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.


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.

Twenty years of environmental studies in the Guadiamar

The Aznalcóllar mine accident (April 1998) was a large-scale ecological and socio-economic catastrophe in the South of Spain. Since then, the Research Group SOIL-PLANT in the IRNAS, CSIC has been working on the area affected by the mine spill, currently known as Guadiamar Green Corridor.

With the occasion of the 20th anniversary of this environmental catastrophe, a review article has been prepared, including all the studies dealing with soil and plant relationships, carried out within the contaminated and remediated zone of the Guadiamar Green Corridor. This review is a contribution to RESTECO and RECARE projects.

The published information about the chemical composition of the sludge and contaminated soils is reviewed in this article, as well as the monitoring of trace elements and their dynamics in the soil-plant system. The effectiveness of different types of amendments to remediate these soils, at different spatial and time scales, is reviewed. The soil concentrations of trace elements are shown, and their transfer to plants (crops, herbs, shrubs and trees) are evaluated focused on the possible toxicity effects in the food web. The utility of some plant species (accumulators of trace elements) are examined, as biomonitors. Finally, the experience acquired during 20 years of environmental studies in the Guadiamar Green Corridor is discussed, remarking its international relevance as a large-scale phytoremediation of contaminated soils.

The review article is published in the June 2018 issue of the journal Science of the Total Environment.

Madejón P., Domínguez M.T., Madejón E., Cabrera F., Marañón T., Murillo J.M. 2018. Soil-plant relationships and contamination by trace elements: A review of twenty years of experimentation and monitoring after the Aznalcóllar (SW Spain) mine accident. Science of the Total Environment 625, 50–63.

Root functional traits in Mediterranean forests and shrublands

Roots have a fundamental role in plant function (uptake and storage of water and nutrients), as well as in ecosystem properties (primary productivity). Root activities are related with structural traits, such as diameter, density and specific area. However, there are few studies about the importance of functional root traits in Mediterranean environments.

A research team of the IRNAS, CSIC and the RESTECO project, in collaboration with the University of Córdoba, have explored the variation of root traits for 80 woody species (trees and shrubs) along a regional gradient in south Spain, covering from 200 up to 2000 mm of annual rainfall.

In general, strong relationships were found among the root traits. For example, those woody species with higher root specific area had thinner roots and lower tissue density. The main variation trend was interpreted as the “root economics spectrum”. However, the root diameter was not aligned along this main axis. We suggest to study other traits and to explore the existence of multidimensional root traits spectrum.

Soil water and nutrient availability was the main driver of variation among the root traits. Thus, plant communities growing in more productive environments were dominated by those species having root traits associated with rapid acquisition of resources. The foreseen reduction in water availability, caused by climate change, will limit species diversity and modify functioning of forest communities.

This study was published on line (October 23, 2017) in the journal Plant and Soil as part of a monographic issue on root traits.

de la Riva, E.G., Marañón, T., Pérez-Ramos, I.M., Navarro-Fernández, C.M., Olmo, M., Villar, R. (2017). Root traits across environmental gradients in Mediterranean woody communities: are they aligned along the root economics spectrum? Plant and Soil.

On the Journal of Ecology front cover

The most recent issue of the Journal of Ecology (vol. 105, issue 5, September 2017) selected for its front cover our work on climatic variability and functional traits of Doñana shrublands.

As indicated in the Journal´s blog:

“The cover image, taken by Ignacio Pérez-Ramos, shows PhD student Carmen Padilla-Díaz collecting leaves for trait measurements in the Doñana National Park.”

This paper was already posted in the RESTECO project´s blog when it was published on line on February 28, 2017:

The full paper can be consulted on the Journal of Ecology web site:

The front cover image can be also viewed in Pinterest:

Potential of eucalypt trees for remediation of contaminated soils

The use of trees to immobilize contaminants (phytostabilization) is a low-cost and effective method of soil remediation.

Researchers of IRNAS, CSIC and New Zealand have evaluated the potential of red gum (Eucalyptus camaldulensis) to phytostabilize soils contaminated by trace elements (TE). Within the research project RESTECO, the ET concentration in soils and in eucalypt leaves and flowers has been investigated in 7 sites along the Gudiamar River valley. In general, the concentration of elements such as As, Cd, Cu, Pb and Zn in aboveground tissues was relatively low, and lower than toxic levels.

Eucalyptus camaldulensis is a fast-growing tree with a large root system; because of its tolerance to TE contamination and the low transfer of metals towards the aboveground tissues it can be considered suitable for phytoremediation of contaminated soils.

In addition, there was significant correlation between the concentration of Cd, Mn and Zn (but neither for Cu nor Pb) in their leaves and in the rhizosphere. Therefore, the eucalypt´s leaves may serve as bioindicators of the soil contamination for Cd, Mn and Zn.

