Harmful cyanobacterial efflorescence is of growing global concern and its prediction and management require a better understanding of the growth control factors and dominance of cyanobacteria. The Zit-Emba reservoir located in the NorthEast of Algeria, was constructed to provide drinking water, irrigation, and fishing. The vertical and seasonal distribution variation of cyanobacteria community associated with environmental factors was comprehensively investigated from April 2016 to December 2016 at five depths, based on a seasonal sampling. The cyanobacteria communities of this reservoir are composed of seven genera belonging to five orders. The average proportion of Microcystis to total cyanobacteria population was 43%, followed by Woronichinia 21%, Planktothrix 16%, Dolichospermum 13%, Oscillatoria 5%, and the remainder (Merismopedia, Spirulina) 2%. The average cyanobacterial abundance was 2702 cells/mL, ranging from 360 to 65 795 cells/mL and this abundance exceeds the alert level 1 throughout the year. The most recurrent periods of increase took place from spring to summer and autumn. However, the vertical distributions of cyanobacteria displayed a similar profile each season, and abundances tended to decrease with depth. The results of the statistical analysis suggested that the most abundant of cyanobacterial genera were positively related to chlorophyll-a and water temperature and negatively with the concentrations of NO 3-N, NH 4-N, and NO 2-N. This demonstration of toxigenic cyanobacteria in this drinking water production dam involves regular monitoring of the cyanobacterial communities and cyanotoxins in raw water.

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This study aims to inventory Cladocerans communities and determine their seasonal distribution according to certain environmental parameters in a natural shallow freshwater lake (Lake Oubeira) that El Kala National Park shelters. The values of chlorophyll-a and transparency observed during the study period indicate that the water body fluctuated between eutrophic and hypereutrophic status.Occurrence frequency of the 17 listed species revealed the dominance of Bosmina longirostris and the constancy of Ceriodaphnia lacustris. Among the 15 remaining species, 9 are regular (Oxyurella tenuicaudis, Alona guttata, Alonella exigua, Pleuroxus aduncus, Eubosmina coregoni, Ceriodaphnia rotunda, Moina brachiata, Diaphanosoma brachyurum, Diaphanosoma lacustris), 4 are incidental (Scapholeberis mucronata, Acroperus elongatus, Simocephalus serrulatus, Moina micrura) and 2 are rare (Macrothrix rosea, Sida crystallina). The number of species encountered in Oubeira waters is around 7, 17, 16 and 14 in spring, summer, autumn and winter respectively. In terms of abundance, the 7 species collected in the spring account for more than 88% of the total number of individuals collected. B. longirostris represents 9/10 of the overall density recorded by the Cladocerans collected. This species is highly abundant in spring (94% of its overall density) and correlated positively with transparency. C. lacustris, D. brachyurum, M. micrura, M. brachiata are absent in spring and are mainly present in summer and autumn; these species show positive correlations with water temperature, chlorophyll-a, nutrients and negative with transparency. It is also interesting to study the temporal dynamics of the various zooplanktonic groups and their interaction with phytoplankton and the fish inhabiting water bodies. Such studies need to be continued because they allow the creation of databases that will be used in biomonitoring programs and management of continental waters. Sehili et al., 2020 group of Palaeozoic origin, mainly composed of microzooplankton (Dodson and Frey, 2001; Forro et al., 2008). Also, Cladocerans (Crustacea: Branchiopoda), commonly known as water fleas, constitute an important element in freshwater lakes; According to Hessen et al. (2003), Mola and Ahmed (2015), these species largely contribute in zooplankton biomass and play a crucial role in trophic networks of freshwaters. As previously reported, Cladocerans were proved to be as important grazers of algae and detritus (Balayla and Moss, 2004), importantly involved in nutrient recycling in aquatic ecosystems (Hudson et al., 1999; Urabe et al., 2002) and considered as water quality indicators (Pinto-Coelho et al., 2005). The Cladoceran group feeds on bacterioplankton and very small algae (Nogueira, 2001) and affects the growth of bacterial population, heterotrophic protozoa, microalgae and even some rotifer species via trophic relationships and competition (Arnold, 1971; Pace and Vaque, 1994). Additionally, it is an important food source for the aquatic organisms feeding on zooplankton ...

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