‐desorption, recoil, and decay of the short‐lived 224 Ra and 223 Ra isotopes. We predict a removal time of ~2 weeks for Ra, inferring the apparent residence time of suspended matter in the lake. A mass‐balance calculation of the different 226 Ra inventories reveals a saline groundwater flux of 44–61 × 10 9 L yr –1 for "Fuliyatype" water. The residence time of dissolved 226 Ra in the lake is estimated as 3–4 yr. The 228 Ra : 226 Ra ratio of the lake water and a mass‐balance calculation show that 228 Ra arrives from regeneration though bottom sediments, in addition to groundwater flux. Mass‐balance calculations of the expected saline fluxes before the diversion of saline inflows to the lake (early 1960s) provide 226 Ra activity estimates in the lake (0.018‐0.020 Bq L −1 ) that are similar to the value (0.018 ± 0.0001 Bq L −1 ) measured in the lake in 1962.