Dramatic changes in a phytoplankton community in response to local and global pressures: a 24-year survey of the river Loire (France)

• Published in: Global Change Biology
• Main Authors: Larroudé, S., Massei, Nicolas, Reyes-Marchant, P., Delattre, C., Humbert, J.F.
• Other Authors: Biogéochimie et écologie des milieux continentaux (Bioemco), École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut de Recherche pour le Développement (IRD)-Institut National de la Recherche Agronomique (INRA)-Université Pierre et Marie Curie - Paris 6 (UPMC)-AgroParisTech-Centre National de la Recherche Scientifique (CNRS), Morphodynamique Continentale et Côtière (M2C), Université de Caen Normandie (UNICAEN), Normandie Université (NU)-Normandie Université (NU)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Rouen Normandie (UNIROUEN), Normandie Université (NU)-Centre National de la Recherche Scientifique (CNRS), Asconit Consultants, EDF R&D (EDF R&D), EDF (EDF), Electricite de France (EDF)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2013
• Subjects: cyanobacteria; herbicides; large river; NAO; phosphorus decrease; phytoplankton community; NORTH-ATLANTIC OSCILLATION; FRESH-WATER CYANOBACTERIA; LARGE EUTROPHIC RIVER; BLUE-GREEN-ALGAE; CLIMATE-CHANGE; HARMFUL CYANOBACTERIA; TOXIC CYANOBACTERIUM; LAKE PHYTOPLANKTON; MIDDLE LOIRE; MICROCYSTIS-AERUGINOSA; [SDE.BE]Environmental Sciences/Biodiversity and Ecology; North Atlantic; North Atlantic oscillation
• Online Access: https://hal-bioemco.ccsd.cnrs.fr/bioemco-00840233; https://doi.org/10.1111/gcb.12139

International audience The impact of climate change and of other anthropogenic pressures on the structure and composition of phytoplankton communities of large European rivers remains poorly documented. Here we report the findings of a study of the changes in the phytoplankton community of the middle segment of the river Loire over the past 24 years. An attempt is made to distinguish between the impact of changes acting at the local scale and that of those acting more globally. A dramatic reduction in phytoplankton abundance was observed, particularly in the mid -1990s; this was concomitant with an increase in the relative proportion of cyanobacteria. At the same time, the phytoplankton community displayed increasing richness and diversity, and little change in its size structure. All these changes seem to be related to local changes, in particular to the reduction in phosphorus concentrations, as well as to changes in climate, throughout modifications in the river discharge and water temperature. Interestingly, herbicide contamination also appeared to be of particular importance in explaining the unexpected increase in the proportion of cyanobacteria in the phytoplankton community after the 1990s. These findings suggest that combinations of numerous anthropogenic pressures acting at different spatial and temporal scales have led to a mix of predictable and unpredictable changes occurring in the phytoplankton community of the river Loire, with probable consequences for the trophic networks in this river.