Geogenic groundwater arsenic (As) contamination is pervasive in many aquifers in south and southeast Asia. It is feared that recent increases in groundwater abstractions could induce the migration of high-As groundwaters into previously As-safe aquifers. Here we study an As-contaminated aquifer in Van Phuc, Vietnam, located ~10 km southeast of Hanoi on the banks of the Red River, which is affected by large-scale groundwater abstraction. We used numerical model simulations to integrate the groundwater flow and biogeochemical reaction processes at the aquifer scale, constrained by detailed hydraulic, environmental tracer, hydrochemical and mineralogical data. Our simulations provide a mechanistic reconstruction of the anthropogenically induced spatiotemporal variations in groundwater flow and biogeochemical dynamics and determine the evolution of the migration rate and mass balance of As over several decades. We found that the riverbed–aquifer interface constitutes a biogeochemical reaction hotspot that acts as the main source of elevated As concentrations. We show that a sustained As release relies on regular replenishment of river muds rich in labile organic matter and reactive iron oxides and that pumping-induced groundwater flow may facilitate As migration over distances of several kilometres into adjacent aquifers.

在南亚和东南亚的许多含水层中，普遍存在地源性地下水砷（As）污染。人们担心，最近地下水抽取量的增加可能导致高砷地下水迁移到以前的砷安全含水层中。在这里，我们在越南范弗克研究了一个被砷污染的蓄水层，位于河内东南部约10公里的红河两岸，受大规模地下水抽取的影响。我们使用了数值模型模拟，以详细的水力，环境示踪剂，水化学和矿物学数据为约束，在含水层规模上整合了地下水流和生物地球化学反应过程。我们的模拟提供了人为诱发的地下水流时空变化和生物地球化学动力学的机械重建，并确定了几十年来砷的迁移速率和质量平衡的演变。我们发现，河床-含水层界面构成了一个生物地球化学反应热点，它是砷浓度升高的主要来源。我们表明，持续的砷释放依赖于定期补充富含不稳定有机物和反应性铁氧化物的河泥，并且抽水诱导的地下水流可能促进砷在几公里的距离内迁移到相邻的含水层中。我们发现，河床-含水层界面构成了一个生物地球化学反应热点，它是砷浓度升高的主要来源。我们表明，持续的砷释放依赖于定期补充富含不稳定有机物和反应性铁氧化物的河泥，并且抽水诱导的地下水流可能促进砷在几公里的距离内迁移到相邻的含水层中。我们发现，河床-含水层界面构成了一个生物地球化学反应热点，它是砷浓度升高的主要来源。我们表明，持续的砷释放依赖于定期补充富含不稳定有机物和反应性铁氧化物的河泥，并且抽水诱导的地下水流可能促进砷在几公里的距离内迁移到相邻的含水层中。