Interactions between aquatic and riparian zones

RESTAURE: Restoring ecosystems following the removal of dams: a functional approach to interactions between aquatic and riparian zones

Coordinator(s)

Christophe Piscart and Simon Dufour

Scientific context

Removing the dams on the Selune will change the way the river and its ecosystems function. Exchanges of nutrients, matter and energy from the terrestrial part of a river's catchment area to its aquatic part will be modified. In addition, the disappearance of the reservoirs will favor the recolonisation of the river and the newly emerged banks by aquatic and terrestrial fauna and flora.

Nowadays, the aquatic environment is no longer considered as a simple receptacle, but as an environment that interacts with the terrestrial environment. These interactions represent a blind spot in research into the ecological restoration of river systems. Analysing the interactions between the aquatic zone and the riparian zone on the Selune therefore represents a unique scientific opportunity to understand the ecological mechanisms that underpin not only resilience, but also the overall functioning of ecosystems.

Subject(s) of study

The project focuses on the interactions between riparian and aquatic ecosystems, and in particular between river morphology, riparian vegetation and aquatic and terrestrial invertebrates.

Objectives

This research project studies the neo-habitats resulting from the restoration of the Selune, focusing on terrestrial/aquatic interactions. The aim is to analyse how biological processes in aquatic and terrestrial ecosystems interact with the dynamics of river forms. This will enable us to understand the specific role of these interactions in the resilience of ecosystems undergoing restoration.

The sampling logic proposed for this project is based on the desire to analyse sites with contrasting environmental conditions. This will ultimately make it possible to determine their relative importance in the restoration process (surrounding land use with or without trees, more or less steeply sloping topography, etc.) and to compare these sites with sites located outside the reservoir zone.

Methods

Two axis are studied:

The interaction between riparian vegetation and channel morphology

These interactions are studied at three scales:

• At the scale of the former Vezins reservoir: comparison of aerial photographs acquired in 2019 and 2021 to understand the dynamics of bank erosion, surveys and mapping of vegetation cover to understand vegetation dynamics.
• At 4 study stations in the former reservoir with different characteristics (intensity of works, effect of emptying): topographical transects, vegetation surveys, drone images.
• At the river scale: by comparing the surveys carried out at the stations in the former Vezins reservoir with other stations located outside the area of influence of the dams.

Trophic interactions between riparian and aquatic ecosystems

Monitoring of aquatic and terrestrial invertebrate communities, biofilms in the water and more detailed floristic surveys are carried out at 6 study stations (3 control stations and 3 stations in the former reservoir). Food web analyses are carried out on the collected samples in order to understand the interactions between aquatic and terrestrial plant and animal communities.

Laboratories involved

• ECOBIO - UMR Ecosystems, Biodiversity, Evolution, Rennes
• LETG - UMR Coastline Environment Remote sensing Geomatics, Rennes et Caen
• DECOD - UMR Dynamics and sustainability of ecosystems: from source to ocean, INRAE/Institut Agro/Ifremer, Rennes