Graduate Thesis on phytostabilization and soil organic matter

Trees planted in contaminated soils provide organic matter, contributing to a reduced mobility of contaminants and the process called “phytostabilization”.

Within the collaboration between IRNAS, CSIC and the University of Seville, Juan Fernando Montero supervised by the RESTECO researcher María T. Domínguez, has presented in July 2018, in the Faculty of Chemistry, the Graduate Thesis titled “Caracterizing fractions of organic carbon in forested soils after the Aznalcóllar mine accident (Guadiamar Green Corridor)”.

In this study, several fractions of soil organic carbon were analyzed, comparing sites under different tree species (white poplar, stone pine and wild olive). The study was repeated in two contrasted areas, with different soil acidity levels.

Using Fourier-transform infrared spectroscopy (FTIR), functional groups were caracterized in samples of soil and litter. The spectra of soil samples differed from those of litter, especially when the soil was neutral to basic, due to the higher intensity of microbial acitivity and litter decomposition in those sites.

Presentation in the Iberian Congress of Soil Science

“The soil as sustainable resource for the bioeconomy” was the theme for the VIII Iberian Congress of Soil Sciences, held at San Sebastián/Donosti, during 20-22 June 2018.

Researchers of the projects RECARE and RESTECO contributed to the 3rd session, devoted to “Protection and restoration of soils”, with the comunication titled “Soil restoration strategies in the Guadiamar River Valley. Evaluation of 20 year of monitoring after the Aznalcóllar mining accident”.

This work is a review of the 20-year monitoring of contaminated and remediated soils, after the Aznalcóllar mine-spill. The application of soil amendments (sugarbeet lime and biosolid compost) was evaluated and results of 14-year changes of pH and organic carbon were shown.

At a large scale, in a soil survey along the Agrio and Guadiamar rivers, high level of Cd and Zn were detected in certain spots of channel and river banks.

A copy of the presented poster can be downloaded from Digital CSIC.

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.

Workshop on ecosystem services

Ecosystem services are the direct and indirect contributions of ecosystems to the human wellbeing. The remediation of contaminated soils after the Aznalcóllar mine spill, and the restoration of the Guadiamar Green Corridor (Sevilla, Spain) provide with multiple ecosystem services to local and regional societies.

The stakeholder workshop for the evaluation of ecosystem services was held on November 29th 2017. Benefits arisen from the implementation of two remediation measures – amendment addition and tree plantations – were valuated by stakeholders.

This workshop was organized by the IRNAS, CSIC and Evenor Tech, in the Guadiamar Visitor Centre at Aznalcázar, Sevilla, thanks to the collaboration of Guadiamar Educa. It was part of the projects RECARE and RESTECO.

Stakeholders valuated mainly the benefits associated to regulation services, such as stabilization of contaminants, soil formation and mitigation of climate change by carbon sequestration. They also valuated highly the cultural services related with recreational activities, ecotourism, landscape value and the scientific interest as natural laboratory for environmental research. Lastly, some provisioning services were valuated, like production of biofuel and of forage for horses.

The workshop presentations and the Report with the results will be uploaded at the communication platform Recare-hub.

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.

Contribution to Soil Organic Matter course

Under the current situation of climate change, the carbon storage in terrestrial ecosystems, particularly in forest soils, becomes very relevant for the mitigation of the increasing CO2 in the atmosphere and the reduction of global warming.

A conference about “The soil and organic matter in ecosystem services provision” has been delivered. After the general introduction of the concept “ecosystem services”, the importance of the regulation service associated to the soil carbon storage for the mitigation of climate change was explained. Examples of the projects RECARE and RESTECO were used to illustrate the importance of soil and its ecosystem services.

The conference was part of the Course “Soil organic matter: methods for analysis, and incidence on the environment and climate change”, coordinated by José María de la Rosa Arranz, held in the IRNAS, CSIC, Seville (Spain), during 16-19 Octobre 2017.

A pdf copy of the conference presentation can be downloaded from Digital CSIC.

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:

Plant functional traits and ecosystem properties

Plant traits resulting from evolutionary and physiological processes have produced a global and extraordinary functional diversity among the myriad of species colonizing contrasted habitats within the planet Earth.

Trait-based ecology helps us to understand better the community assemblage, ecosystem function and the responses to environmental changes.

Researchers of the RESTECO project and the Córdoba University have participated in the Symposium “Trait covariation: structural and functional relationships in plant ecology”, at Exeter (UK) during 27-29 June 2017.

Two comunications were presented:

1) Functional traits of trees affect soil properties and provision of ecosystem services. A study of seven tree species planted on remediated soils in the Guadiamar Green Corridor (Seville, Spain) has shown significant differences in traits (SLA, SRL, LDMC, RMDC) and chemical composition of leaves and roots. These traits differences influence the tree capacity to immobilize contaminants (trace elements) into the soil, remediation technique called phytostabilization. Traits also influence tree capacity to store carbon into biomass and soil, therefore contributing to climate change mitigation.

2) Within plant traits, roots are little known, despite their crucial role in the plant strategies of resource use and the ecosytem funcioning. Variation patterns of 5 root traits in 80 woody plant species from 18 samplig sites and 5 zones of South Spain have been studied. A strong correlation among traits indicates a main dimension along the root economics spectrum. However, other dimensions such as root diameter and the association with mycorrhizal fungi are also relevant.

The abstract and copy of the poster can be consulted in Digital CSIC repository:

Marañón et al. (2017) Traits influence the role of trees on ecosystem services: phytostabilization of trace elements and carbon sequestration.

Villar at al. (2017) Root traits across environmental gradients in Mediterranean woody communities: are they aligned along a single acquisition-conservation axis?