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.


Research Conference on soil remediation and ecosystem services

The mine accident occurred in Aznalcóllar (Sevilla) in April 1998 was a large-scale catastrophe of important ecological and socioeconomical consequences. The cleaning up and remediation of the soils contaminated with trace elements, the following afforestation, and the creation of a protected area – The Guadiamar Green Corridor – is a restoration case study of international relevance.

On the occasion of the 20th anniversary of the mine accident, this April 26th 2018 the IRNAS, CSIC has organized a Research Conference on Soil remediation and ecosystem services. The inauguration was presided by José Enrique Fernández (Director of IRNAS), Isabel González (Director of the Doctorate Program on Natural Resources and Environment, University of Seville) and Margarita Paneque (CSIC Delegate in Andalusia).

The Conference consisted of six panel presentations and one round table. In the first talk Miguel Ferrer (EBD, CSIC), who was Director of the Doñana Biological Station in 1998, presented a historical perspective of the ecological impacts of the mine-spill and the learnings to prevent this type of accidents.

Francisco Cabrera (IRNAS, CSIC) and Emilio Galán (University of Seville) addressed the problems derived from soil contamination by trace elements, and the measures to remediate them. Paula Madejón (IRNAS, CSIC) presented the soil remediation measures evaluated by the IRNAS for the European project RECARE, and exhibited a video recorded by Viverra Films.

María Teresa Domínguez (University of Seville) remarked the ecosystem services, in particular of regulation, provided by the remediated soils in the Guadiamar. Francisco Quirós (Andalusian Government) stated that the current management objective for the Protected Landscape Guadiamar Green Corridor is to consolidate the ecological corridor for biodiversity conservation, and the enhancement of ecosystem services, especially those of regulation and cultural.

Photo: Bruno Sester (CSIC)

The Conference finished with a round table moderated by Teodoro Marañón (IRNAS), about the topic “A recovered natural area: challenges and opportunities”. There was a consensus indicating that the main scientific and technical challenge, after the mine spill, was the quick cleaning up and remediation of the contaminated land. Among the opportunities, it was remarked the creation of a new protected area, and its function as ecological corridor, promoting biodiversity conservation. From the scientific perspective, there was the opportunity of having a natural laboratory where to test and evaluate remediation techniques for soils contaminated by trace elements. In this sense, it was very relevant the transfer of knowledge and technology acquired during these 20 years post-accident, and the potential application in similar cases.

Measures to remediate contaminated soils: the Guadiamar case study

Soil pollution is one of the main environmental problems at a global scale. Within the European RECARE project, several threats of soil degradation are investigated, and measures and solutions to remediate degraded soils are proposed.

A research team from the IRNAS, CSIC participating in the RECARE project has contributed with the evaluation of remediation measures for contaminated soils in the case study of the Guadiamar Green Corridor (Seville, Spain). The implementation of a phytoremediation process in three stages was proposed: amendments addition, planting of trees and monitoring of the system.

1) Firstly, results were presented showing a long-term study (from 2002 to 2016) where two types of amendments (sugarbeet lime and biosolid compost) were applied to a contaminated soil. The treatment effectiveness was evaluated by measuring the produced plant biomass and the trace element (TE) concentration in plants, as well as the transfer of TE from soil to plants. The lime-rich inorganic amendments were very effective increasing soil pH and therefore reducing TE availability (mobility); while the organic amendments were effective compensating the organic matter loss in the soil.

2) Secondly, the soil remediation effects of seven tree species (Populus alba, Celtis australis, Fraxinus angustifolia, Quercus ilex, Olea europaea, Ceratonia siliqua and Pinus pinea) planted in the contaminated area were investigated. Concentration of TE in leaves and roots of trees, and in the soil underneath was measured in 2014 (about 15-year-old trees). The capacity to phytostabilize soil TE by different tree species was evaluated based on the retention of TE in roots and the low translocation of TE from roots to leaves.

3) Thirdly, in this phytoremediation process of contaminated soils is crucial the long-term monitoring of soil availability of TE and their concentration in the living organisms (plants and animals) composing the trophic network. The continuous evaluation of those results will modify the following remediation measures within an adaptive management cycle.

This work has been published in the special issue of the journal CATENA, entitled “Testing Soil Conservation”, compiling the results of the different case studies within the European RECARE project.

Madejón P., Domínguez M.T., Gil-Martínez M., Navarro-Fernández C.M., Montiel-Rozas M.M., Madejón E., Murillo J.M., Cabrera F., Marañón T. (2018) Evaluation of amendment addition and tree planting as measures to remediate contaminated soils: The Guadiamar case study (SW Spain). Catena 166: 34-43.

Conference about ecosystem services in Córdoba University

The RESTECO researcher María T. Domínguez has given the conference “Soil contamination and provision of ecosystem services in the Guadiamar River Basin”, within the Open Classroom program of the University of Córdoba, Spain, on May 9th 2017.

In the conference, the main concepts relative to the role of soil provisioning ecosystem services were introduced. The Guadiamar River Valley was presented as a case study, where many works focused on the impact of soil contamination on the provision of ecosystem services have been carried out.

Biology degree students visit the Guadiamar River

On March 24th, the students of the subject “Ecology of Global Change: Current Transition of the Biosphere” visited the Guadiamar River basin. The subject belongs to the Biology degree of the University of Seville (US).

The objective of the excursion was to carry out an ecological and environmental analysis of the landscape and ecosystem transformations produced by the anthropic action during centuries in the outskirts of the city of Seville. The Guadiamar River, because of its ancestral importance as a source of water and resources, is a good example of these transformations that can be observed from its birth in the Sierra Norte until its mouth in the Guadalquivir River, in the marshes of the Doñana Park.

The professors María Cruz Díaz Antúnez-Barradas (US) and María José Leiva Morales (US) described the different ecosystems where the Guadiamar River flows. In its high part, in the mountain range, the Guadiamar River crosses forests and plantations of eucalyptus trees. In the middle section, the amplitude of the fluvial valley appears increasing riverside vegetation in the borders and meadows in the high zones. Further down, the river enters the Protected Landscape of the Guadiamar Green Corridor where the forest of the alluvial plains was reforested with Mediterranean shrubs and trees (oaks, olive trees, brooms, etc.), while the forest gallery shows poplars, ash trees and willows. Finally, in the low section, it ends in the marshes of Doñana, where crops of rice and brackish pastures appear.

At the Doblas stop (Sanlúcar la Mayor), Marta Gil Martínez (IRNAS-CSIC) was invited to talk about the consequences and restoration measures after the Aznalcóllar mine spill to the Guadiamar River, as well as the results of the investigations which is carried out by IRNAS-CSIC researchers in the Green Corridor (RECARE and RESTECO projects). Soil contamination by heavy metals, such as lead, zinc, cadmium and copper, affects the growth and health of plants, soil organisms and, in general, the ecosystem food web. Soil-plant-microorganism interaction is being investigated in soils with different levels of contamination. The ability of plants and their associated microbes to stabilize heavy metals in the soil (a technique known as phytostabilization) and thus reduce the risk of toxicity in the ecosystem is studied.

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.