DOI: https://doi.org/10.36347/sajb.2025.v13i01.016

Pages: 159-163

Aboisso region is known for its high agricultural productivity, its numerous agro-industrial units and its gold panning activities. These sectors of activity could have consequences on water quality, and lead to changes in the composition and structure of micro-algae. This study aims to determine the trophic quality of some rivers in Aboisso region. Campaigns were conducted in four rivers N'Gotopkré, Anvo, Mouyassué and Toudoum. Phytoplankton samples were collected by horizontal traction over 6 m from surface water, using a plankton net with a 20 µm mesh size. The samples were observed using an Olympus CKX 41 optical microscope. Some books were used to identify phytoplankton species. The counting of phytoplankton was carried out using the Malassez cell and the counting unit was the cell. According determination of waters quality, Palmer method was used. A pollution index factor of 1 to 5 was assigned to 20 types of algae most tolerant to organic pollution. The microalgal flora recorded in the rivers consists of 31 taxa and divided into 3 phyla, Chlorophyta, Bacillariophyta and Cyanoprokaryota respectively with 15, 10 and 6 taxa. According to floral diversity, N’Gotopkré and Mouyassué rivers recorded the most taxa respectively with 18 and16 taxa. Analysis of phytoplankton densities indicated a predominance of Chlorophyta with 13.180.103 Cells/L and Mouyassué river with 13.080.103 Cells/L recorded the highest densities. The lowest floristic density was observed in Toudoum river with 740.103 Cells/L. According to the quality of rivers, among the 20 genera presented by Palmer (1969) as bio-indicators of organic pollution, 5 were identified in the rivers. These are the genera Oscillatoria, Scenedesmus, Navicula, Closterium and Pandorina. The different scores ranging from 0 to 13, showed values below organic pollution.