An integral soil quality index based on nematodes for mining-impacted Andean soils

Mining activities, while economically important, have caused significant soil degradation, affecting soil quality, ecosystem functioning, and sustainability in Andean ecosystems. This study developed an integral soil quality index based on physicochemical, microbiological, and nematode indicators to assess soil degradation in the Ollachea mining area, Peru. We collected soil samples from four land-use systems (natural pasture, Zea mays cultivation, Ficus sp. cultivation, and Eucalyptus sp. forest) during two dry and two rainy seasons. The proposed index integrates complementary indicators related to soil chemical properties, nutrient availability, metal contamination, microbial activity, and nematode community structure to characterize soil quality and detect ecological stress associated with mining disturbance. The results showed that the index effectively discriminated soil quality by land use and season, with Eucalyptus sp. forest soils showing the highest soil quality status, whereas cultivated and mining-impacted soils exhibited lower quality associated with greater environmental stress. The main contributors to soil stress were related to microbial and metal-associated indicators, particularly total actinomycetes (6.53), Al (1.87), and Fe (1.65), highlighting their relevance in mining-impacted soils. Furthermore, nematode-based biological responses increased the index's sensitivity to seasonal ecological changes. Compared with other soil quality indices, the proposed integral index performed better, showing strong correlations with soil quality patterns in both dry and rainy seasons (r = 0.97 and r = 0.95, respectively). Overall, this study shows that a nematode-enhanced integral soil quality index provides a robust, transferable approach for monitoring mining-impacted soils and supporting ecological restoration strategies in Andean ecosystems.