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The Aznalcóllar mine accident (Seville), in April 1998, was an ecological and socioeconomic catastrophe with important international impact. The remediation and restoration of the area affected by the mine spill transformed a devastated and contaminated area into the current Guadiamar Green Corridor Protected Landscape. Despite the successful recovery of the affected area, residual contamination is still present.

One of the main threats from the mine spill was the presence of potentially toxic trace elements, such as As, Cd, Pb and Tl, in the contaminated soil. Therefore, it exists a risk of toxicity due to their possible transfer from the soil to the food chain, since the contents of these elements at high concentrations can be harmful to livestock and wild animals, as well as to human health. A research team of the IRNAS-CSIC led by José Manuel Murillo, in collaboration with the researchers Paula Madejón, María Teresa Domínguez and Engracia Madejón, has published the book chapter entitled “Risks for the food chain in the Guadiamar Green Corridor”. In this chapter, most of the studies carried out in the Green Corridor, dealing with the transfer of trace elements at different levels within the food chain, during the 20 years since the accident are collected. In addition, the corresponding potential risks of toxicity for animals and for human consumption are evaluated.

Horse grazing in the Guadiamar Green Corridor (photo by M.T. Domínguez).

Three relevant case studies, conducted by IRNAS researchers, are described in more detail: the potential toxic effect on the horses that graze in the Green Corridor, the accumulation of trace elements in land snails, and the transfer and accumulation of these elements in mushrooms. Both snails and mushrooms are wild foods that can be collected in the Green Corridor and consumed by local residents.

Finally, it is clearly explained why the neighbours of the close villages of the Green Corridor must not collect any food product from the contaminated area, for human consumption.


Madejón P, Madejón E, Domínguez MT, Murillo JM (2020). Riesgos para la cadena trófica en el Corredor Verde del Guadiamar. In: P Madejón y T Marañón (eds.), Recuperación de suelos y provisión de servicios ecosistémicos en el Corredor Verde del Guadiamar, pp. 113-135. Editorial CSIC, Madrid.

The mine tailing accident occurring on April 1998 at Aznalcóllar (Seville, Spain) was a great ecological and socioeconomical disaster, with international impact. The remediation and restoration of that spill-affected area transformed a devastated and contaminated land into the current Protected Landscape of the Guadiamar Green Corridor.   

The Research Conference of the XX Anniversary of the Aznalcóllar Mine Accident was organized on April 2018 in the IRNAS-CSIC, Seville, as part of the transfer activities of the INTARSU project. Based on that Conference, the Editorial CSIC has published on July 2020 the book “Soil remediation and provision of ecosystem services in the Guadiamar Green Corridor” (in Spanish), edited by the INTARSU researchers Paula Madejón and Teodoro Marañón.

The final chapter of the book gathers the main topics raised during the roundtable which closed the meeting. In particular, the participants identified and discussed the main challenges and opportunities after the mine accident.    

The environmental disaster was a great challenge for the natural ecosystems within the Guadiamar Basin and for the economy of the affected area. Among the short-term challenges, it was priority the urgent cleaning and remediation of the polluted soils. At long-term, it was essential to maintain the monitoring and vigilance of the potentially toxic elements in the ecosystem. It was a relevant challenge to transmit to the local people that the toxicity risks were, although mitigated, still present and for long-term in the spill-affected area. From the conservationist perspective, the main challenge on middle- and long-term, was to consolidate the ecological corridor connecting Doñana and Sierra Morena; that ecological function should be compatible with the multiple use of the Protected Landscape. Looking at the future, a worrying challenge is the reopening of the mine; their activities must be compatible with the maintenance of environmental quality and healthy ecosystems. Finally, a pending challenge was remarked: to enforce the “polluter pays principle”.

Roundtable participants; from the left to the right, Teodoro Marañón (moderator), Miguel Ferrer, Emilio Galán, Paula Madejón, Francisco Cabrera, María Teresa Domínguez and Francisco Quirós.

