Mise à jour le 13 January 2022

Loire estuary function

Acquisition of knowledge

Background

Today, the Loire estuary is considered to be in a poor state with regard to the Water Framework Directive (WFD) Large Fish Indicator (LFI). In effect, some migratory species cannot manage to swim back up the Loire. One hypothesis is that it is due to recurrent periods of anoxia in the estuary’s silt plug. The cause cannot be mainly attributed to climate change as the other large estuaries are not impacted in the same way. As there is no clear reason for the particular situation in the Loire estuary, a diagnosis of the precise origin is necessary. The hypothesis put forward is that the estuary sediment stores reactive nutritive salts likely to be released in the water column where hypoxia occurs and/or is aggravated.

Schedule & Location

2nd quarter 2021 / 2nd quarter 2025

The action will be conducted on the entire Loire estuary, from its river part to the open marine environment, over a distance of almost 120 km.

Objective

The objective of this action is to draw up operational recommendations for identifying driving forces and for implementing actions for reducing or making up for episodes of anoxia, and to enable improved circulation of species.

Description of the action

This action is broken down into several sections :

1- Characterisation of phosphorus stocks and of the reactivity of sediments in the different estuary compartments

This work will be conducted on the basis of sampling in the field (oceanographic campaigns) and laboratory studies.

2- Quantification of phosphorus stocks and kinetics of mobilisation of inherited phosphorus by spatial and temporal modelling This task will be conducted based on the sampling work undertaken in point 1. Times series will also be determined.Satellite and airborne images will also be studied

3- Governance and recommendations for reducing the impact of phosphorus on the generation of hypoxia episodes

This work aims to present the results along and to provide material for the strategic directions taken for water bodies.

Main results expected

Estuary institutional stakeholder awareness (information letters)

Participation in a congress to present the results of the study

Publication of 2 scientific articles

Organisation of an event for estuary institutional and non-institutional stakeholders

List of recommendations to limit or make up for hypoxia in the Loire estuary (strategic diagnostic report)

All knowledge acquisition actions
All the actions