Seasonal dynamics of plankton populations and phytoplankton photosynthetic activity in a highland fish pond in tropical West Africa
Compared to the East/Central regions of Africa, little research efforts have focused on West African tropical limnology. This study, conducted on a freshwater ecosystem, Panyam fish pond, in the highland region (Plateau State) of tropical West Africa, provides knowledge on the hydrochemical characteristics and seasonal or annual biomass oscillations corresponding to the distinguishable climatic phases characteristic of the region. Physiographic phenomenon ‘Harmattan’ (North-East Trade Winds) induced low temperature conditions (<11°C) during December to January. Moderately dilute waters are reflected by relatively low ionic content (average conductivity of 77 μS cm−1), conforming to the category II of African waters, based on the classification of Beadle (1981). Seasonal algal succession was marked by its abundance relative to the beginning of the rainy season (May to September). The sequence of annual phytoplankton dominance was Chlorophyceae>Cyanophyceae>Bacillariophyceae. The dominance for zooplankton was Rotifera>Crustaceae. The occurrence of fewer Cladocera and Copepoda in the Panyam pond is an observation consistent with the findings for other tropical water systems. These results further support the contention that seasonal or annual biomass oscillations in the tropics are not systematically lower than in the temperate zone. The observed phytoplankton productivity rates (average value of 4.86 g C m−2 day−1) are higher than those reported by Talling (1965) for African waters. A considerable proportion of the net production (64.3%) was comprised of gross production (1760 g C m−2 day−1). The observed relatively enhanced respiratory values (25.4–41.5%) are characteristic of tropical waters. Further, more robust studies will work to remedy the paucity of knowledge regarding tropical West African limnology.