At the same time, the recovery of the mine accident offered also new opportunities. The most relevant opportunity was the strong support to the environmental scientific research, in particular to fields like the remediation of soils contaminated by trace elements, and to the evaluation of potential toxicity of contaminants on plants and animals. The Guadiamar Green Corridor has been a large-scale natural laboratory where several remediation measures have been tested, and where the dynamics of trace elements have been monitored. For the conservationists, it was a real opportunity to have a privileged protected space (the Guadiamar river) able to connect the isolated populations of Doñana with the large populations of Sierra Morena. This newly protected area is also an opportunity to practice recreational activities and ecotourism. It was suggested as future opportunity for the Aznalcóllar mine, to develop new, cleaner technologies and more reliable exploitation systems.       


Marañón, T. (2020). Challenges and opportunities after the Aznalcóllar´s environmental disaster. In: P. Madejón and T. Marañón (eds.). Soil remediation and provision of ecosystem services in the Guadiamar Green Corridor, pp. 195-206. Editorial CSIC, Madrid (in Spanish).

ISBN: 978-84-00-10636-2

Root functions are multiple and essential for plant growth and survival. They include nutrient and water acquisition, resource storage, support of symbiotic soil microbes and anchorage. At the ecosystem level, they contribute to soil structure and to the carbon and nutrient cycles.

Researchers of the IRNAS-CSIC, in collaboration with the University of Seville and the University of Cordoba, have studied the variation of 27 root traits (morphological, chemical and isotopic) in seven tree species planted in the Guadiamar Green Corridor (Seville, Spain). Three of the species are deciduous: white poplar (Populus alba), narrow-leafed ash (Fraxinus angustifolia) and hackberry (Celtis autralis). While the other four species are evergreen: stone pine (Pinus pinea), holm oak (Quercus ilex), wild olive (Olea europaea) and carob (Ceratonia siliqua).

The main variation trend observed in the root traits supports the “root economics spectrum” hypothesis. There is a trade-off between tree species having lighter roots and higher length per mass unit, which maximizes soil resource acquisition and thus they grow faster on favourable conditions. On the contrary, tree species with denser roots and lower specific length tend to have resource conservation and slower growth, on adverse conditions.

Besides the main trend, there are other dimensions reflecting the root multifunctionality. 1) The root carbon concentration was not correlated with the morphological variables. 2) the ability to bind trace elements (for example, Pb and Cd) to root cells tends to be associated with the plant tolerance to soil contamination by metals. 3) The fractionation of 15N in roots is a time-integrated trait of mycorrhizal mediated nutrition.

In general, roots and leaves are functionally coordinated. The fast acquisition and processing of water and nutrients by the roots must be coupled with fast acquisition and processing of carbon by leaves. However, there was strong discordance between roots and leaves, with regards to the accumulation of several trace elements.

Soil conditions, and metal contamination in particular, affect morphological and chemical traits of tree roots. There are reciprocal interactions and feedback processes between soil and tree roots.

A remarkable physiological trait for these tree roots is the capacity to diminish the availability of trace elements into the soil, in special of those potentially toxic (Cd, Pb, As). We recommend planting trees with high “phytostabilisation” potential to remediate metal-contaminated soils.

This study has been published in the April issue of the journal Plant and Soil:

Marañón, T., Navarro-Fernández, C. M., Gil-Martínez, M., Domínguez, M. T., Madejón, P., Villar, R. (2020). Variation in morphological and chemical traits of Mediterranean tree roots: linkage with leaf traits and soil conditions. Plant and Soil, 449: 389-403.

Interactions between plants and soil are responsible for providing numerous ecosystem services from forests, including carbon sequestration, protection from erosion, improved soil fertility and stabilization of contaminants.

