Nutrient transport and transformation in macrotidal estuaries of the French Atlantic coast: a modelling approach using C-GEM

Type Article
Acceptance Date 2021-01 IN PRESS
Language English
Author(s) Wei Xi, Garnier Josette1, Thieu Vincent1, Passy Paul2, Le Gendre Romain3, Billen Gilles1, Akopian Maia4, Laruelle Goulven GildasORCID5
Affiliation(s) 1 : UMR Metis 7619, Sorbonne Université, CNRS EPHE, 4 Place Jussieu, Paris, 75005, France
2 : UMR 8586 PRODIG, Université de Paris, 8 rue Albert Einstein, 75013 Paris, France
3 : Ecosystèmes et Aquaculture Durable, Unité de Recherche Lagons, IFREMER, Noumea, 98897, New-Caledonia
4 : Department of Research and Scientific Support, French Biodiversity Agency (OFB), 5 square Félix Nadar, 94300 Vincennes, France
5 : Department of Geosciences, Environment and Society, Université Libre de Bruxelles, Brussels, 1050, Belgium
Source Biogeosciences (1726-4189) (Copernicus GmbH) In Press
DOI 10.5194/bg-2021-164
Abstract

Estuaries are key reactive ecosystems along the land–ocean aquatic continuum, with significant ecological and economic value. However, they have been facing strong morphological management changes as well as increased nutrient and contaminant inputs, possibly leading to ecological problems such as coastal eutrophication. Therefore, it is necessary to quantify the ingoing and outgoing fluxes of the estuaries, their retention capacity, and estuarine eutrophication potential. A 1-D Carbon–Generic Estuary Model (C-GEM) was used to simulate the transient hydrodynamics, transport, and biogeochemistry for estuaries with different sizes and morphologies along the French Atlantic coast during the period 2014–2016 using readily available geometric, hydraulic, and biogeochemical data. These simulations allowed us to evaluate the budgets of the main nutrients (phosphorus [P], nitrogen [N], silica [Si]) and total organic carbon (TOC), and their imbalance with respect to estuarine eutrophication potential. Cumulated average annual fluxes to the Atlantic coast from the seven estuaries studied were 9.6 kt P yr−1, 259 kt N yr−1, 304 kt Si yr−1, and 145 kt C yr−1. Retention rates varied depending on the estuarine residence times, ranging from 0–27 %, 0–34 %, 2–39 %, and 8–96 % for TP, TN, DSi, and TOC, respectively. Large-scale estuaries had higher retention rates than medium and small estuaries, which we interpreted in terms of estuarine residence times. As shown by the indicator of eutrophication potential (ICEP), there might be a risk of coastal eutrophication, i.e., the development of nonsiliceous algae that is potentially harmful to the systems studied due to the excess TN over DSi.

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Wei Xi, Garnier Josette, Thieu Vincent, Passy Paul, Le Gendre Romain, Billen Gilles, Akopian Maia, Laruelle Goulven Gildas Nutrient transport and transformation in macrotidal estuaries of the French Atlantic coast: a modelling approach using C-GEM. Biogeosciences IN PRESS. Publisher's official version : https://doi.org/10.5194/bg-2021-164 , Open Access version : https://archimer.ifremer.fr/doc/00705/81713/