Attending the 12th International Conference on Mine Closure

Last September, the 12th International Conference on Mine Closure was celebrated in Leipzig (Germany). This conference, organized by the Technical University Bergakademie Freiberg, is one of the world`s reference events among the mine closure professionals. The main conference topics that were discussed and that have been found as the main issues were:  establishing integrated life of mine planning, design sustainable land uses from the social and environmental perspective, increasing the post-mining assets value, and establishing  stable and self-regenerating ecosystems, among others.

Due to the urgent necessity of improving reclamation of mining areas, abandoned and/ or in transition to close, researchers from IRNAS-CSIC, University of Seville, University of Reading and Haute École Condorcet have collaborated to present a paper and an oral communication in this conference.

Gil-Martínez M, Domínguez MT, Navarro-Fernández CM, Crompot H, Tibbett M , Marañón T (2018). Long-term effects of trace elements contamination on soil microbial biomass and enzyme activities, in C Drebenstedt, F von Bismarck, A Fourie & M Tibbett (eds), Proceedings of the 12th International Conference on Mine Closure, Technical University Bergakademie Freiberg, Germany, pp. 633-644.

Results from the applied strategy of phytostabilisation on mining areas contaminated by heavy metals were presented. In our study area known as Guadiamar Green Corridor, where phytostabilisation have happened over 19 years, forestation has been found to improve soil fertility and microbial biomass, which is an indicator of improved soil quality. Moreover, different tree species have been found to affect soil chemistry and biology in different ways. White poplar was found to increase soil pH and to recover nutrients levels. However, stone pine was found to acidify the soil, increasing heavy metal availability and reducing microbial communities. In conclusion, previous to forestation is recommended to select the most suitable species for the specific conditions of the mining area to reclaim.

In this conference, Marta Gil-Martínez, predoctoral researcher from IRNAS-CSIC, had the opportunity to visit the Wismut Uranium Tailings Remediation Project , which started back in 1991 and currently clean-up, re-contouring and implementation of covers tasks are still in place. Last cover consists in revegetation to establish some forest and pastures areas, in order to maximize biodiversity.


The role of soil in the facilitation effect by the retama shrub

foto_retamasShrubs are considered to be hotspots of soil fertility and biological activity in dry ecosystems. The use of shrubs, like “retama” (Retama sphaerocarpa (L.) Boiss.), as nurse plants to facilitate woody plant recruitment has been proved to be particularly useful for the revegetation of highly disturbed environments, such as contaminated lands.

Researchers from IRNAS-CSIC, led by MT Domínguez, have studied the usefulness of the nurse effect for the revegetation of contaminated Mediterranean soils with Holm oak (Quercus ilex subsp. ballota). In particular, they have assessed whether the nurse effect is related to increases in soil fertility and microbial extracellular enzyme activities underneath the shrub plant, using the retama-Holm oak association as a model system. The study was conducted along a gradient of soil contamination in the Guadiamar River Valley, where afforestation with retama shrubs was conducted following a contamination episode.  Along this gradient, soil fertility and microbial activity from different microsites (bare soil, retama cover, Holm oak cover and retama + Holm oak cover) was analysed.

Thirteen years after the start of the remediation activities in the area, soil organic matter and nutrient content were scarcely influenced by the development of the vegetation, being similar across microsite types. Likewise, soil enzyme activities were more influenced by the background soil conditions (pH, and organic matter content, modified by the addition of soil amendment during soil remediation) than by the development of the vegetation. In the soils under the cover of the retama-oak association, intense acidification (pH <4) was observed in the most contaminated sites, which resulted in a higher solubility of toxic trace elements and lower enzyme activities (five times lower dehydrogenase and b-glucosidase activities, in comparison to neutral soils).

The results confirms previous evidence that in these systems the facilitation effect of the retama shrubs is more related to the improvement of abiotic conditions (light and extreme temperatures) than to soil biotic factors. They also suggest that improving soil conditions before plantation through amendment application is critical to ensure the improvement of microbial activity at the long-term in such degraded sites.

The study has been published in Ecological Engineering (available online 18 October 2016).


Domínguez, M.T., Madejón E., López-Garrido, R., Marañón, T., Murillo, J.M. 2016. Shrubs for the remediation of contaminated Mediterranean areas: is the nurse effect mediated by increases in soil enzyme activities? Ecological Engineering, 97: 577-581.