The fate of polluted ecosystems: temporal dynamics of small mammal abundance and their exposure to toxic metals around a former industrial site

M2 internship – 02/02 to 01/08/2026 – Besançon

What are the ecological trajectories of polluted ecosystems? Do recovery and resilience processes operate in these disturbed systems? Are these phenomena spatially heterogeneous within polluted sites? These research questions have scarcely been addressed, partly because they require long-term monitoring to understand the fate of contaminants within the critical zone and to inform the dynamics of animal populations. At the Harjavalta site in Finland, Eeva & Lehikoinen (2000) demonstrated a decrease in lead (Pb) exposure and an improvement in reproductive success in two species of insectivorous passerines, the great tit (Parus major) and the pied flycatcher (Ficedula hypoleuca), following a reduction in atmospheric emissions from a smelter, thus demonstrating a recovery in these bird populations. However, toxic trace metals (TMs) such as Pb and cadmium (Cd) are persistent, and soil contamination leads to long-term chronic exposure of flora and fauna and transfers within food webs, with associated risks in terms of deleterious biological and ecological effects. Besides, the aging of pollutants in soil could reduce the bioavailability of metals, thereby reducing exposure of the organisms. Chrono-environnement has been studying the transfer of TMs in food webs and their impact on the Metaleurop Nord site since 2006. This monitoring provides an opportunity to study the long-term, large-scale fate of a heavily contaminated ecosystem and to explore the underlying mechanisms. Time series data from these long-term surveys can be fit to statistical models (N-mixture models) that take imperfect detection into account (Royle 2004), and the resulting abundance estimates can be used to identify the role of TMs in driving population dynamics.

The study aims to explore and understand temporal trends (1) in exposure of small mammals to toxic metals based on bioaccumulation in organs and (2) in small mammal population dynamics across different areas representing a soil pollution gradient over the Metaleurop Nord site.

The work is divided into two complementary parts: (1) numerical and statistical analysis of available data on the abundance of individuals and bioaccumulation in small mammals, and (2) participation in the preparation and implementation of the annual field monitoring session.

Desired skills: Data management, data processing, numerical and statistical analysis, GIS, background knowledge in ecology and ecotoxicology, field skills and experience handling wildlife, rigorousness, ability for team work, autonomy. Students should be comfortable with programming in R and have a strong working knowledge of probability distributions and generalized linear models. The project will use Bayesian statistics, and presents an opportunity for applied statistical modelling in R and Stan.