# Nutrient release from anoxic sediments in a dam reservoir: a mesocosm study

Clara Garyga, Jean-Christophe Clement, Javier Vidal-Hurtado, Antoine Exandier, Ilann Bourgeois

► To cite this version:

Clara Garyga, Jean-Christophe Clement, Javier Vidal-Hurtado, Antoine Exandier, Ilann Bourgeois. Nutrient release from anoxic sediments in a dam reservoir: a mesocosm study. SFE² 2024, International Congress in Ecology and Evolution, Oct 2024, Lyon, France. . [hal-04819653](https://hal.science/hal-04819653v1)

HAL Id: hal-04819653

https://hal.science/hal-04819653v1

Submitted on 13 Dec 2024

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# Nutrient release from anoxic sediments in a dam reservoir :
a mesocosm study

<figure><img src="image_1.png" /></figure>

Clara Garyga¹,², Jean-Christophe Clément², Javier Vidal Hurtado², Antoine Exandier² Ilann Bourgeois²

¹EDF R&D, LNHE, Chatou, France

²Univ. Savoie Mont Blanc, CARRTEL, Chambéry, France

Contact : clara.garyga@edf.fr

CARRTEL

<figure><img src="image_2.png" /></figure>

CENTRE ALPIN DE RECHERCHE
SUR LES RESEaux TROPIQUES
ET ECOsYsTEMES LINNIQUES

## Introduction

In this study a mesocosm experiment was set up to determine the influence of dissolved oxygen concentrations in the water column on nutrient fluxes at the sediment-water interface.

## Context

<figure><img src="image_3.png" /></figure>

* Dam reservoirs face **eutrophication-related issues** due to the accumulation of nutrients (N, P) partly from sediments.

* Dissolved oxygen (DO) concentration in the water column influence greatly nutrient dynamics at the sediment-water interface.

## Materials and methods (Gautreau et al., 2020)

### Sediment sampling and preparation

**Study site** : Hydroelectric reservoir of Eguzon (36)

<figure><img src="image_4.png" /></figure>

### Experimental system

**Peristaltic pump** :
to avoid dissolved oxygen gradients in the
column

<figure><img src="image_5.png" /></figure>

Air source

Water

Sediment

* The purpose of the experiment is to measure the influence of water column oxygenation (oxic and anoxic conditions) on nutrient fluxes at the water-sediment interface by regular water sampling.

* The experiment is carried out over 35 days, including a 20-day period of stabilization under oxic conditions and a 15-day period during which both treatments are in place and the water samples are collected.

## Impact of DO concentrations on the composition of the overlying water

<figure><img src="image_6.png" /></figure>

<figure><img src="image_7.png" /></figure>

* For both treatments, nitrate and phosphate concentrations remain below the detection limit (results not shown).

* In anoxic conditions, there is a significant release of organic nitrogen, phosphorus and carbon from the sediments, which could be explained by the resuspension of sediments in the column.

<figure><img src="image_8.png" /></figure>

Anoxic columns
at the end of the
experiment

Oxic columns at
the end of the
experiment

<figure><img src="image_9.png" /></figure>

* In anoxic conditions, total iron and manganese concentrations increase progressively throughout the experiment.

* This could indicate a reduction of iron and manganese oxides under anoxic conditions.

## Conclusion

* The sediment was probably resuspended in the water under anoxic conditions.

* The results suggest a reduction in iron and manganese oxides, but surprisingly no phosphate was released from the sediments in anoxic conditions.

**Cited reference** : Gautreau, E., L. Volatier, G. Nogaro, E. Gouze, P. Marmonier & F. Mermillod-Blondin, 2020. The influence of bioturbation and water column oxygenation on nutrient recycling in reservoir sediments. Hydrobiologia 847: 1027-1040. https://doi.org/10.1007/s10750-019-04166-0