Assessment of some key indicators of the ecological status of an African freshwater lagoon (Lagoon Aghien, Ivory Coast)

Type Article
Date 2021-05
Language English
Author(s) Koffi Ahoutou Mathias1, 2, Yao Djeha Rosine1, Kouamé Yao Eric1, Quiblier Catherine3, 4, Niamen-Ebrottié Julie5, Hamlaoui Sahima3, Tambosco Kevin6, Perrin Jean-Louis7, Troussellier Marc8, Bernard Cecile3, Seguis Luc7, Bouvy Marc8, Pédron Jacques6, Koffi Konan Felix2, Humbert Jean-FrançoisORCID6, Kalpy Coulibaly Julien1
Affiliation(s) 1 : Institut Pasteur d’Abidjan, Abidjan, Cote d’Ivoire
2 : Universite´ Jean Lorougnon Guede , Daloa, Cote d’Ivoire
3 : MNHN, UMR 7245 Molecules de Communication et Adaptation des Micro-organismes, Paris, France
4 : Universite de Paris, Paris, France
5 : Laboratory of Environment and Aquatic Biology, Nangui Abrogoua University, Abidjan, Cote d’Ivoire
6 : iEES Paris, INRAE-Sorbonne Universite , Paris, France
7 : HydroSciences Montpellier, IRD, Universite de Montpellier, CNRS, Montpellier, France
8 : MARBEC, IRD-Universite de Montpellier, Montpellier, France
Source Plos One (1932-6203) (Public Library of Science (PLoS)), 2021-05 , Vol. 16 , N. 5 , P. e0251065 (18p.)
DOI 10.1371/journal.pone.0251065
Abstract

The supply of drinking water is a vital challenge for the people who live on the African continent, as this continent is experiencing strong demographic growth and therefore increasing water demands. To meet these needs, surface water resources are becoming increasingly mobilized because underground resources are not always available or have already been overexploited. This situation is the case in the region of Abidjan in the Ivory Coast, where the drinking water deficit is a growing problem and it is therefore necessary to mobilize new water resources to ensure the supply of drinking water. Among the potential resources, local managers have identified a freshwater lagoon, Lagoon Aghien, That is in close proximity to the city of Abidjan. With the aim of enhancing knowledge on the ecological functioning of the lagoon and contributing to the assessment of its ability to provide drinking water, several physical and chemical parameters of the water and the phytoplankton community of the lagoon were monitored for 17 months (December 2016-April 2018) at six sampling stations. Our findings show that the lagoon is eutrophic, as evidenced by the high concentrations of total phosphorus (>140 μg L-1), nitrogen (1.36 mg L-1) and average chlorophyll-a (26 to 167 μg L-1) concentrations. The phytoplankton community in the lagoon is dominated by genera typical of eutrophic environments including mixotrophic genera such as Peridinium and by cyanobacteria such as Cylindrospermopsis/Raphidiopsis, Microcystis and Dolichospermum that can potentially produce cyanotoxins. The two rainfall peaks that occur in June and October appeared to be major events in terms of nutrient flows entering the lagoon, and the dynamics of these flows are complex. Significant differences were also found in the nutrient concentrations and to a lesser extent in the phytoplankton communities among the different stations, especially during the rainfall peaks. Overall, these results reveal that the quality of the lagoon’s water is already severely degraded, and this degradation could increase in future years due to increasing urbanization in the watershed. These results therefore raise questions about the potential use of the lagoon as a source of drinking water if measures are not taken very quickly to protect this lagoon from increasing eutrophication and other pollution sources.

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Publisher's official version 18 2 MB Open access
S1 Fig. Variations in TN concentrations (A) at the six sampling stations, including station 3 (dashed rectangle), which was located close to the shore, and (B) at... 184 KB Open access
S2 Fig. Vertical profiles of water temperatures and dissolved oxygen concentrations at the six sampling stations from January 2017 to April 2018. 15 MB Open access
S3 Fig. Boxplot of the temporal variations in the genus richness and diversity (Shannon index) of the phytoplankton community in Lagoon Aghien. 68 KB Open access
S4 Fig. Principal component analysis was performed on the physical and chemical data and Chl-a concentrations collected at the six sampling sites from January 2017 to April 2018 (projection of ... 351 KB Open access
S1 Table. GPS coordinates and depth of the six sampling stations in Lagoon Aghien. 12 KB Open access
S2 Table. Data used to correct the underestimation of the Chl-a values provided by the YSI probe during the monitoring of Lagoon Aghien. 17 KB Open access
S3 Table. Temperature, turbidity and dissolved oxygen values recorded with the YSI probe at each sampling date and station during the survey. 13 KB Open access
S4 Table. Nutrient concentrations estimated at each sampling date and station during the survey. 14 KB Open access
S5 Table. Biovolume data of each genus estimated at each sampling date and station during the survey. 52 KB Open access
S6 Table. Distribution of the phytoplankton genera observed during the course of the study in Lagoon Aghien 22 KB Open access
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Koffi Ahoutou Mathias, Yao Djeha Rosine, Kouamé Yao Eric, Quiblier Catherine, Niamen-Ebrottié Julie, Hamlaoui Sahima, Tambosco Kevin, Perrin Jean-Louis, Troussellier Marc, Bernard Cecile, Seguis Luc, Bouvy Marc, Pédron Jacques, Koffi Konan Felix, Humbert Jean-François, Kalpy Coulibaly Julien (2021). Assessment of some key indicators of the ecological status of an African freshwater lagoon (Lagoon Aghien, Ivory Coast). Plos One, 16(5), e0251065 (18p.). Publisher's official version : https://doi.org/10.1371/journal.pone.0251065 , Open Access version : https://archimer.ifremer.fr/doc/00694/80584/