Phytoplankton Community Structure, Cyanobacterial Proliferation, and Water Quality Relationships in the River Benue Basin, Adamawa State, Nigeria
DOI:
https://doi.org/10.33003/Keywords:
Phytoplankton, Bacillariophyta, Cyanobacteria, Fragilaria, Anabaena, Shannon Diversity, River Benue, Freshwater Ecology, NigeriaAbstract
Phytoplankton communities are sensitive bioindicators of freshwater ecosystem health, yet their composition, diversity, and cyanobacterial status have never been quantitatively characterised for the River Benue Basin, Adamawa State, Nigeria. This study presents the first multi-location quantitative assessment of phytoplankton composition, abundance, and diversity across three contrasting anthropogenic pressure zones, and evaluates the public health significance of toxigenic cyanobacterial genera. Phytoplankton were collected monthly at Boronji, Dasin Hausa, and Njoboliyo during dry (February–April 2025) and rainy (June–August 2025) seasons by horizontal net towing (55 µm mesh), preserved in Lugol's iodine, and enumerated using Sedgewick-Rafter chambers under compound microscopy. Diversity was assessed using Shannon-Wiener (H') and Pielou's evenness (J') indices. Nineteen taxa were recorded at Boronji and Njoboliyo, and 20 at Dasin Hausa, spanning four divisions: Bacillariophyta, Chlorophyta, Cyanobacteria, and Chrysophyta. Fragilaria sp. dominated at all sites, peaking at 17,783 ind./L at Dasin Hausa, which also recorded the highest total abundance (46,895 ind./L), followed by Njoboliyo (27,636 ind./L) and Boronji (26,713 ind./L). Shannon-Wiener indices ranged from H' = 1.94 (Njoboliyo) to H' = 2.27 (Boronji). Four toxigenic genera Anabaena, Aphanocapsa, Oscillatoria, and Aphanizomenon occurred at all locations throughout the study, with Oscillatoria anomalously elevated at the most metal-contaminated site, Njoboliyo (868 vs. 282–284 ind./L elsewhere). The basin has crossed ecological thresholds enabling sustained cyanobacterial establishment at all sites; the Chlorophyta/Bacillariophyta ratio is identified as a sensitive bioindicator of heavy metal stress. Cyanobacterial surveillance and riparian buffer restoration are recommended as priority actions.
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Copyright (c) 2026 Aminu Maulud Abdulazeez, Tizhe Kwaga, Callistus Akosim, Nuru Zakari
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