Résumé: Although several studies have been conducted to investigate the dynamics of cyanobacteria, their toxicity, and the environmentalfactors that influence their proliferation in North African freshwater ecosystems, our current understanding is limited. Thisstudy focuses on the spatiotemporal dynamics of cyanobacteria in the Zit-Emba reservoir, as well as the role of environmentalvariables. From March 2015 to February 2016, sampling was conducted at four sampling points (S1-S4). The co-occurrenceof two bloom-forming cyanobacteria, Microcystis and Woronichinia, as well as their rapid growth in autumn (9 × 104 cells.mL−1 and 8 × 104 cells.mL−1, respectively), was an unexpected phenomenon. Woronichinia is a little-studied cyanobacterium,with most reports coming from Europe and North America. During the monitoring period, microcystin levels ranged from0.04—5.74 μg.L−1, with peaks observed during the cyanobacteria bloom. The PCA and correlation results revealed that watertemperature and nutrient loading, particularly P-PO4 (max = 0.4 mg.L−1), were the most important contributing variables. Thisstudy emphasizes the importance of regularly monitoring cyanobacteria and their toxins, as well as implementing watershedmanagement to reduce nutrient inputs in freshwater sources used for drinking water supplies.

Résumé: Massive cyanobacteria blooms have become a worldwide concern problem due to the multiple nuisances they can cause. The impacts of climate change are distinct from other environmental constraints controlling its population dynamics. The current study was accomplished in the monomictic reservoir Hammam Debagh (North-Eastern Algeria). A sampling campaign was conducted during May and June 2012 in four surface sampling stations and the water column in the center of this reservoir. This study aims to investigate the surface bloom of Planktothrix rubescens (De Candolle ex Gomont 1892) Anagnostidis and Komarek, 1988; observed for the first time in an Algerian reservoir with a focus on the environmental variable changes in 2012. During this thick epilimnetic bloom, P. rubescens spread in all water column layers, reaching 6.4 x 106 cells mL-1 at 2m from the surface recorded on 11.05.2012. Meanwhile, at the surface P. rubescens abundances ranged from 3 x 105 to 3.6 x 106 cells mL-1. The biomass was so high that the signal from the phycocyanin probe became saturated attending a value of 200 μg L-1 PC in the top 1 m. In addition, the biogenic compounds especially P-PO4 and NO3 show a high concentration of 0.48 mg L-1 and 5 mg L-1 respectively. The red pigmented cyanobacterium bloom altered environmental conditions in the reservoir Hammam Debagh, since primarily oxygen concentration shows a minimum of 2.63 mg L-1 and water transparency did not exceed 1m (min= 40cm). The vertical profile of temperature performed on 29.05.2012 over 33m; shows a stratified water column ranging from 22.6°C in the upper subsurface to 9.8°C in the bottom hypolimnion. Finally, suitable meteorological conditions were observed during 2012.

Résumé: This study aims to identify the C. raciborskii species based on its morphology, examine its morphological variability by tracking its annual life cycle and environmental parameters fluctuations, and assess its toxicity by measuring cylindrospermopsin (CYN) in Lake Oubeira between October 2021 and September 2022. Microscopic observations revealed the existence of straight or slightly curved filaments. Filament ends exhibited various shapes: rounded (39%), intermediate (40%), pencil (16%), and needle (5%). However, only rounded filament ends were present throughout this cycle. Four morphotypes were observed: filaments with heterocytes and akinetes (< 1%), akinetes only (< 2%), heterocytes only (6%), and neither heterocytes nor akinetes (> 90%). Results showed that filaments without heterocytes or akinetes, and those with only heterocytes, positively correlated with nitrates, conductivity, turbidity, atmopspheric temperature, water temperature, and pH, but negatively with transparency and dissolved oxygen. Conversely, filaments with heterocytes and akinetes were positively correlated with precipitation (Preci) (p ≤ 0.001), showing a positive correlation with phosphates while filaments with only akinetes displayed negative correlations with WT and Trans. Only extracellular Cylindrospermopsin was detected during the study period, excluding February and April, with concentrations ranging from 80 to 750 ng/. Four CYN peaks exceeding 500 ng/L were offset from C. raciborskii biomass peaks. The observed morphological variability in filaments sampled from Lake Oubeira confirms the species as C. raciborskii. However, employing additional approaches, such as culturing, and molecular taxonomy, would be necessary to complete the study of this cyanobacteria species.

Résumé: 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 North-East 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 NO3-N, NH4-N, and NO2-N. This demonstration of toxigenic cyanobacteria in this drinking water production dam involves regular monitoring of the cyanobacterial communities and cyanotoxins in raw water.

