Phytoplankton diversity and trophic state of natural water reservoirs in Azagny National Park (Côte d'Ivoire)

Abstract

Azagny National Park, located 40 kilometres from the town of Grand-Lahou, is home to numerous animal and plant species, including microalgae. The aim of this study was to determine the phytoplankton diversity and trophic status of the water reservoirs in the Azagny National Park. The physico-chemical parameters of the water were measured at stations ST1, ST2 and ST4, from March 2019 to February 2020. Nutrient salts were measured using a spectrophotometer. Phytoplankton sampling was carried out using a plankton net with a mesh size of 20 µm. A total of 134 phytoplankton taxa were inventoried, divided into 5 phyla, 8 classes, 14 orders and 32 families. The waters of the Azagny National Park could be considered rich in taxa, with the majority being Heterokontophyta (48 taxa) and Euglenophyta (39 taxa), followed by Chlorophyta (27 taxa), Cyanoprokaryota (18 taxa) and Dinophyta (2 taxa). Sorensen's index or coefficient of similarity gave values ranging from 0.89 to 0.74, showing that the Park's water reservoirs have taxa distributed in the same way in the different stations. The study also revealed that the park's reservoirs are warm and acidic, with low levels of dissolved oxygen and high levels of nutrient salts (nitrite and phosphate). The A and B index values of 9.81 and 1.62 respectively show that the park's reservoirs are tending towards a state of eutrophy.