In the XXV World Congress of the IUFRO (International Union of Forest Research Organizations), held at Curitiba, Brasil from September 29th to October 5th, a scientific session (number E8,d,g) was devoted to the topic “Plant-soil interactions in forests”.

1) Different tree species affect differently to soil properties. For example, soil pH underneath pines (Pinus pinea) and holm oaks (Quercus ilex) was lower than under other five tree species in the same study area. These soil pH differences have relevant consequences for the mobility of trace elements and their uptake by trees (Madejón et al., 2018, Catena 166: 34-43).

2) Soil mycobiota differed in diversity and composition under wild olive (Olea europaea), stone pine (Pinus pinea) and white poplar (Populus alba), and with adjacent treeless sites. The afforestation represented 100% increase of soil fungal diversity, compared with the remediated zones (only with pastures). A total of 6535 OTUs (operational taxonomic units) were estimated as the gamma diversity of soil fungi in the study area (Gil-Martínez et al., in preparation).

The functional diversity of soil fungi (according to the FUNGuild data base) was represented by three main functional groups: saprotrophs (68% of OTUs), pathogens/parasites (18%) and mycorrhizal fungi (12%). Within the mycorrhizal fungi group, arbuscular fungi were associated to soil samples under wild olive and treeless pastures, while ectomycorrhizal fungi were abundant in soil under poplar and pine.

3) The case of mycorrhizal fungi is relevant because of their symbiotic relations with trees. Ectomycorrhizal fungi communities were studied by sampling root tips of 40 holm oaks (Q. ilex) distributed along four sites of the Guadiamar Green Corridor. A total of 55 OTUs were identified, with average of 3.8 fungal species per tree. Soil properties influencing primarily the composition of mycorrhizal fungal communities were total soil carbon, and the concentration of Ca, Cu, Ni and Zn (López-García et al., 2018, Soil Biol Biochem 121: 202-211).

In turn, the composition of mycorrhizal fungal communities affected significantly the accumulation of P in leaves, and the transfer rate of Zn from soil to root (Gil-Martínez et al., 2018, Front Plant Sci : 1682).

4) Soil fungi have a relevant role degrading organic matter and cycling nutrients, by the action of extracellular enzymes. We have found that beta-glucosidase activity (enzyme contributing to cellulose degradation) was much higher in the soil under poplar and pines than in soil under wild olive or in pastures. A feedback process can be inferred, by which tree species influence composition and abundance of soil fungi, and the rate of enzyme activity, which in turn promote organic matter decomposition and release of nutrients, which are up-taken by trees (Gil-Martínez et al., 2018, Proceed. Mine Closure 2018, Leipzig, pp. 636-647).

In summary, there are complex interactions between the aboveground and belowground subsystems of the forest ecosystem. Several examples of tree-microbiota-soil feedback processes have been studied in the Guadiamar Green Corridor. Metal uptake by trees is influenced by soil pH, which in turn can be modified by litter decomposition and root exudates. The composition and diversity of soil fungi are affected by tree species identity; on the other hand, mycorrhizal fungal communities influence some tree processes, like leaf P concentration, and Zn transfer from soil to root. Trees influence on soil enzyme activities, which in turn affect nutrient cycling and their uptake by trees.

A pdf copy of the presentation slides can be consulted in Digital CSIC.

The XXXII Reunión Nacional de Suelos organized by researchers from the field of edaphology belonging to the University of Seville and the Institute of Natural Resources and Agrobiology of Seville (IRNAS-CSIC) took place in Seville (Spain) on 10-13 September 2019. This meeting is an initiative of the Spanish Society of Soil Science (SECS) that has been taking place since 1973 as they organize excursions to get to know different Spanish soils.

The meeting began with a session of posters and presentations framed within different themes (see Abstracts Book). Within the theme of “Study and recovery of contaminated soils” Marta Gil Martínez, predoctoral researcher at IRNAS-CSIC, presented a study on the fungal functional diversity in trace element contaminated soils from the Guadiamar Green Corridor.

