Assessment of the diversity, ecology, and spatiotemporal dynamics of the phytoplankton community in the Tono Dam, Ghana

Abstract

The present study sought to determine the phytoplankton diversity, distribution, and abundance in the Tono Dam in the Upper East Region of Ghana. Three (3) different geographical strata (SI, SII, and SIII) of the dam were demarcated for sampling across four (4) hydrological seasons (dry, pre-wet, wet, and post-wet seasons). From January to December 2020, phytoplankton samples were collected using a 53 µm mesh net, towed by a nonmotorized canoe at a speed of 0.60 ms⁻¹ against the dam’s water current. Physicochemical properties of the dam water were also assessed. A total of 25 phytoplankton species across five classes – Chlorophyceae, Cyanophyceae, Bacillariophyceae, Dinophyceae, and Chrysophyceae – were identified, with Chlorophyceae being the most diverse class (40%). Ulothrix sp. and Planktothrix sp. were consistently present in all strata of all seasons, while species like Tetraedron sp. and Volvox sp. had a more restricted presence. The highest Shannon-Weiner diversity index (H′) occurred during the wet season (1.72), and the lowest in the dry season (1.37). Species richness (SR) was high except in the pre-wet season (0.03). The evenness index (J′) was high in the wet season (0.65) and low in the dry season (0.49). Water temperature and nutrient levels varied significantly across seasons, with temperature being lowest in the wet season (26.5 ± 0.4 °C) and highest in the dry season (33.7 ± 0.3 °C). Ammonium levels peaked during the wet season (0.066 ± 0.03 mg/L). Redundancy analysis revealed correlations between phytoplankton species and physicochemical parameters. For instance, ammonium levels were positively correlated with Oscillatoria sp., dissolved oxygen (DO) with Synedra sp., and conductivity with Microcystis sp. Overall, the study confirmed the Tono Dam maintains healthy productivity levels. Effective management necessitates monitoring nutrient levels, adapting to seasonal and spatial variations, promoting sustainable agriculture, and implementing conservation strategies. These measures are essential to sustaining water quality, biodiversity, and fisheries productivity while addressing climate change impacts.