S. Hening J. Ganor B. Mayer C.E. Weyhenmeyer T.D. Bullen A. Paytan A. Vengosh 2007 <p><span>The geochemistry and isotopic composition (H, O, S, O</span>_sulfate<span>, C, Sr) of groundwater from the Nubian Sandstone (Kurnub Group) aquifer in the Negev, Israel, were investigated in an attempt to reconstruct the origin of the water and solutes, evaluate modes of water–rock interactions, and determine mean residence times of the water. The results indicate multiple recharge events into the Nubian sandstone aquifer characterized by distinctive isotope signatures and deuterium excess values. In the northeastern Negev, groundwater was identified with deuterium excess values of ∼16‰, which suggests local recharge via unconfined areas of the aquifer in the Negev anticline systems. The&nbsp;</span><i>δ</i>¹⁸<span>O</span>_H2O<span>&nbsp;and&nbsp;</span><i>δ</i>²<span>H values (−6.5‰ and −35.4‰) of this groundwater are higher than those of groundwater in the Sinai Peninsula and southern Arava valley (−7.5‰ and −48.3‰) that likewise have lower deuterium excess values of ∼10‰. Based on the geochemical differences between groundwater in the unconfined and confined zones of the aquifer, a conceptual geochemical model for the evolution of the groundwater in the Nubian sandstone aquifer has been reconstructed. The isotopic composition of shallow groundwater from the unconfined zone indicates that during recharge oxidation of pyrite to SO</span>₄<span>&nbsp;(</span><i>δ</i>³⁴<span>S</span>_SO4<span>&nbsp;∼−13‰;&nbsp;</span><i>δ</i>¹⁸<span>O</span>_SO4<span>&nbsp;∼+7.7‰) and dissolution of CaCO</span>₃<span>&nbsp;(</span>⁸⁷<span>Sr/</span>⁸⁶<span>Sr ∼0.70787;&nbsp;</span><i>δ</i>¹³<span>C</span>_DIC<span>&nbsp;</span><span>=</span><span>&nbsp;</span><span>−3.7‰) occur. In the confined zone of the aquifer, bacterial SO</span>₄<span>&nbsp;reduction removes a significant part of dissolved&nbsp;</span><span class="math"><span id="MathJax-Element-1-Frame" class="MathJax_SVG" data-mathml="<math xmlns=&quot;http://www.w3.org/1998/Math/MathML&quot;><mrow is=&quot;true&quot;><msubsup is=&quot;true&quot;><mrow is=&quot;true&quot;><mtext is=&quot;true&quot;>SO</mtext></mrow><mrow is=&quot;true&quot;><mn is=&quot;true&quot;>4</mn></mrow><mrow is=&quot;true&quot;><mn is=&quot;true&quot;>2</mn><mo is=&quot;true&quot;>-</mo></mrow></msubsup></mrow></math>"><span class="MJX_Assistive_MathML">SO42-</span></span></span><span>, thereby modifying its isotopic composition (</span><i>δ</i>³⁴<span>S</span>_SO4<span>&nbsp;∼−2‰;&nbsp;</span><i>δ</i>¹⁸<span>O</span>_SO4<span>&nbsp;∼+8.5‰) and liberating dissolved inorganic C that contains little or no radiocarbon (</span>¹⁴<span>C-free) with low&nbsp;</span><i>δ</i>¹³<span>C</span>_DIC<span>&nbsp;values (&lt;−12‰). In addition to local recharge, the Sr and S isotopic data revealed contribution of external groundwater sources to the Nubian Sandstone aquifer, resulting in further modifications of the groundwater chemical and isotopic signatures. In the northeastern Negev, it is shown that SO</span>₄<span>-rich groundwater from the underlying Jurassic aquifer contributes significantly to the salt budget of the Nubian Sandstone aquifer. The unique chemical and isotopic composition of the Jurassic groundwater (</span><i>δ</i>³⁴<span>S</span>_SO4<span>&nbsp;</span><span>∼</span><span>&nbsp;</span><span>+14‰;&nbsp;</span><i>δ</i>¹⁸<span>O</span>_SO4<span>&nbsp;</span><span>∼</span><span>&nbsp;</span><span>14‰;&nbsp;</span>⁸⁷<span>Sr/</span>⁸⁶<span>Sr ∼0.70764) is interpreted as reflecting dissolution of Late Triassic marine gypsum deposits. In the southern Arava Valley the authors postulate that SO</span>₄<span>-rich groundwater with distinctively high Br/Cl (3</span><span>&nbsp;</span><span>×</span><span>&nbsp;</span><span>10</span>⁻³<span>) low&nbsp;</span>⁸⁷<span>Sr/</span>⁸⁶<span>Sr (0.70734), and high&nbsp;</span><i>δ</i>³⁴<span>S</span>_SO4<span>&nbsp;values (+15‰) is derived from mixing with underlying brines from the Paleozoic units. The radiocarbon measurements reveal low&nbsp;</span>¹⁴<span>C activities (0.2–5.8 pmc) in both the northeastern Negev and southern Arava Valley. Taking into account dissolution of carbonate rocks and bacterial SO</span>₄<span>&nbsp;reduction in the unconfined area, estimated mean residence times of groundwater in the confined zone in the northeastern Negev are on the order of 21–38 ka, which suggests recharge predominantly during the last glacial period. The&nbsp;</span>¹⁴<span>C signal in groundwater from the southern Arava Valley is equally low but due to evidence for mixing with external water sources the residence time estimates are questionable.</span></p> application/pdf 10.1016/j.apgeochem.2007.01.005 en Elsevier New isotopic evidence for the origin of groundwater from the Nubian Sandstone Aquifer in the Negev, Israel article