In this study, the soil fungal communities were analyzed with a methodology of next generation sequencing in soils with different levels of contamination by trace elements and with different plant covers. The results showed that the phytoremediation plan established after the Aznalcóllar mining accident has favored the development of fungal communities by increasing their species richness and diversity. Both the type of vegetation covers and the properties of the soil determine the structure of the fungal communities. Under the poplar and pine trees, the communities of ectomycorrhizal fungi dominate, and under the wild olive and herbaceous species dominate arbuscular mycorrhizal fungi, due to the specific symbiosis of each type of vegetation with the fungi.

Access to the poster in this link:

Gil-Martínez M, López-García Á, Navarro-Fernández CM, Domínguez MT, Marañón T (2019). Fungal functional diversity in trace element contaminated soils from the Guadiamar Green Corridor. XXXII Reunión Nacional de Suelos (Seville).

In the following days we made three diverse and representative itineraries of the main soils and landscapes of Western Andalusia: 1) a protected and unique space in Europe, Doñana National Park; 2) a global example of restoration such as the Guadiamar Green Corridor, a protected area after the Aznalcóllar mining disaster, and finally 3) the Mediterranean soils of the valley and countryside of Carmona.

In the Doñana National Park, the researcher Luis Clemente (IRNAS-CSIC) explained the types of soils and the various ecosystems that Doñana include. In the Guadiamar Green Corridor we visited the Aznalcóllar mine and the researchers María Teresa Domínguez (University of Seville) and Engracia Madejón (IRNAS-CSIC) explained the details of the accident and the studies that have been carried out since then. In Carmona, we study two soil profiles with the help of Antonio Jordán (University of Seville).


This past June, from 23-28, the 8th International Symposium on Interactions of Soil Minerals with Organic Components and Microorganisms was held in the city of Seville. This symposium was organized by Division 2.5 belonging to the International Union of Soil Sciences (IUSS). The specific theme chosen for this symposium was “Understanding Soil Interfacial Reactions for Sustainable Soil Management and Climate Change Mitigation”.

From the INTARSU Project we had the opportunity to participate in this symposium in the scientific session entitled “Dynamics of pollutants at soil interfaces – What is new and how can environmental biotechnology be beneficial for soil restoration and bioremediation?”

Marta Gil Martínez gave an oral presentation entitled “Tree species effect on soil organic matter and soil microorganisms in trace element contaminated soils” where she presented the latest results obtained from the study about the effects of phytoremediation in soils contaminated by trace elements, after the mining spill of Aznacólllar in 1998. In this study, an exhaustive study of the changes in soil organic matter was carried out under three tree species: olive, white poplar and pine, and in a treeless area dominated by herbaceous species. In addition, two zones located 15 and 30 km from the discharge point were sampled to study, as well as, how the effects of these trees vary according to the physical and chemical properties of the soils.

The objectives of this study were:

- Evaluating the effect of these species on different fractions of soil organic matter, after 15 years of tree growth, as part of the phytoremediation program.

- Analysing the influence of microbial activity in two contrasted areas with different degradation status.

The results obtained from this study showed that the North zone (closer to the mine) has greater availability of trace elements due to the acidic pH and the low content of soil organic matter. Among the species studied, the pine had an acidifying effect in this zone but not in the South zone (farther from the mine) due to the neutral pH and greater buffering power of these soils. This effect of the pine is explained by infrared analysis, which showed its litter and underneath soils some characteristic peaks of acidic functional groups (pectins, resins and waxes), which did not appear in other species infrared analysis.

The effects of phytoremediation had a positive effect on the amount of organic matter, compared to treeless areas, and this was reflected in a greater microbial biomass.

Among the conclusions of this study, we highlight the potential of pine trees to acidify the soil, however this species also generates a large amount of litter, increasing the organic matter of the soil. It has also been found that reforestation has increased microbial biomass, therefore, new functionalities are being recovered in soils.

