Soil chemical and functional indicators reveal limitations of restoration measures in abandoned metal mine soils of SE Spain: implications for ongoing and future management
摘要
Abandoned metal mine tailings remain long-term sources of contamination, and restoration measures aim to reduce contaminant mobility while supporting the recovery of key soil functions. This study evaluated the chemical and functional status of mine wastes, capping materials, and surrounding soils associated with previously restored mine tailings in the La Unión-Sierra de Cartagena mining district (SE Spain). Soils exhibited highly contrasting chemical conditions, ranging from strongly acidic to slightly alkaline (pH 2.6–7.8), with electrical conductivity reaching 10.5 dS m−1 in mining-affected sites. Total concentrations of Mn, Zn, Pb, Cd and As were high, reaching up to 35,960, 11,760, 36,340, 26 and 274 mg kg−1, respectively. Maximum concentrations exceeded regional Generic Values of Reference by up to two orders of magnitude for Mn and As, and by more than three orders of magnitude for Pb. However, total concentrations were poor predictors of contaminant mobility. Water- and ammonium acetate-extractable fractions revealed substantial metal(loid) availability in some capped soils, indicating that previously implemented restoration measures did not fully prevent contaminant mobilization. Rare earth elements were not enriched by mining activity, although enhanced mobility was observed locally under extremely acidic and saline conditions. Some capped soils exhibited signs of functional recovery. Carbonate-rich capping combined with vegetation establishment promoted partial recovery of organic matter pools and microbial activity, whereas mine wastes and sites capped with coarse mine-derived materials remained severely impaired. Overall, the results highlight the importance of integrating chemical availability and functional indicators to assess restoration effectiveness and guide management strategies in semi-arid mining environments.