Abstract Northeastern Tunisia is a sub-humid region with annual rainfall ranging from 600 to 650 mm. Unconfined groundwater in this area is easily accessible and represents an important perennial water source for agricultural activities. The present study deals with a multi-parameter investigation of one of the most important basins in northeastern Tunisia: the Wadi Guenniche plain (130 km2). Hydrochemical (major elements and Br−) and isotopic (18O, 2H and 3H) investigations were carried out on 32 shallow wells to gain insights into groundwater recharge and salinity. The dominant water types were Ca–Mg/Cl–SO4 and Na/Cl with electric conductivity values varying between 0.86 and 6.6 mS/cm. Based on ion ratios and saturation indexes, groundwater salinity originated from weathering of carbonate and evaporite minerals and cation-exchange with clays. Additional influence of anthropogenic activities shown by high NO3− concentrations exceeding 100 mg/L was identified in different parts of the plain resulting from irrigation return flow. A six-year record of 18O and 2H signatures of daily rainwater (n = 293) enabled to define a Local Meteoric Water Line for the Bizerte area (δ2H = 7.02 δ18O + 8.27). The isotopic signature of groundwater was very similar to that of the mean annual rainfall in Bizerte suggesting direct recharge of the aquifer. Tritium levels in sampled wells were relatively high and indicated recent recharge and short residence time. Annual recharge of 100 mm was estimated using a mixing model based on 3H contents in precipitation and groundwater.

中文翻译：

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使用地球化学和同位素示踪剂来表征突尼斯北部 Wadi Guenniche 沿海平原的地下水动态和盐度来源

摘要 突尼斯东北部属半湿润地区，年降水量600～650毫米。该地区未封闭的地下水很容易获取，是农业活动重要的常年水源。本研究涉及对突尼斯东北部最重要盆地之一的多参数调查：Wadi Guenniche 平原（130 平方公里）。对 32 口浅井进行了水化学（主要元素和 Br−）和同位素（18O、2H 和 3H）调查，以深入了解地下水补给和盐度。主要的水类型是 Ca-Mg/Cl-SO4 和 Na/Cl，电导率值在 0.86 和 6.6 mS/cm 之间变化。根据离子比和饱和度指数，地下水盐分来源于碳酸盐和蒸发岩矿物的风化作用以及与粘土的阳离子交换作用。在灌溉回流导致的平原不同部分，确定了超过 100 mg/L 的高 NO3− 浓度所显示的人为活动的其他影响。每日雨水的 18O 和 2H 特征的六年记录（n = 293）能够为比塞大地区定义本地流星水线（δ2H = 7.02 δ18O + 8.27）。地下水的同位素特征与比塞大的年平均降雨量非常相似，表明含水层直接补给。采样井中的氚水平相对较高，表明最近的补给和停留时间较短。使用基于降水和地下水中的 3H 含量的混合模型估计 100 毫米的年补给量。