You can access the presentation in this link:

Gil-Martínez M, Fernández Boy ME, Marañón T, Montero González JF, Navarro-Fernández CM, Domínguez MT (2019). Tree species effect on soil organic matter and soil microorganisms in trace element contaminated soils. 8th International Symposium on Interactions of Soil Minerals with Organic Components and Microorganisms (Sevilla).

The Iberian Ecological Society SIBECOL has just been established to gather professional scientist from Portugal and Spain from all ecology areas: theoretical, terrestrial, marine and continental waters. Its main aim is promoting ecology and to give visibility to scientific works in all these fields.

To celebrate the establishment of the society and to share the scientific progress in ecology, last 4th -7th of February the First SIBECOL Congress, as well as the XIV AEET Meeting, were celebrated. The venue selected was the Faculty of Biology at the University of Barcelona (Spain).

This congress was celebrated in an emblematic time and place due to the commemoration, this year 2019, of the centenary of Professor Ramon Margalef. Margalef became one of the most relevant ecologist of the XX century and the first professor of Ecology in Spain at the University of Barcelona, where all the Iberian ecologist had the opportunity to meet.

INTARSU Project did not want to miss this important event for ecology and we had the opportunity of presenting our last study in a poster titled: “Phytostabilisation of trace elements with different tree species revealed a species-specific effect on soil functioning”. This work has been possible thanks to the collaboration between researchers from IRNAS-CSIC, University of Sevilla and University of Reading (United Kingdom). The poster was presented in the Thematic Session 14 “Organisms and ecosystem responses to global change in soils and sediments”, organized by the Group of Plant-Soil Interactions of AEET.

In this study, we presented the effects of different tree species (white poplar, wild olive and stone pine) on biotic and abiotic soil properties. The study area, known as Guadiamar Green Corridor (Seville), suffered in 1998 a serious contamination due to Aznalcóllar mine-spill. After a remediation plan in the whole affected area, different tree and shrubs species were planted, and 15 years after these trees have generated soil changes. In relation to soil nutrients, we have found that the tree coverage has increased fertility in soils underneath compared to soils covered by herbaceous plants. Among the studied species, white poplar trees have helped to neutralize soil pH; however, stone pine trees have acidified the soil which is undesirable as acidity increases soil trace element availability. Soil microbial activity presented differences among tree species and we found that enzyme activities with an important role in C, N and P cycles were highly dependent on soil pH. To summarise, we have found a tree species effect on abiotic and biotic soil properties with direct consequences on soil functioning.

Gil-Martínez, Marta; Domínguez, María Teresa; Navarro-Fernández, Carmen María; Tibbett, Mark; Marañón, Teodoro (2019). Phytostabilisation of trace elements with different tree species revealed a species-specific effect on soil functioning. In: Abstract book. 1st Meeting of the Iberian Ecological Society & XIV AEET Meeting. Ecology: an integrative science in the Anthropocene. February 4-7, 2019, Barcelona (Spain), page 269. AEET, Madrid, DOI: 10.7818/SIBECOLandAEETmeeting.2019.

The assessment and evaluation of ecosystem services is a valuable tool to support and justify sustainble soil management.

Researchers of IRNAS, CSIC have contributed to the development of a methodology to quantify changes in ecosystem services induced by soil management measures, as part of the European RECARE consortium.

A comparative analysis of the results for 26 measures applied to remediate degraded soils, in 16 case studies across Europe, has been carried out. In particular, IRNAS´s researchers have evaluated the results of amendments (biosolid compost) and tree planting (wild olive) in contaminated and remediated soils of the Guadiamar Green Corridor.

The new methodology was applied to evaluate the impacts of each 26 measures on different ecosystem services. The most relevant 15 ecosystem services were selected, grouped in provisioning, regulation and cultural services. In general, the applied soil remediation measures produced positive changes in ecosystem services. Within the regulation services, “mediation of flows” (protection from erosion) and “mediation of waste, toxics and other nuisances” (stabilization of contaminants) showed the most important positive impacts.

