“The following article comes from the Ecolab – members of the organising team for this year’s International SEGH meeting in Europe. The venue in Toulouse, Southern France promises and exciting and informative series of oral and poster presentations in stunning surroundings in the centre of the city.”
Trace Metals (e.g. Pb, Hg, Cu) are metallic chemical elements in small amounts in natural rocks and soils. However human activities have impacted their biogeochemical cycles through local and global dispersions throughout the world since the beginning of the metallurgy more than 5000 years ago. As some of these trace metals are known to be harmful and can be accumulated in natural environments, it is important to understand the present trace metal inventories in soil.
Our study takes place in the upper valley of Vicdessos (Ariège). This is a mountain catchment situated in the French Pyrenees up to 2600 m above see level. As several places in the whole Pyrenees range, human pressure, variable in time and space, have impacted on the surrounding environment. To be more precise mining and smelting activities (Iron, Ag-Pb Galena), intensive agro-pastoral activities, deforestation are documented for this area at least since the early Middle Ages. These activities have been dispersed metals and contributed to the current contamination of soil, leaving here a chemical legacy. We focus our study on Bassiès valley (photo 1) which is a sub-catchment of the upper-Vicdessos Valley (Cf. map 1). The geomorphological shape of the valley results of glacial erosion of the Bassiès monzogranite basement during the last glacial era. Several lakes and mires are formed in this succession of glacial basins and tills. Since 2009, a human-environment observatory (http://w3.ohmpyr.univ-tlse2.fr/) aims to monitor the evolution of human - environment interactions within this geographic zone. Different projects, from botanical research to economic studies through biogeochemistry, are carried out in this context. The aim is to collect data and integrate them to conduct a transdisciplinary research in changing environment.
This PhD project is involved in such context. The idea is to decipher the different natural and anthropogenic factors influencing trace metals flows and accumulation in the catchment, main objectives are to:
- Understand when and how trace metals inputs occurred in the past, and the relationship with contemporaneous environment (e.g. land use, mining, smelting, etc.)
- Highlight temporal variability and origin of present atmospheric trace metals inputs
- Estimate present inventories and the possible release in the case of environmental changes.
To answer these questions, we aim to set up a spatio-temporal approach using environmental archives and atmospheric deposition monitoring. Several cores of environmental archives (Peat, Lakes...) will be analysed to reconstruct past deposition of trace metals on Bassiès catchment (Photo 3). These results should be compared with other studies (palynology, charcoal) and historical data to discuss their possible relationships and influence of changes in environmental pressure on trace metals inputs. Multi-coring will be applied on the Bassiès site to see intra-variability and a Pyrenean coring transect to discuss spatial variability in the last 200 years. Temporal dynamic of actual trace metal deposition is assessed by means of atmospheric deposition clean collectors (Photo 4) along altitudinal transects and soil solution collectors. We will install passive fog collectors designed to ultra-trace metal occult deposition. Special insight will be the study of lead isotopic composition in deposition, cores and surface mosses transects for better understanding of lead sources.
This PhD project is led by Adrien CLAUSTRES in the EcoLab, a laboratory of functional ecology and environment at the University of Toulouse, France. This project is directed by Gaël LE ROUX and Anne PROBST, CNRS researchers also at EcoLab. (http://www.ecolab.omp.eu/).
Adrien Claustres, EcoLab, University of Toulouse, France