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.

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.

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.