Characterization of recharge mechanisms in a Precambrian basement aquifer in semi-arid south-west Niger
Characterization of recharge mechanisms in a Precambrian basement aquifer in semi-arid south-west Niger
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DOI：
10.1007/s10040-018-1799-x
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发表时间：
2018-06
影响因子：
2.8
通讯作者：
Maman Sani Abdou Babaye;P. Orban;Boureima Ousmane;G. Favreau;S. Brouyère;A. Dassargues
中科院分区：
文献类型：
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作者：
Maman Sani Abdou Babaye;P. Orban;Boureima Ousmane;G. Favreau;S. Brouyère;A. Dassargues
在尼日尔西南部半干旱的达尔戈尔盆地中部，大部分地下水资源蕴藏于前寒武纪基底的裂隙含水层中。地下水资源的特点很差，这项研究是第一次尝试更好地描述补给机制和水文地球化学行为的含水层。水文地球化学和测压方法相结合，以确定补给率的变化和地下水的来源浅风化含水层和深裂隙/裂隙含水层。在流域尺度上，流向尼日尔河的地下水通量主要受地形影响，地下水位没有明显的长期趋势（1980-2009年）。水文地球化学特征以钙碳酸氢盐-镁（70%）型为主。它显示了从一个具有CO2和低矿化水（花岗岩类、蚀变岩）的开放环境向一个具有更多矿化沃茨（片岩）的封闭环境的演化。稳定水同位素（δ 18 O，δ 2 H）分析表明，地下水补给主要有两种机制：（1）直接补给，几乎没有降雨后分馏特征;（2）间接补给，来自蒸发的地表沃茨和/或河床。地下水氚含量表明，补给大多是最近的，年龄小于50年（3 H> 3 TU），只有10%表明过去几十年补给很少或甚至没有补给。根据氚的个别值估计的地下水更新率的中值相当于1.3%年-1，接近于20世纪80年代初的地下水样本确定的值，因此表明没有可测量的长期变化。
In the central part of the semi-arid Dargol Basin of southwestern Niger, most of the groundwater resource is contained in the fractured aquifers of the Precambrian basement. The groundwater resource is poorly characterized and this study is the first attempt to better describe the recharge mechanisms and hydrogeochemical behaviour of the aquifers. Hydrogeochemical and piezometric methods were combined to determine changes in recharge rate and origin of groundwaters for the shallow weathered aquifer and the deep fissured/fractured aquifer. At the basin scale, the groundwater fluxes towards the Niger River are influenced mainly by topography, with no visual long-term trend in groundwater levels (1980–2009). The hydro-geochemical signature is dominated by the calcic-bicarbonate to magnesian (70%) type. It shows evolution from an open environment with CO2and low mineralized water (granitoids, alterites) towards a more confined environment with more mineralized waters (schists). Stable water isotopes (δ18O, δ2H) analysis suggests two main groundwater recharge mechanisms: (1) direct recharge with nearly no post-rainfall fractionation signature and (2) indirect recharge from evaporated surface waters and/or stream-channel beds. Groundwater tritium content indicates that recharge is mostly recent, with an age less than 50 years (3H > 3 TU), with only 10% indicating low or even no recharge for the past decades. A median value of the groundwater renewal rate estimated from individual values of tritium is equivalent to 1.3% year−1, close to the one determined for groundwater samples dating to the early 1980s, thus indicating no measurable long-term change.