Composition and seasonal distribution of diatom in human-influenced rivers in tropical Africa: Nonnhon and Gninhin rivers (West Africa)

Résumé

The study was conducted to describe the temporal and spatial distribution of diatoms communities of the rivers Nonhon and Gninhin that are impacted by agricultural and mining activities respectively. Sampling was carried out every 45 days from October 2020 to February 2022 at three stations on each rivers following two climatic seasons. 31 taxa, 12 genera, 12 families, 5 orders and 2 classes were identified. Abundance varies between 18 x 10⁵ Cell/L and 40 x 10⁵ Cell/L and between 30 x 10⁵ and 126 x 10⁵ Cell/L respectively in Nonhon and Gninhin Rivers. In Nonhon River, extreme values of Shannon diversity index (1.42 and 2.14) were noted during dry season at stations NO1 and NO3 respectively. Maximum (0.90) and minimum (0.71) values of evenness index were recorded during rainy season at stations NO2 and NO3 respectively. Concerning Gninhin River, Shannon diversity index values fluctuated between 0.73 and 2 respectively at stations GN1 and GN2 during rainy season. Evenness values oscillated between 0.32 and 0.82 respectively at GN1 and GN2 during dry season. The lack of homogeneity of the appearance of taxa indicates dominance of a few taxa with high abundance, which is an indicator of the existence of environmental pressure. We absolutely must raise awareness among the local population about ecological standards for the conservation of the ecological integrity of the two rivers.