Browsing by Author "Sous la direction de : Professeur Claver Sibomana"

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    Impacts de la jacinthe d’eau eichhornia crassipes sur les paramètres physico-chimiques et la diversité piscicole dans le littoral NORD-EST DU LAC TANGANYIKA
    (UB, FS, 2025-04) NIGARURA, Ariel; Sous la direction de : Professeur Claver Sibomana
    Lake Tanganyika is an ancient ecosystem with very high biodiversity and great importance for the populations and bordering countries. The greatest biodiversity is found in the littoral zone. However, this lake is subject to threats that can lead to the loss of its biodiversity, including fish, and the degradation of water quality. The presence of water hyacinth, an invasive plant, in the littoral zone, constitutes a threat because it can reduce primary production and oxygen levels by reducing the brightness in the water. This invasive plant is highly present in the littoral zone of Bujumbura Bay, around the mouths of the Ntahangwa and Kinyankonge rivers, making this part of the lake vulnerable. Therefore, this study was undertaken to determine the impact of the water hyacinth invasion on fish diversity and water quality in this area. Four sampling sites were selected at the mouths of the Kinyankonge and Ntahangwa rivers based on the presence or absence of water hyacinth. Collection lasted 4 months and covered two seasons. Shannon diversity, Piélou evenness, and Jaccard similarity indices were measured to estimate fish biodiversity. Fish data were collected by gillnet fishing and survey while physicochemical parameters were measured in situ and by laboratory analysis. A total of 53 species divided into 9 families were identified, of which the Cichlid family with 44 species (85% of the total species) was predominant. The values of the diversity indices show that biodiversity is high at sites with water hyacinth. Furthermore, the Jaccard index indicates a great similarity between the sites invaded by water hyacinth at the mouths of the two rivers. The results of the survey show that some species that were fished before the colonization by water hyacinth are no longer present in the fishermen's catches, including Mastacembellus cunningtoni and Astatotilapia burtonii while others that were previously absent are currently fished like Clarias gariepinus, Protopterus aethiopicus and Simochromis diagramma. The results on physicochemical parameters show that pH, electrical conductivity, TDS and phosphates are higher at sites colonized by hyacinth during the dry season. However, the values of nitrites, oxygen concentration, dissolved oxygen, ammonium and BOD5 do not vary according to the presence of water hyacinth or seasonal variation. The presence of water hyacinth in the lake Tanganyika would have led to the disappearance of some fish species and the establishment of others. It also has an influence on the quality of physicochemical parameters. The results of this study should help policymakers and institutions responsible for environmental protection to take the necessary measures to control the proliferation of water hyacinth to limit the disruption of Lake Tanganyika.