Field evidence of environmental recovery after designed Technosol application in sulfide mine environment

Land degradation is a major environmental challenge in post-mining landscapes, where soil structure, fertility, carbon storage and potentially hazardous elements availability are severely compromised. Designed Technosols have emerged as a promising strategy for restoring soil functionality in such disturbed areas under different climatic conditions. Their effectiveness under field conditions over time requires systematic evaluation but these studies are scarce. A study was conducted at the São Domingos mine (Iberian Pyrite Belt, Portugal), where the first pilot project using designed Technosols for environmental rehabilitation was implemented in late 2020 (1.5 ha).

From the rehabilitation implementation system, physicochemical characteristics of Technosol and vegetation development have been monitored to understand the underlying temporal dynamics. Additionally, to physicochemical analysis in the soil samples collected periodically, the evolution of the temporal change was assessed via remote sensing for the area. Adjacent areas without Technosol application were used as control.

In general, mine areas without Technosol maintain their high environmental risk due to acid characteristics and high availability of potentially hazardous elements-PHE. Technosol remains their eutrophic and alkaline properties, supporting dense vegetation cover and improvement chemical characteristics of the area (pH, fertility and diminution of PHE spreading). Nonetheless temporal patterns following Technosol application have been observed.

For instance, Organic C and total N exhibited similar trends, with the highest values at implementation (130.58 g/kg and 7.92 g/kg, respectively), followed by a moderate decline over time, although it was statistically significant only after six months. C stock dynamics further supported these trends. Below-ground C stock increased gradually from (96.65 to 106.81 t C/ha) over 27 months and remained within the same overall range as the implementation, indicating high stabilization potential. Overall, Above-ground C stock increased from 11.55 to 108.85 t C/ha, peaking at 302.31 t C/ha after six months. Temporal evaluation using NDVI showed an increase in area and intensity of the index from 0.03 to 0.9. Overall, the grouped trends demonstrate that Technosols simultaneously promote biological activity, the improvement of C and N balance and enhance both below- and above-ground C stocks.

To evaluate the drivers of the rehabilitation system evolution, remote sensing products to derive topographic and hydrologic covariates (slope, aspect, topographic position, and connectivity proxies) are included to evaluate their influence on C stock, PHE availability and runoff connectivity in adjacent areas to the Technosol area. This study provides important indicators framework linking contamination dynamics and ecosystem recovery as well as the effectiveness of the environmental system with designed Technosol at long term.

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).