Tracing heavy metal migration in stone coal mining watersheds: Insights from coupled SWAT-MIKE21-ECO lab simulations

Heavy metal contamination in riverine systems, particularly in regions affected by historical mining activities, poses significant environmental and health risks worldwide. This study investigates the migration and transformation of heavy metals (Zn, Cd, Ni, and Al) in the Xiaomixigou watershed, an abandoned anthracite coal mine area in Ankang, China, using a novel coupled two-dimensional numerical model integrating SWAT, MIKE21, and MIKE ECO Lab. The scientific novelty of this research lies in the integration of these models to simulate complex heavy metal dynamics in a mining-impacted watershed, providing a comprehensive understanding of pollution sources, transport mechanisms, and spatial distribution. Field sampling and laboratory experiments validated the model, revealing that Al is the most significant pollutant (8.00-9.15 mg L^-1), with concentrations decreasing downstream due to sedimentation and dilution. Zn and Ni showed similar trends, while Cd concentrations increased downstream, suggesting potential new pollution sources. The model's ability to simulate unmonitored areas and identify pollution hotspots offers critical insights for targeted remediation strategies. This study advances the field by demonstrating the efficacy of coupled hydrological, hydrodynamic, and water quality models in understanding and managing heavy metal pollution in complex watersheds globally.