Quantifying the dual role of river network density in cadmium accumulation from mining area (source) to agricultural...

Cadmium (Cd) contamination in croplands, often exacerbated by mining-polluted irrigation water, is a global environmental challenge. However, the role of river networks in modulating Cd transport and accumulation remains poorly understood, hindering targeted remediation. This study aims to bridge this gap by developing a novel basin-specific control framework that integrates pollution classification with river network zoning. We systematically compared the driving mechanisms of Cd contamination across different basin types using machine learning and modeling approaches on an extensive soil dataset. We innovatively quantified the interaction between mining activities and river network density (RD) and the critical RD thresholds. Our key finding reveals the dual role of RD, where dispersion at moderate levels (0.28-0.83 km/km²) mitigates Cd contamination, whereas retention (at RD < 0.28 km/km²) and flood irrigation (at RD > 0.83 km/km²) exacerbate Cd accumulation. Guided by these critical thresholds, we delineated regulatory zones and proposed tailored strategies within the risk-control basins. For Tier I croplands, source interception measures are recommended to curb Cd dispersion. For Tier II croplands, maintaining river connectivity and timely removal of sediments are essential. This RD-based framework offers a theoretical and practical tool for precise agricultural soil protection in mining-affected basins.