The study has been published on June 30th 2017 in the open access journal PLOS ONE.

Madejón P, Marañón T, Navarro-Fernández CM, Domínguez MT, Alegre JM, Robinson B, Murillo JM (2017) Potential of Eucalyptus camaldulensis for phytostabilization and biomonitoring of trace-element contaminated soils. PLoS ONE 12(6): e0180240.


Functional diversity and stability against climatic change

The functional diversity of a community is a key factor for its stability against climatic change.

Researchers from RESTECO project, in collaboration with University of Córdoba, Autonomous University of Barcelona and EBD-CSIC, have studied the role of functional diversity and soil conditions as main drivers of the stability of woody plant communities in Doñana (south Spain).

The community stability has been assessed as changes in cover, species composition and diversity, in 19 experimental plots during 9 years. The functional diversity was calculated using eight traits (of leaves, stems and roots) for the 16 species comprising the different communities.

Results have proved that shrubland communities were strongly sensitive to inter-annual variability in climate. During colder and drier conditions, total plant cover decreased remarkably, but functional diversity increased; likely because of the expansion of functionally dissimilar species in the new open microsites.

The most functionally diverse communities, and those inhabiting resource-limited environments were the most stable over time in terms of species diversity. This could be explained because they were mainly constituted by a large diversity of slow-growth, stress-tolerant species that are potentially better adapted to harsh climatic conditions.

We could infer that the increased frequency of extreme climatic events (predicted by climatic models) will alter the functional structure of shrubland communities, with potential repercussions for ecosystem functioning.

This study has been published in the Journal of Ecology (on line since February 28, 2017).

Pérez‐Ramos, I. M., Díaz‐Delgado, R., de la Riva, E. G., Villar, R., Lloret, F., Marañón, T. (2017). Climate variability and community stability in Mediterranean shrublands: the role of functional diversity and soil environment. Journal of Ecology doi: 10.1111/1365-2745.12747

Data can be consulted at the free access DRYAD repository.

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.


Mycorrhization patterns along an environmental gradient

figura_micorrizasMycorrhizal symbiosis is a mutualist association between plants and fungi which may be critical under stressful environmental conditions, like in Mediterranean forests constrained by water stress and resource scarcity.

Researchers of the IRNAS-CSIC and the University of Córdoba have studied how the degrees of colonization by ectomycorrhizal (ECM) and arbuscular mycorrhizal (AM) fungi were related to other root and leaf traits, in woody plant communities of Sierra Morena (Córdoba) distributed along a gradient of soil resources.

The level of ECM colonization was positively related to the abundance of evergreen species and to tissue dry matter content (in leaves and roots), but negatively to specific root length and specific leaf area. The best abiotic predictor of ECM colonization was soil moisture, with higher ECM colonization in drier sites.

However, AM colonization was not related to any of the plant traits studied and was positively related to soil Cu and other physico-chemical soil properties.

Changes in community ECM mycorrhization were primarily due to plant species turnover, while in the case of AM colonization was more important the intraspecific variability.

The proposed mycorrhizal trait-based approach is novel and useful to understand the functioning of Mediterranean forests and shrublands.

The study has been published (on line since August 29 2016) in the Journal of Vegetation Science.

Navarro-Fernández CM, Pérez-Ramos IM, de la Riva EG, Vera JR, Roumet C, Villar R, Marañón T (2016). Functional responses of Mediterranean plant communities to soil resource heterogeneity: a mycorrhizal trait-based approach. Journal of Vegetation Science, DOI: 10.1111/jvs.12446.

Evaluation of forest ecosystem services in Andalusia (S Spain)

Castanea IstanForests are suppliers of important ecosystem services, provisioning (timber, foods, resins), regulating (improving air and water quality, soil protection, carbon sequestration) and cultural (recreation, aesthetic, spiritual) contributing to human well-being.

Researchers of the IRNAS, CSIC and EVENOR-TECH have evaluated the state and trends of ecosystem services provided by the forests of Andalusia (S Spain). In particular, changes during the last 50 years have been analysed for two main regulating services: soil protection from erosion and capacity of carbon storage.

In general Andalusian forests have increased their carbon storage by 3040 Gg C during the last 50 years, due to the plantations of conifers and eucalyptus. While the soil erosion risk has increased because the area of open spaces, deforested or burnt has tripled.

This study has been published in the August 2016 issue of the journal Ecosystem Services.

Anaya-Romero M, M Muñoz-Rojas, B Ibáñez y T. Marañón. Evaluation of forest ecosystem services in Mediterranean areas. Ecosystem Services 20: 82-90.