Titre de l’article: Anthropogenic impacts on water quality and macroinvertebrates distribution of Toho Lake, South-West Benin

Abstract

The impact of the anthropogenic activities on the distribution of the macrobenthic organisms of Toho Lake was conducted. Ten physico-chemical parameters were measured and benthic organisms were collected from May to August 2016 at 8 stations with an Eckman grab. The auto-organizing map SOM was used to determine the similarity between stations according to the environmental variables. (species richness, relative abundance, Shannon-Weiner and Pielou’ equitabiliy indices). Abundance-biomass Comparison (ABC) indices, Difference in Area by Percent (DAP) and Shannon-Wiener Equitability Proportion (SEP) were used to reveal ecological stress in the lake In total, 23 species of macroinvertebrates gathering into18226 individuals divided into 4 classes (Insects, Gastropoda, Achaeta and Arachnids) were inventoried. The insects (20 species representing 91% of the specific richness and 99. 01% of the total individuals) had largely dominated this fauna with one species, Enithares sp.. Few water parameters (water transparency (40 - 90 cm), water temperature (26.50 - 30.3 °C), conductivity (213 - 350 mS/cm) and dissolved oxygen (1.75 - 6.06 mg/L)) varied significantly in time whereas depth (0.60 - 1.68 m)showed spatial variation. Three clusters, discriminated by SOM analysis revealed stresses on the organisms. The feeble values of Shannon and equitability indexes and the stress’ index calculated have largely supported the impacts of anthropogenic activities on the distribution of species dominated by few taxa showed to be indicators of the ecological status of this ecosystem.