Evaluating Long-Term Effectiveness of Managed Aquifer Recharge for Groundwater Recovery and Nitrate Mitigation in an Overexploited Aquifer System

Abstract. Managed aquifer recharge (MAR) has been widely recognized as an effective strategy for groundwater restoration and has been implemented globally. In the North China Plain, over-extraction of groundwater has led to a continuous decline in water levels, forming one of the world's most significant groundwater depressions. Recent riverine MAR operations have shown significant local groundwater recovery; however, the long-term regional fate and spatial evolution of nitrate remain poorly quantified. In particular, it remains challenging to assess how geological heterogeneity interacts with biogeochemical processes to control remediation efficacy. Most existing studies rely on short-term field monitoring and emphasize localized responses. This study, focusing on the Xiong'an depression area, develops a coupled flow and multi-component reactive transport model to evaluate the long-term impacts of MAR on groundwater recovery and the spatiotemporal evolution of water quality. The results indicate that MAR leads to a basin-wide mean groundwater level rise of 1.11 m, with a maximum increase of 7.5 m near the river. Nitrate reduction is dominated by physical dilution (∼ 91 %) rather than denitrification (∼ 9 %).Furthermore, geological heterogeneity governs the spatial variability of water quality evolution by channelling flow through preferential pathways, which creates localized reduction hotspots, despite having a minimal impact on the total nitrate mass removal. These findings highlight the dual hydrological and geochemical benefits of sustained MAR and provide quantitative insights for optimizing large-scale recharge strategies in overexploited aquifer systems.