ABSTRACT The Lake Chad Basin (LCB) is an endorheic transboundary catchment highly vulnerable to drought. For effective groundwater management, recharge areas need identification and replenishment quantification. At present, little research exploring unsaturated zone water flow processes and groundwater recharge are available. In this study, 12 vertical soil profiles were analysed for stable water isotopes and chloride concentration to estimate evaporation and groundwater renewal. Most δ18O and δ2H isotope profiles reveal typical arid environment patterns, with maximum enrichment at depths between 2.5 and 20 cm and depletion towards the surface (atmospheric influence) and depth (mixing and diffusion). Average annual dry season evaporation rates in Salamat and Waza Logone range from 5 to 30 mm, in Bahr el Ghazal and Northern Lake Chad from 14 to 23 mm. According to the chloride mass balance (CMB), the average annual recharge rate is estimated between 3 and 163 mm in Salamat and Waza Logone and less than 1 mm in Bahr el Ghazal and Northern Lake Chad. Based on the CMB results, potential recharge sites were identified, while estimated soil evaporation corresponds to plant water use at the initial growing stage, which is an important component in irrigation water management.

中文翻译：

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使用稳定水同位素和土壤剖面氯化物的乍得湖盆地土壤水平衡

摘要乍得湖流域（LCB）是一个内陆跨界集水区，极易受干旱影响。为了有效管理地下水，补给区需要识别和补给量化。目前，关于非饱和带水流过程和地下水补给的研究很少。在这项研究中，分析了 12 个垂直土壤剖面的稳定水同位素和氯化物浓度，以估计蒸发和地下水更新。大多数 δ18O 和 δ2H 同位素分布显示典型的干旱环境模式，在 2.5 到 20 厘米深度之间最大富集，向地表（大气影响）和深度（混合和扩散）耗尽。Salamat 和 Waza Logone 的年平均旱季蒸发率从 5 到 30 毫米不等，在 Bahr el Ghazal 和北乍得湖从 14 到 23 毫米。根据氯化物质量平衡 (CMB)，Salamat 和 Waza Logone 的年平均补给率估计在 3 到 163 毫米之间，而在加扎勒河和乍得北部湖则不到 1 毫米。根据 CMB 结果，确定了潜在的补给点，而估计的土壤蒸发量对应于植物初始生长阶段的用水量，这是灌溉水管理的重要组成部分。