Soil and vegetation diversity responses to designed Technosol applied in a sulfide mine under semi-arid conditions: field evidence at long term

The recovery of sulfide mine areas using designed Technosols and vegetation is often evaluated under controlled conditions, whereas field-scale evidence remains scarce. The first pilot (1.5 ha) with designed Technosols, produced from agro-industrial and urban wastes, was installed at the São Domingos mine (Iberian Pyrite Belt, Portugal)in two areas subject to continuous leaching of acid mine drainage, for environmental recovery purpose. An adjacent area without Technosol was used as control. The areas with and without Technosol were sown with a commercial herbaceous mixture including some autochthonous shrub species. After 4.5 years from recovery system (Technosol+vegetation) installation, the physicochemical quality of soil (pH, EC, fertility, nutrients and potentially hazardous elements-PHE availability) and the vegetation status (species composition, % cover, total biomass, seed bank diversity) were evaluated. A total of 25 randomly distributed sampling points were established with both soil and vegetation samples collected at each point (T1-Technosol area: 15, T2-Technosol area 2: 5, control: 5). The aim of the study was to evaluate the chemical quality of soil and vegetation status in the Technosol and control areas at long-term.

The application of the designed Technosol significantly improved the soil quality of the mine area compared to the control, increasing pH (from 4.08 to 7.76) and organic C content (62.49 vs. 2.42 g kg⁻¹). The available fractions of macronutrients were higher in the Technosols areas while available PHE amounts were approximately 73% lower than in the control area. Vegetation reflected soil improvement, with 20 taxa (10 families) registered and higher family richness in the Technosol areas (10 vs. 4) .Technosols areas were dominated by Poaceae and Asteraceae showing almost complete soil cover (~96%). The control area was barely covered (<9%) mainly by Poaceae with Linaceae and Brassicaceae. The soil seed bank showed higher plant diversity in Technosols samples (8 families), while no germination was recorded in the control (assay conducted under controlled conditions for 3 months).

Comparing the two areas with Technosol, no remarkable differences was obtained for pH (7.75–7.78 and low PHE availability but EC EC (500.6 vs. 236.4 µS/cm), available P content (321.7 vs. 191.1 mg kg⁻¹) and CEC (61.1 vs. 46.6) were different. Despite the application of similar Technosol and seeding, the plant communities diverged for the plant diversity (8 families vs. 5) and dominance of grasses. Although the vegetation cover and biomass amounts were similar between the Technosol areas, a differentiation of the carbon stock obtained (948.8 vs. 645.2 g C/m^-2). Seed bank family richness was similar (6 families each) but composition differed Poaceae, Asteraceae, Urticaceae and Apiaceae families were common, while presence of Brassicaceae and Solanaceae or Malvaceae and Amaranthaceae depended on the Technosol area. This field case study provides a practical workflow linking soil improvement, contamination dynamics and vegetation recovery. It highlights the effectiveness of Technosol in environmental recovery of sulfide mine areas at long term and the spatial heterogeneity evolution.

This work was funded by national funds through FCT—Fundação para a Ciência e a Tecnologia under the projects UID/04129/2025 (LEAF) and LA/P/0092/2020 (TERRA).