Dhaoui Z, Chkir N, Zouari K, Ammar F Hadj, Agoune A
Lab. of Radio-Analysis and Environment, Geology Dep, National School of Engineers of Sfax, Route de Soukra, BP 1173, 3038 Sfax, Tunisia.
Laboratory of Radio-Analysis and Environment, Faculty of Letters and Humanities, Geography Department, Route de El Matar, BP 1168, 3029 Sfax, Tunisia.
J Environ Radioact. 2016 Jun;157:67-76. doi: 10.1016/j.jenvrad.2016.03.005. Epub 2016 Mar 22.
Environmental tracers ((2)H, (18)O, isotopes of Uranium) and geochemical processes occurring within groundwaters from the Continental Intercalaire (CI) in Southern Tunisia were used to understand the hydrodynamics and the recharge conditions of this aquifer. This study investigates the chemical and isotopic compositions of the CI groundwater. The water types are dominated by Na(+), SO4(2-), Cl(-) throughout most of the basin with a general increase in total dissolved solids from the Saharan Platform margins towards the Chotts region. Large scale groundwater flow paths are toward the Chotts region. The stable isotopes composition of the analyzed groundwater ranges from -8.8 to -6‰ vs V-SMOW for δ(18)O and from -67 to -40‰ vs V-SMOW for δ(2)H. The relatively enriched stable isotopes contents suggest the contribution of the Dahar sandstones outcrops in the current recharge of the CI aquifer in an arid context. However, the most depleted values in heavy isotopes indicate a paleorecharge of the aquifer under wetter conditions revealing a long residence time of groundwaters. The results from water samples using alpha spectrometry method indicate a range in (238)U concentrations and (234)U/(238)U activity ratios (AR) of 0.044-1.285 μg kg(-1) and 1.2 to 8.84 respectively. The geochemistry of uranium isotopes in groundwater is controlled by many factors, essentially, the influence of water rock interactions, the preferential dissolution of (234)U relative to (238)U due to alpha recoil and the mixing processes between different waters with distinct AR as well as (238)U concentrations.
环境示踪剂（氘（²H）、氧-18（¹⁸O）、铀同位素）以及突尼斯南部大陆间层（CI）地下水中发生的地球化学过程被用于了解该含水层的水动力特征和补给条件。本研究调查了CI地下水的化学和同位素组成。在整个盆地的大部分地区，水的类型以钠离子（Na⁺）、硫酸根离子（SO₄²⁻）、氯离子（Cl⁻）为主，总溶解固体含量从撒哈拉地台边缘向肖特地区总体呈增加趋势。大规模的地下水流向肖特地区。分析的地下水的稳定同位素组成范围为：δ¹⁸O相对于维也纳标准平均海水（V-SMOW）为-8.8‰至-6‰，δ²H相对于V-SMOW为-67‰至-40‰。相对富集的稳定同位素含量表明，在干旱环境下，达哈尔砂岩露头对CI含水层当前的补给有贡献。然而，重同位素中最贫化的值表明该含水层在更湿润条件下的古补给情况，揭示了地下水的长停留时间。使用α能谱法对水样的分析结果表明，²³⁸U浓度范围为0.044 - 1.285 μg kg⁻¹，²³⁴U/²³⁸U活度比（AR）范围为1.2至8.84。地下水中铀同位素的地球化学受多种因素控制，主要包括水岩相互作用的影响、由于α反冲导致²³⁴U相对于²³⁸U的优先溶解，以及具有不同AR和²³⁸U浓度的不同水体之间的混合过程。
