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

Coal mining leaves behind extensive tailing dumps that pose long-term ecological and soil degradation challenges. This study evaluates the restoration potential of vegetation on coal mine tailings in the Jiu Valley, Romania, focusing on soil nutrient dynamics and the 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 their pH, organic carbon, macronutrients, micronutrients, and heavy metals using standardized spectrometric and titrimetric methods. Between 2021 and 2024, AV plots showed a 9.5% increase in total nitrogen and a 5.2% rise in organic carbon, alongside a 6.9% reduction in soil pH. HV plots exhibited a 10.6% increase in magnesium availability and a 2.8% decrease in copper concentrations, indicating active nutrient cycling. In contrast, UV soils retained 68% higher total potassium and 24% more zinc than vegetated plots, likely due to limited biological uptake. Lead concentrations remained below the EU threshold of 60 mg kg−1, while nickel levels exceeded recommended limits across all variants, peaking at 76.08 mg kg−1. The vegetation type significantly influenced nutrient mobilization and metal stabilization, with arboreal cover demonstrating the most consistent ameliorative effects. These findings underscore the role of targeted revegetation—particularly with Robinia pseudoacacia—in improving soil quality and mitigating ecological risks in post-mining landscapes.