Phytoplanktonic diversity of some rice-growing dams in yamoussoukro (Côte d’Ivoire)

Many small dams for agropastoral purposes have been initiated in various regions of the country, with the aim of promoting economic and social development, particularly to facilitate rice yields. These aquatic environments are home to an important biodiversity, including phytoplankton, which are not well known and likely to be impacted by human activities. The objective of this work is to know the phytoplankton population of the Yamoussoukro rice-growing dams in order to prevent the risks of eutrophication. The physico-chemical parameters of the water were measured with a multi-parameter HANNA model HI 98194 in three stations (Nanan, Subiakro and Zatta). Nutrient salts were measured using HANNA digital mini-photometers model H1781. Taxa were sampled with a plankton net of 20 µm mesh size. A photonic microscope was used to observe the different samples collected. In total, one hundred and fourteen (114) phytoplankton taxa were inventoried and divided into for (4) phyla: Chlorophyta (44 taxa or 39%), the Euglenophyta (41 taxa or 36%), Cyanoprokaryota (16 taxa or 14%) and Heterokontophyta (13 taxa or 11%). Water reservoirs could be considered rich in taxa. Chlorophyta and Euglenophyta contain the greatest diversity and constitute more than half of all taxa collected. The study also revealed that the reservoirs are warm (29.86°C) and acidic with low dissolved oxygen (2.25 mg/l) and high nutrient values (ammonium, nitrate, nitrite and ortho-phosphate). This mineralization of these waters explains the high diversity of taxa in the Yamoussoukro dams.