Restoration Potential of Vegetation: Soil Nutrient Responses and Heavy Metal Distribution in Coal Mine Tailings

Coal mining leaves behind extensive tailings dumps that pose long-term ecological and soil degradation challenges. This study investigates the restoration potential of vegetation on coal mine tailings in the Jiu Valley, Romania, focusing on soil nutrient dynamics and heavy metal distribution. Field sampling was conducted across three vegetation types—unvegetated (UV), herbaceous (HV), and arboreal (AV, Robinia pseudoacacia)—at two intervals: three- and six-years post-plantation. Soil samples were analyzed for pH, organic carbon, macronutrients, micronutrients, and heavy metals using standardized spectrometric and titrimetric methods. Results showed that vegetated plots, particularly AV, exhibited significant improvements in total nitrogen, organic carbon, and base cation availability, alongside reductions in pH and certain heavy metals. HV plots demonstrated enhanced manganese and copper mobilization, while UV soils retained higher levels of total potassium and zinc, likely due to limited biological uptake. Heavy metal concentrations remained below European safety thresholds for lead and chromium, though nickel levels exceeded recommended limits across all variants. Vegetation type influenced nutrient cycling and metal stabilization, with arboreal cover showing the most consistent ameliorative effects. These findings underscore the role of targeted revegetation in improving soil quality and mitigating ecological risks in post-mining landscapes.