MACROTOX - Impact of toxic chemical pressure on the current evolution of macroinvertebrate communities in French watercourses

Objectives

The overall objective of this PhD is to characterize the specific effects of chemical contamination on the diversity of macroinvertebrates in French national rivers by comparing taxonomic monitoring data from surveillance networks with in situ ecotoxicology indicators derived from active biomonitoring. These new indicators quantify exposure to different substances as well as the toxicity of the environmental mixture. This main goal is divided into several specific objectives:

1. Identify national-scale taxonomic patterns associated with chemical contamination according to the type of pressure (agricultural, urban, industrial, natural).
2. Examine the influence of contextual factors (geographical, climatic, etc.) on these response patterns to chemical pressure and identify possible interactions in order to explain the observed territorial differences.
3. Reassess the impact of chemical pressure, in light of the spatial results from points 1 and 2, on the temporal trends of invertebrate communities at observatory sites involved in the long-term monitoring of the effects of the Rhône River ecological restoration.
4. Explore the community processes (erosion, replacement, homogenization) underlying the regional structuration of communities along gradients of chemical pressure.
5. Provide a functional interpretation of the observed taxonomic changes and identify biological traits selected or counter-selected in response to chemical pressure.
6. Assess whether these functional changes lead to shifts in community vulnerability to other pressures affecting aquatic ecosystems.

Approaches

This work seizes the recent opportunity to combine taxonomic monitoring data collected over the past 20 years within national surveillance networks with in situ ecotoxicological indicators (caged gammarids), repeatedly sampled at several hundred sites over the last five years.

These two types of data, complemented by various environmental variables, will be analyzed using different statistical modeling approaches at multiple scales (national, hydro-ecoregions, watersheds). In a first step, the goal is to figure out changes in macroinvertebrate communities (richness, abundance, composition) attributable to different types of chemical pressures (agricultural, industrial, urban, etc.), while accounting for environmental context.

This knowledge will then be used to better understand the diversity of dynamics observed locally within the Rhône hydrosystem through the macroinvertebrate monitoring data collected during restoration activities carried out as part of the RhônEco program.

In a second step, beta-diversity metrics will also be examined to disentangle the processes of regional structuring (species turnover, homogenization) associated with chemical pressure.

Finally, an approach based on species bio-ecological traits will translate taxonomic changes in terms of functional diversity in order to better understand the influence and direction of selective pressures acting on these traits and, ultimately, on the functional structure and composition of communities (e.g., assessment of the degree of functional redundancy). The hypothesis that sensitive species are replaced by functionally equivalent tolerant species will be tested, and stress sensitivity values (thermal, chemical, etc.) will be used to assess the potential vulnerability of communities to environmental change.

Contacts

Arnaud Chaumot (RiverLy)

David Eme (RiverLy)

Jeanne Thill (RiverLy)