The methodology also detected synergies and trade-offs among ecosystem services. This holistic approach may be the base for a valuation of the benefits from each ecosystem service and the integrated management of the evaluated land.

The results have been published in the December issue of the open access journal Sustainability:

Gudrun Schwilch, Tatenda Lemann, Örjan Berglund, Carlo Camarotto, Artemi Cerdà, Ioannis N. Daliakopoulos, Silvia Kohnová, Dominika Krzeminska, Teodoro Marañón, René Rietra, Grzegorz Siebielec, Johann Thorsson, Mark Tibbett, Sandra Valente, Hedwig van Delden, Jan van den Akker, Simone Verzandvoort, Nicoleta Olimpia Vrînceanu, Christos Zoumides, Rudi Hessel (2018), Assessing impacts of soil management measures on Ecosystem Services. Sustainability, 10 (12), 4416, doi:10.3390/su10124416.

Soil abiotic properties, such as texture, nutrient availability and water, are essential in the development of terrestrial plants. Mycorrhizal fungi, which are fungi living in symbiosis with plants roots, are also key for plant growing. This symbiosis enhances a trade-off of carbohydrates and nutrients beneficial for both plant and fungi. Therefore, it is expected that different mycorrhizal fungal communities (in terms of species and their morphological traits) would affect plant development (in terms of plant chemical and morphological traits) in different ways.

In order to understand this mycorrhizal fungi-plant relationship, researchers from IRNAS-CSIC and Universidad de Sevilla (Spain), in collaboration with researchers from the University of Copenhagen (Denmark) and the University of Reading (United Kingdom), developed a study on holm oak trees and their symbiotic ectomycorrhizal fungi. The area selected for this study, known as the Guadiamar Green Corridor (Seville), suffered a mine spill leaving behind hectares of land contaminated by trace elements. Twenty years after the accident and the phytoremediation of the affected area, trace elements are still present and the role of ectomycorrhizal fungi might be especially important in this stressful environment.

In this study, we found that ectomycorrhizal fungi explained more than soil abiotic properties for most of the measured plant traits, especially root functional traits. The symbiosis with abundant species of ectomycorrhizal fungi (Hebeloma cavipes and Thelephora terrestris) was related to conservative positions into the root economics spectrum. Conservative traits, like denser roots and higher dry matter content, allow tree survival under adverse conditions. Hebeloma cavipes and Thelephora terrestris were characterised with a high rhizomorph formation, a fungal trait that enhances water and phosphate uptake through a long-distance exploration mechanism. It may be possible that this specific tree-fungi symbiosis was established as a consequence of resource limitations.

Trace element mobility through the soil-root-leaf continuum was analysed and despite soil trace elements concentrations in our environmental gradient was relatively large, accumulation of trace elements in oak leaves was relatively low. This confirms that holm oak is a suitable species for the phytostabilisation of contaminated soils, given its ability to prevent trace element accumulation into aboveground biomass. However, it is not the role of the tree alone, as trace element transfer was highly explained by its associated ectomycorrhizal fungal communities, which suggests that interactions with fungi play an important role at determining the capacity of this tree species to retain trace elements into its roots.

These findings support that ectomycorrhizal fungal community composition and their functional traits mediate plant performance in trace element contaminated soils, and have a high influence on plant capacity for phytoremediation of contaminants.

The study has been published in the journal Frontiers in Plant Science:

Gil-Martínez, M., López-García, Á., Domínguez, M. T., Navarro-Fernández, C. M., Kjøller, R., Tibbett, M., & Marañón, T. (2018). Ectomycorrhizal Fungal Communities and Their Functional Traits Mediate Plant–Soil Interactions in Trace Element Contaminated Soils. Frontiers in Plant Science, 9, 1682. 

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.