Ten Years of Aided Phytostabilization in a Former Cu Mine: Evaluating Soil Recovery Under Different Amendment and Vegetation Strategies

Aided phytostabilization—combining soil amendments with tolerant vegetation—has proven effective in improving soil properties and reducing potentially toxic elements (PTE) mobility in polluted soils, yet long-term studies are scarce. This study evaluates the 10-year evolution of an ongoing (aided) phytostabilization field trial at a former Cu mine in NW Spain, comparing different strategies for soil recovery and PTE immobilization. The mine soil (Spolic Technosol) was extremely acidic (pH 2.7–3.6), toxic (51–108 mg kg−1 available [Cu]), organic matter- and nutrient-depleted, and virtually devoid of vegetation. Three amendments—compost (PC) and two technosols (PT1, PT2)—were assayed. Three planting treatments—Agrostis capillaris (AGR), Salix viminalis (SAL), and unplanted (UNP)—were established. Soil samples were collected before amendment applications and 1, 2, 3, 6, and 10 years after, and then analyzed for physicochemical properties. All amendments immediately improved soil properties, such as pH (5.3–7.0), CECe (41–59 cmolc kg−1), and nutrient concentrations (POlsen, exchangeable Ca, Mg, and K, or total C and N), and mitigated Cu availability (up to three orders of magnitude), thereby enabling vegetation establishment. Different amendments led to distinct initial trajectories that gradually converged toward a common pattern of long-term soil recovery. Aided phytostabilization effectively improved key soil chemical functions for over a decade; however, amendment choice should be aligned with site-specific recovery objectives and monitoring plans.