Biomonitoring

Effect of dams on animal and plant communities in the Selune

Coordinator(s)

Christophe Piscart

Scientific context

The construction of dams on the Selune has created obstacles to the flow of water and materials and disrupted exchanges between upstream and downstream areas. In addition, the formation of large expanses of water behind the dams led to the accumulation of silt at the bottom of the reservoirs and a significant slowdown in the current. All these events have profoundly altered:

• Habitat quality,
• The distribution of animal and plant communities,
• The ecological quality of the environment (accumulation of heavy metals in the silt and proliferation of cyanobacteria in summer)

Communities of aquatic invertebrates (larvae, insects) and primary producers such as plankton and aquatic plants are particularly sensitive to these changes. These communities are distributed in watercourses according to the speed of the current, the quality of the substrate and the food available. Their position at the base of the food chain also makes them important for the stability of ecosystems.

Subject(s) of study

This project focuses on aquatic animal and plant communities: zooplankton, macroinvertebrates, phytoplankton, periphyton and macrophytes.

Objectives

The aim is to assess the impact of dams on communities of aquatic invertebrates and primary producers (phytoplankton, periphyton, macrophytes) by monitoring their evolution (species richness and quantitative analysis).

The research developed as part of this project aim at defining the initial state of these communities in the presence of dams and reservoirs, in order to provide answers to the following questions after their removal:

• How does the lotic ecosystem recover after the disappearance of a dammed lake, and what new ecological balances result?
• What effects will the removal works have on the quality of the environment and its consequences for the biocenoses that develop there?
• What are the ecotoxicological risks associated with accumulated silt for aquatic animal and plant communities?

Methods

The characterisation of the communities is carried out via in situ sampling of the communities in place. In addition, artificial substrates are installed at each station in order to standardise habitats and substrates from upstream to downstream and thus to facilitate inter-site comparisons.

At the same time, the identification of ecotoxicological risks is being monitored in particular at the confluence of the Yvrande by the in situ exposure of sentinel organisms (bryophytes, microalgae and invertebrates) and the study of the bioaccumulation of heavy metals (in particular cadmium) in the various biological compartments. Experiments on the risks of contamination linked to the dredging of the Yvrande are also being carried out during the dredging work.

Laboratories involved

• ECOBIO – UMR Ecosystems, Biodiversity, Evolution, CNRS/Université Rennes 1, Rennes
• ESE – UMR Ecology and Ecosystem Heath, INRA/Agrocampus Ouest, Rennes
• OSUR – UMS Rennes Observatory of the Sciences of the Universe, CNRS, Rennes