Vol. 4, Issue 2, Part D (2022)

The biology of Chadian freshwater aquatic environments is little known and works on benthic macroinvertebrates dates back to at least the 1980s thanks to the work of the office for scientific and technical research overseas (ORSTOM). This study was carried out in the Chari River, Bahr Kôh Department (Moyen Chari) over a distance of 52 km on the edge of the town of Sarh in order to assess the family diversity of macroinvertebrates.
Sampling was carried out in shallow environments with a weak current. A haze net constituted of a 1 m long sleeve and a collector with a circular opening of 30 cm diameter and a mesh size of 500 µm was used following the multi-habitat approach according to the Barbourt method adapted by Stark. Sampling was carried out on a monthly basis during the flood period from August to November 2020, which corresponds to the period of maximum lateral expansion of the Chari, and during the low-water period from February to May 2021, which corresponds to the period when the water level of the Chari reached its lowest point. The fauna surveyed is composed of 10464 individuals belonging to 98 families, 17 orders and 7 classes. Insects are the most represented and constitute 76.53% of the total richness of the macrofauna collected, followed by molluscs composed of 13.26%, including 9.18% of gastropods. Annelids, Crustacea and Chelicerata were the groups with the lowest number of individuals (of the population). Chironomidae and Dytiscidae had the highest total family richness, while Thiaridae was the most abundant family. The Kruskal-wallis test was applied to explain the good spatiotemporal diversity of the stands. Depending on the season, low diversity was observed at the end of low water and during high water. The high taxonomic richness of the entomofauna, dominated by pollutants, at stations where human activities are taking place indicates a state of disturbance linked to pollution.  While the spatial distribution of total abundance was dominated by Molluscs (Thiaridae, Corbiculidae) in the downstream stations is explained by the mineralisation and enrichment in organic matter of these stations.