ABSTRACT

We examine groundwater recharge processes and their relationship to rainfall intensity in the semi-arid, southwestern Lake Chad Basin of Nigeria using a newly compiled database of stable isotope data (δ²H, δ¹⁸O) from groundwater and rainfall. δ¹⁸O signatures in groundwater proximate to surface waters are enriched in ¹⁸O relative to regional rainfall and trace focused groundwater recharge from evaporated waters via ephemeral river discharge and Lake Chad; groundwater remote from river channels is comparatively depleted and associated with diffuse recharge, often via sand dunes. Stable isotope ratios of O and H (δ²H, δ¹⁸O) in groundwater samples regress to a value along the local meteoric waterline that is depleted relative to weighted mean composition of rainfall, consistent with rainfall exceeding the 60^th percentile of monthly precipitation intensity. The observed bias in groundwater recharge to heavy monthly rainfall suggests that the intensification of tropical rainfall under global warming favours groundwater recharge in this basin.

摘要

我们使用来自地下水和降雨量的稳定同位素数据（δ ² H、δ ¹⁸ O）的新编译数据库，研究了尼日利亚半干旱的乍得湖盆地西南部的地下水补给过程及其与降雨强度的关系。靠近地表水的地下水中的δ ¹⁸ O 特征相对于区域降雨量而言富含¹⁸ O，并通过短暂的河流排放和乍得湖追踪蒸发水体的集中地下水补给；远离河道的地下水相对枯竭，并且通常通过沙丘进行扩散补给。O 和 H 的稳定同位素比（δ ² H，δ ¹⁸O) 在地下水样本中，回归到沿当地大气水线的值，该值相对于降雨的加权平均成分枯竭，与超过月降水强度^第60^个百分位的降雨量一致。观察到的地下水补给偏向于每月强降雨表明全球变暖下热带降雨的加剧有利于该盆地的地下水补给。