Résumé: This study investigated the bacteriological and physicochemical quality of seawater and sediment samples collected from four sampling sites in the Gulf of Annaba (Northeastern Algeria) over a one-year period. Culture-based techniques were used to quantify and assess Fecal Indicator Bacteria (FIB) and potentially pathogenic bacteria. Additionally, various physicochemical parameters including temperature, pH, salinity, dissolved oxygen, and suspended solids were measured. The results revealed seasonal variations in the physicochemical variables, reflecting the influence of environmental conditions in the research area. The highest concentrations of FIB were observed in samples obtained from Sidi Salem and Rezgui Rachid, indicating a possible association with sewage contamination. Furthermore, the sediments collected from all sites exhibited higher levels of FIB and potentially pathogenic bacteria compared to the seawater samples, particularly during the summer and fall seasons.

Résumé: Caused by excess levels of nutrients and increased temperatures, freshwater cyanobacterial blooms have become a serious global issue. However, with the development of artificial intelligence and extreme learning machine methods, the forecasting of cyanobacteria blooms has become more feasible. We explored the use of multiple techniques, including both statistical [Multiple Regression Model (MLR) and Support Vector Machine (SVM)] and evolutionary [Particle Swarm Optimization (PSO), Genetic Algorithm (GA), and Bird Swarm Algorithm (BSA)], to approximate models for the prediction of Microcystis density. The data set was collected from Oubeira Lake, a natural shallow Mediterranean lake in the northeast of Algeria. From the correlation analysis of ten water variables monitored, six potential factors including temperature, ammonium, nitrate, and ortho-phosphate were selected. The performance indices showed; MLR and PSO provided the best results. PSO gave the best fitness but all techniques performed well. BSA had better fitness but was very slow across generations. PSO was faster than the other techniques and at generation 20 it passed BSA. GA passed BSA a little further, at generation 50. The major contributions of our work not only focus on the modelling process itself, but also take into consideration the main factors affecting Microcystis blooms, by incorporating them in all applied models.

Résumé: Actually, harmful cyanobacterial efflorescence in Algerian water bodies used for drinking water are dominant throughout the year and their management requires a better knowledge of the cyanobacteria dynamics and the environmental parameters related to their dominance. The Ain Zada reservoir is a home of 5 genera. Occurrence frequency estimation of the identified genera shows the constancy of Planktothrix, the regularity of Aphanizomenon, Pseudanabaena and Cylindrospermopsis and the rarity of Oscillatoria. The dominating genus Planktothrix is represented exclusively by Planktothrix agardhii ; This species showed the highest proportion rates in winter (95.61 %), spring (94.80 %) and autumn (80.29 %) and the lowest in summer (29.16 %). Planktothrix agardii abundances show positive relation with suspended solids and chlorophyll a and negative relation with the depth of Secchi disc. Blooms of the potential toxinogenic Planktothrix agardhii and Cylindrospermopsis are related negatively. Results from cyanotoxins and pigments characterization showed a strong positive relation of Planktothrix agardhii abundance with microcystins (MCs) and phycocyanin (PC) concentrations. Indeed, in Ain Zada dam, we found that MCs contents have positive relation with water temperature and pH and negative relation with NO3. Our results show that, except for the months of March, October and November, the monthly abundances of cyanobacterial population recorded in Ain Zada dam exceeded the alert level 2. The filamentous species found in this dam are of great concern they are able to synthesize toxins harmful to aquatic and terrestrial organisms. Further research is needed to confirm the presence of other cyanotoxins (e.g. cylindrospermopsin) in Ain Zada dam.

Résumé: Harmful cyanobacterial eforescence 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 North-East of Algeria, was constructed to provide drinking water, irrigation, and fshing. The vertical and seasonal distribution variation of cyanobacteria community associated with environmental factors was comprehensively investigated from April 2016 to December 2016 at fve depths, based on a seasonal sampling. The cyanobacteria communities of this reservoir are composed of seven genera belonging to fve 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 profle 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, NH4-N, and NO2-N. This demonstration of toxigenic cyanobacteria in this drinking water production dam involves regular monitoring of the cyanobacterial communities and cyanotoxins in raw water. Keywords: Cyanobacteria community, Zit-Emba reservoir; environmental variables; dynamics; Algeria.

Résumé: Succession in bloom-forming cyanobacteria belonging to distant functional groups in freshwater ecosystems is currently an undescribed phenomenon. However in the Hammam Debagh reservoir (Algeria), P. rubescens and Microcystis sp. co-occur and sometimes proliferate. With the aim of identifying the main factors and processes involved in this unusual cohabitation, water samples were collected monthly from February 2013 to June 2015 at the subsurface at four sampling stations and along the entire water column at one sampling station. In addition, the composition of the cyanobacterial communities was estimated by Illumina sequencing of a 16S rRNA gene fragment from samples collected over one year (October 2013-November 2014). This molecular approach showed that the Hammam Debagh reservoir displays high species richness (89 species) but very low diversity due to the high dominance of Microcystis in this community. Furthermore, it appears that Planktothrix rubescens and Microcystis sp. coexisted (from September to January) but proliferated alternately (Spring 2015 for P. rubescens and Spring 2014 and Autumn 2014/2015 for Microcystis). The main factors and processes explaining these changes in bloom-forming species seem to be related to the variation in the depth of the lake during the mixing period and to the water temperatures during the winter prior to the bloom season in spring.