Reduced phosphorus loads from the Loire and Vilaine Rivers were accompanied by increasing eutrophication in Vilaine Bay (South Brittany, France)

Type Article
Date 2019-04
Language English
Author(s) Ratmaya Widya1, Soudant DominiqueORCID2, Salmon-Monviola Jordy3, Plus MartinORCID5, Cochennec-Laureau NathalieORCID1, Goubert Evelyne4, Andrieux Francoise5, Barillé Laurent6, Souchu Philippe1
Affiliation(s) 1 : Ifremer , LER MPL, Rue de l'Ile d'Yeu, BP 21105, 44311 Nantes CEDEX 03, France
2 : Ifremer, VIGIES, Rue de l'Ile d'Yeu, BP 21105, 44311 Nantes CEDEX 03, France
3 : INRA/Agrocampus Ouest – UMR1069 Sol Agro et Hydrosystème Spatialisation, 35000 Rennes, France
4 : Université de Bretagne Sud – GMGL, UMR CNRS 6538 DO, Campus Tohannic, 56000 Vannes, France
5 : Ifremer, DYNECO PELAGOS, ZI Pointe du Diable, 29280 Plouzané, France
6 : Université de Nantes, Mer Molécules Santé EA 2160, Faculté des Sciences et des Techniques, BP 92208, 44322 Nantes CEDEX 3, France
Source Biogeosciences (1726-4170) (Copernicus GmbH), 2019-04 , Vol. 16 , N. 6 , P. 1361-1380
DOI 10.5194/bg-2018-406
WOS© Times Cited 2
Abstract

The evolution of eutrophication (i.e., phytoplankton biomass) during recent decades was examined in the coastal waters of Vilaine Bay (VB, France) in relation to those in their main external nutrient sources, the Loire and Vilaine Rivers. Dynamic Linear Models, corroborated by the Mann-Kendall test, were used to study long-term trends and seasonality of dissolved inorganic nutrient and chlorophyll a concentrations (Chl a) in rivers and coastal waters between 1980 and 2013. The reduction in dissolved riverine inorganic phosphorus concentrations (DIP) from the early 1990s led to the decrease in their Chl a levels. However, dissolved inorganic nitrogen concentrations (DIN) decreased only slightly in the Vilaine and actually increased in the Loire, especially during summer. Simultaneously, phytoplankton in the VB has undergone profound changes with: (1) increase in biomass, (2) change in the position of the annual peak from spring to summer, and (3) increase in diatom:dinoflagellate ratios, especially in summer. The increase in phytoplankton biomass in VB, particularly in summer, was probably due to increased DIN loads from the Loire, sustained by internal regeneration of DIP and dissolved silicate from sediments. This long-term ecosystem-scale analysis reports the consequence of nutrient management scenarios focused solely on P reduction. Freshwater ecosystems upstream reveal successful recoveries through the control of P alone, while eutrophication continues to increase downstream, especially during the period of N limitation. Therefore, nutrient management strategies, paying particular attention to diffuse N-sources, are required to control eutrophication in receiving coastal waters

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How to cite 

Ratmaya Widya, Soudant Dominique, Salmon-Monviola Jordy, Plus Martin, Cochennec-Laureau Nathalie, Goubert Evelyne, Andrieux Francoise, Barillé Laurent, Souchu Philippe (2019). Reduced phosphorus loads from the Loire and Vilaine Rivers were accompanied by increasing eutrophication in Vilaine Bay (South Brittany, France). Biogeosciences, 16(6), 1361-1380. Publisher's official version : https://doi.org/10.5194/bg-2018-406 , Open Access version : https://archimer.ifremer.fr/doc/00461/57244/