No abstract

Lake Léré is situated in the Mayo-Kebbi locality southwest of Chad, it is the site for RAMSAR since 2001 hosting manatee (Trichechus senegalensis). This lake has been under study with the aimed of determining the structure of zooplankton community from February 2016 to April 2017. For this study, three sampling stations were chosen and divided into 2 to 3 layers from water surface towards the bottom. A total of 49 zooplanktonic species were identifiedin LakeLéré. This was dominated by Rotifers community with more than 75% (38 species).Rotifers and Copepodsdominated withabundance proportions of 78.10 and 60.04% respectively in the dry season. This was relatively higher compared to the rainy season (21.89 and 39.95%). In the Cladocère communities, a higherabundance was observed in the rainy season of 85.39% and 14.6% in the dry season. Therewere no significant differences between the physicochemical parameters, the sampling stations and between the different sampling levels.Thehigh values of Sorensen similarity index, shows the homogeneity of the waters of the lake and justifies the absence of significant differences in the specific richness between stations. The specific richness of zooplankton community in Lake Léré and its physico-chemical variables lead to a conclusion of the mesotrophic state of the lake's waters.

One of the major challenges of aquatic ecology is to understand how anthropization affects biodiversity and what the consequences on the functioning of hydrosystems. Physicochemical and zoolanktonic variables studied in two ponds (Mokolo and Mopa) in the city of Bertoua, with two sampling stations (surface and depth) per pond and data collected monthly from March 2016 to April 2017 (14 months) allowed us to appreciate the spatial and seasonal dynamics of zooplankton in relation to anthropogenic disturbances. Abiotic variables of the ponds show that they are highly anthropized with relatively high temperatures (> 23 °C), low water transparency (< 70 cm) despite the shallow depth of the ponds (< 170 cm), average oxygenation (> 50%) with hypoxia (< 35%) recorded in the rainy season, high mineralization of the waters, high levels of nutrients, organic matter and photosynthetic pigments (> 30 µg/L). These characteristics allow to classify these water bodies in the category of hypereutrophic ponds. Biological data show fairly diverse ponds with 63 species identified in Mokolo Pond representing 17.89% of the total abundance. In Mopa Pond, 75 species were identified representing 21.30% of the total abundance. This study allowed us to deduce that the structure and dynamics of microcrustaceans communities are under the control of different processes that interact simultaneously. It is mainly influenced by the season, predation and by the depth of sampling, the month and the station having no influence on this distribution.

In Cameroon, rivers are subjected to physicochemical disturbances, which increase the degradation of water quality. The aim of this study was to determine the spatio-temporal diversity of the phytoplankton groups and to evaluate the environmental parameters of the sampling sites in order to assess the quality of water in two hydrographic networks. Physicochemicals analyzes were carried out according to the standard methods while phytoplankton organisms were harvested by direct sampling and analyzed by the Utermöhl method. The analysis of Ammonia Nitrogen, Dissolved Oxygen, Electric Conductivity, Nitrates, Orthophosphates, pH, Temperature, and Turbidity.of water revealed the poor state of health of the water. Data from the Long Dry Season differed significantly (p < 0.05) from those recorded in other seasons. The phytoplankton communities were made up of Chlorophyta, Chrysophyta, Cyanophyta, and Euglenophyta with 11 classes dominated by Bacilliarophyceae (12 210 Ind/mL) and Cyanophyceae (6 208 Ind/mL). Phytoplankton densities were higher the Long Rainy Season and much lower in the Small Dry Season than in the Long Dry Season. Station near NODISCAM indicated significant organic pollution under the effect of agro-industrial discharges operating upstream of this company. For this station, the different values showed significant differences (p < 0.05) from one station to another. Finally, spatio-seasonal variations of phytoplankton densities showed logical responses to changes of physicochemical conditions in the environment. This work highlights the need to treat wastewater from collection channels before its dump into the natural environment, to prevent progressive eutrophication of the receiving aquatic environment, and poisoning by water consumption.