The Verlorenvlei catchment on the west coast of South Africa is a semi−arid region that is growing progressively more reliant on groundwater due to increased variability in precipitation and increasing agricultural productivity. The groundwater systems have been put under additional stress given the recent 2015–2017 El Ninõ system that led to drought conditions along the west coast of South Africa. This increased reliance puts the natural environment and human dependence on groundwater into direct conflict. Groundwater was sampled for δ¹⁸O, δ ²H, δ ¹³C, ¹⁴C, ³H and ³H/³He ratios in addition to cation and anion concentrations from seventeen production boreholes and two springs in the catchment. Residence times were estimated using tritium and radiocarbon, and in the case of the latter, the Pearson Model has been used to correct for possible carbonate dissolution. Hydrochemistry and residence times of groundwater in the Verlorenvlei catchment have successfully been used to distinguish between the primary−porosity alluvial aquifer, the secondary−porosity Malmesbury shale aquifer (MG) and the fractured rock aquifers associated with the Table Mountain Group (TMG). Groundwater mixing has been identified within the catchment and this plays an important role in the variation in groundwater chemistry and residence time between the aquifer systems. The discrepancy between the calculated radiocarbon and ³H/³He ages in the TMG and alluvial aquifers has been evaluated using a lumped parameter model that confirms that the TMG is strongly dominated by young groundwaters. Young ³H/³He residence times calculated for groundwater in the TMG (34–57 years) and alluvial aquifers (34–47 years) implies that these systems are most susceptible to reduced groundwater recharge. Given the interconnected nature of the aquifer systems, reduced recharge rates into the TMG aquifer will decrease groundwater flow to both the alluvial and MG aquifer and this will impact the long−term sustainability of the RAMSAR listed Verlorenvlei estuarine lake and wetlands at the catchment outlet. Future residence time studies should consider using a lumped parameter model (LPM) to calculate the age distribution of groundwater in these aquifers as this would provide additional insight into the sustainability of the groundwater systems.

位于南非西海岸的 Verlorenvlei 集水区是一个半干旱地区，由于降水变化的增加和农业生产力的提高，该地区越来越依赖地下水。鉴于最近的 2015-2017 年厄尔尼诺系统导致南非西海岸出现干旱，地下水系统面临额外压力。这种增加的依赖使自然环境和人类对地下水的依赖直接冲突。对地下水进行 δ ¹⁸ O、δ ² H、δ ¹³ C、¹⁴ C、³ H 和³ H/ ^3采样除了来自流域中 17 个生产钻孔和两个泉水的阳离子和阴离子浓度之外，他还计算了比率。使用氚和放射性碳估计停留时间，在后者的情况下，Pearson 模型已用于校正可能的碳酸盐溶解。Verlorenvlei 集水区地下水的水化学和停留时间已成功地用于区分初级孔隙度冲积含水层、次级孔隙度马姆斯伯里页岩含水层 (MG) 和与桌山组 (TMG) 相关的裂缝性岩石含水层。已确定集水区内的地下水混合，这在地下水化学和含水层系统之间的停留时间的变化中起着重要作用。计算出的放射性碳与^{使用集总参数模型评估了 TMG 和冲积含水层中的3} H/ ³ He 年龄，该模型证实 TMG 主要由年轻的地下水主导。年轻³ H/ ³他计算的 TMG 地下水（34-57 年）和冲积含水层（34-47 年）的停留时间意味着这些系统最容易受到地下水补给减少的影响。鉴于含水层系统的相互关联性，降低 TMG 含水层的补给率将减少流入冲积层和 MG 含水层的地下水流量，这将影响 RAMSAR 列出的 Verlorenvlei 河口湖和集水口湿地的长期可持续性。未来的停留时间研究应考虑使用集总参数模型 (LPM) 来计算这些含水层中地下水的年龄分布，因为这将为地下水系统的可持续性提供额外的见解。