Evaluation and Mechanism Study of Heavy Metal Pollution in Acidic Mine Drainage from the Xiaomi Creek Watershed

Acid mine drainage is an important source of heavy metal contamination in mining watersheds, posing persistent risks to aquatic environments and sediment quality. This study evaluated heavy metal pollution in water and sediments of the acid mine drainage-impacted Xiaomi Creek watershed, China. A total of 20 water samples and 13 sediment samples were collected and analyzed for manganese (Mn), lead (Pb), copper (Cu), cadmium (Cd), aluminum (Al), nickel (Ni), iron (Fe), and zinc (Zn). Water pollution was assessed using the single-factor exceedance index and the Nemerow composite pollution index, whereas sediment contamination was evaluated using the geoaccumulation index and potential ecological risk index. The results showed that water in the Xiaomi Creek watershed spanned a broad pH range (3.16–8.05), and heavy metal pollution was generally more severe in the main channel than in the tributaries, indicating a clear influence of upstream pollution inputs. Nickel showed the strongest enrichment in sediments and posed the highest ecological risk among the investigated metals, while Mn, Pb, Zn, and Ni exhibited severe sediment contamination. Overall, upstream stone coal mining activities and associated waste piles were likely major contributors to heavy metal pollution in the watershed, highlighting the need for source control, sediment-associated risk management, and risk-prioritized monitoring to support sustainable watershed management.