Mountain Soil Biodiversity facing trace metal legacy in the context of global change
Doctorat Doctorat complet, Programme Doctoral
Agronomie Ecologie
Institution d'accueil
INP - Institut National Polytechnique de Toulouse
Ecole doctorale
Sciences de l'univers, de l'environnement et de l'espace - ED 173


Because of the short growing season, mountain soils are particularly sensitive to environmental changes such as land use and climate change. In the mountainous French district “Département de l’Aveyron”, the rich mineralogical deposits have generated significant mining activities since the Antiquity, and remobilization of metal within a global change context is expected. Although the release of trace metals (TM) has been investigated from a physicochemical point of view, the impact of legacy trace metals on soil biology is still unknown, particularly the potential impact on soil invertebrates (e.g. earthworms, springtails). Due to their diversity, soil invertebrates contributes to numerous ecosystem services and their presence is essential for good soil functioning (Kibblewhite et al., 2008, Barrios et al., 2007). This study aims to assess the impact of former mining activities on soil health, from a biological perspective, focusing on specific TM where isotopic determination is possible, such as lead, copper and mercury. The work conducted in this thesis will determine (a) the effect of historical soil contamination on the diversity of keystone soil invertebrates: springtails and earthworms, (b) the origins of metals found in their tissues via isotopic tracing, (c) the potential adverse effects of mining legacy, combined with global and local environmental changes, on the proper biological functioning of soils.

Context and Motivation

Several studies on mountain environments, including work in the French Pyrenees (Le Roux et al., 2016, Hansson et al. 2017), has highlighted the high sensitivity of mountain ecosystems to TM contamination likely related to high altitudes that favor atmospheric fallout of distant pollution and contaminants. In addition, the release of TM into the environment is more pronounced in watersheds where former mining activities are abundant. The case study of the department of Aveyron is particularly relevant: first, due to its wide and multiple landscape diversity, and secondly, due to its highly diversified geology and important mineral resources that have been favoured by former mining activities: from the Roman period to the last century.
In addition, the soil quality survey shows that the concentrations of TM in the Aveyron soils exceed the geochemical background more frequently than other French areas (Gis Sol, 2011, Redon et al., 2013). The reasons for these enhances are multifactorial and the numerous former mining activities have probably contributed to this (Cuvier 2015, Cuvier et al., 2016).
Furthermore, soil invertebrates and their diversity (in terms of shapes, sizes, types of reproduction, etc.) participate to many soil functions (e.g. decomposition of organic matter) that contribute themselves to many ecosystem services. Understanding why such an assemblage of invertebrates is found at a given location and a given time is a prerequisite to understand and predict the dynamics of the links between soil invertebrate biodiversity and soil functioning.
A preliminary work is currently conducted by a master student to produce a map of all the mine sites in the studied area. Simultaneously, a soil mapping and inventory is underway and will be available for the PhD researcher, at a scale of 1: 250,000, within the framework of the French GISSOL consortium (

Scientific Objectives

The main objective of the proposed work is to evaluate the impact of former mining activities on soil invertebrates and their diversity. Three main scientific objectives are proposed from local to regional scales.

At a local scale (mining site scale = plot scale)
I. Are the local TM concentrations affecting soil invertebrate communities? To answer this question, we will assess the responds of soil invertebrate taxonomy and functional diversities to local contamination gradients at former mine sites.
II. Do soil invertebrates of different functional profiles present the same levels of vulnerability to soil TM? To answer this question, we plan to shed light on differential bioaccumulation capacities (according to the TM) between functionally different individuals.

At a regional scale (Aveyron)
III. Are past mining activities an environmental filter shaping soil invertebrate communities? In other words, are soil invertebrate communities in mining areas (local scales) the result of a non-random assembly of soil invertebrates from the whole regional pool of soil invertebrates (RPS). The RPS will be established from non-mining sites in the Aveyron region.

At local and regional scales
IV. From the previous objective results, interpretation framework of ecosystem dynamics (links between soil invertebrate community dynamics and potential consequences on ecosystem services) from local scales to global scales in the context of mountain environment will be proposed.

Methodology and Planning

Trace metal isotopes, of for example Pb, Cu and Hg, are particularly relevant to investigate sources and pathways of contamination (El Azzi et al., 2013, Hansson et al., 2017b). All metal characterization of TM will be done on both concentration levels and on the isotopic systems.
The impact of metal contamination on soil invertebrates will be assessed by several approaches, each of them contributing to objectives I to III.
Year 1: for objectives I and II, soil invertebrates will be sampled in one or several former mining sites. The sampling strategy will consist of several transects beginning from the center of mining areas. The final sampling strategy and the number of sampled sites will mainly depend on our preliminary work of mapping and characterizing Aveyron mine sites*. From these samples, in a first step, the taxonomic and functional diversities of keystone invertebrate communities (earthworms and collembolans) will be assessed along TM concentrations gradients. The functional diversity assessment uses functional trait-based approaches. Functional traits are individual characteristics of the organism (morphological, physiological, behavioral or phenological) which, through their links with biological functions, provide a better understanding of the functioning of the ecosystem. In particular, traits thus contribute to a better comprehension and prediction of soil invertebrate responses to environmental changes (Pelosi et al., 2013, Pey et al., 2014). In a second step, the differential bioaccumulation capacities, according to the considered TM, will be assessed between functionally different individuals (Austruy et al., 2017). Functionally individuals mean that individuals have a different functional trait profile. Bioaccumulation capacities will be measured for some functionally different earthworms and springtails using bulk concentrations, isotopic approaches and concentrations.
Year 2: for objective III, a significant number of non-mining sites of the Averyon region will be sampled. This sampling will allow us to assess the regional pool of soil invertebrates (RPS). The sampling strategy will probably consist in 4-5 sampling points in each non-mining sites. For all the above reasons (*) the final sampling strategy and the number of sampled sites will be decided afterwards. Then, by the way of data analysis (null models using a trait-based approach), the RPS and the local communities (obtained in the context of objective I) will be compared. It will assess to which extent former mining activities shape actual communities and can be considered as an environmental filter.
Year 3: for objective IV, the polling of the results of the objectives I to III will allow the PhD to construct a conceptual interpretation framework of ecosystem dynamics (links between soil invertebrate community dynamics and potential consequences on ecosystem services) from local scales to global scales in the context of mountain environment.

Compétences requises

We are seeking a talented young researcher with a master degree in soil science, soil ecology or biogeochemistry. Experience in interdisciplinary work combining geochemistry and biology is desired, strong communication skills in written and spoken English is mandatory. Recommended skills: • data management: database, GIS, statistics • teamwork, fieldwork (physical welfare) • driving licence

Your profile is eligible to apply for the PhD/Doctorate program "Make Our Planet Great Again" if:

- You have a Master's degree or you will pass a Master's degree before August 31, 2018
- You have lived in France for less than 90 days since April 1, 2016
- You are exclusively a foreign national

How to APPLY?

Please send your CV and a letter of motivation to the following contact :

Mots clés

Trace metal legacy Soil biodiversity Former mining Functional traits Mountainous environment Soil contamination

Offre financée

Type de financement
Contrat Doctoral
Montant du financement
1350 € Net / mois


Date limite de candidature 04/05/18

Durée36 mois

Date de démarrage01/09/18

Date de création06/04/18


Niveau de français requisAucun

Niveau d'anglais requisB2 (intermédiaire)


Frais de scolarité annuels400 € / an


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