Impact of an exceptional winter flood on benthic oxygen and nutrient fluxes in a temperate macrotidal estuary: Potential consequences on summer deoxygenation

Type Article
Date 2023-02
Language English
Author(s) Hulot Vivien1, Metzger Edouard1, Thibault De Chanvalon Aubin2, Mouret Aurelia1, Schmidt Sabine3, Deflandre Bruno3, Rigaud Sylvain4, Beneteau Eric1, Savoye Nicolas3, Souchu Philippe5, Le Merrer YoannORCID5, Maillet Grégoire M.1
Affiliation(s) 1 : UMR 6112 LPG, Université d’Angers, Université de Nantes, Université du Mans, CNRS, Angers, France
2 : Université de Pau et des Pays de l’Adour, E2S UPPA, CNRS, IPREM, Pau, France
3 : Université de Bordeaux, CNRS, Bordeaux INP, UMR5805 EPOC, Pessac, France
4 : Univ. Nîmes, UPR 7352 CHROME, Nîmes, France
5 : IFREMER – LER, MPL, Nantes, France
Source Frontiers In Marine Science (2296-7745) (Frontiers Media SA), 2023-02 , Vol. 10 , P. 1083377. (16p.)
DOI 10.3389/fmars.2023.1083377
Keyword(s) estuary, water sediment exchanges, hypoxia, oxides-phosphorus interactions, flood

Despite 20 years of control on eutrophication, episodes of summer hypoxia still occur in the Loire estuary, impacting water quality and posing a key scientific and management challenge. This work aimed to quantify the contribution of the benthic compartment to hypoxia in the Loire estuary by direct measurement of water–sediment fluxes and an in-depth understanding of the seasonal variations of oxides and phosphorus stocks. During the summer’s low-discharge period, results show that the iron oxide-rich deposit is stable under hypoxic conditions, limiting the release of dissolved phosphorus into the overlying water column. The high nitrate content of the water column appears to be an important oxidizer of iron during hypoxic periods, limiting dissolved phosphorus leakage and aggravation of hypoxia. During the exceptional winter flood, significant sediment erosion associated with bubbling phenomena (attributed to methane efflux) created severe fractures in the sediment and stimulated water–sediment exchange. During the following months, these fractures were progressively filled, which decreased the intensity of benthic fluxes. However, due to the high residence time in the water during the summer period, a simple model demonstrated that benthic contributions were sufficient to directly (by direct oxygen consumption) or indirectly (by promoting ammonia oxidation) affect the oxygen stock in the water column during the low-discharge period. Our study demonstrates the importance of the benthic compartment in the occurrence of hypoxia and the obvious lack of knowledge to illustrate and model the biogeochemical functioning of the estuary.

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Hulot Vivien, Metzger Edouard, Thibault De Chanvalon Aubin, Mouret Aurelia, Schmidt Sabine, Deflandre Bruno, Rigaud Sylvain, Beneteau Eric, Savoye Nicolas, Souchu Philippe, Le Merrer Yoann, Maillet Grégoire M. (2023). Impact of an exceptional winter flood on benthic oxygen and nutrient fluxes in a temperate macrotidal estuary: Potential consequences on summer deoxygenation. Frontiers In Marine Science, 10, 1083377. (16p.). Publisher's official version : , Open Access version :