Assessment of the phytoplankton diversity and its temporal dynamics in the freshwater ecosystem of the Beni-Zid dam, Algeria

<p style="line-height:200%;margin-bottom:0cm;tab-stops:109.55pt;text-align:justify;"><span style="font-family:"Times New Roman",serif;font-size:12.0pt;line-height:200%;" lang="EN-US">The temporal variability of diversity and cell abundance of the phytoplankton community was studied in the Beni-Zid reservoir using the Utermöhl method. A total of 54 taxa were identi</span><span style="font-family:"Times New Roman",serif;font-size:12.0pt;line-height:200%;">fi</span><span style="font-family:"Times New Roman",serif;font-size:12.0pt;line-height:200%;" lang="EN-US">ed, belonging to seven classes: Chlorophyceae (17 taxa), Bacillariophyceae (15 taxa), Cyanophyceae (14 taxa), Zygnematophyceae (4 taxa) Cryptophyceae (2 taxa), Dinophyceae (1 taxon), and Chrysophyceae (1 taxon). Throughout the study period, perennial species were </span><em><span style="font-family:"Times New Roman",serif;font-size:12.0pt;line-height:200%;" lang="EN-US">Oscillatoria limnetica</span></em><span style="font-family:"Times New Roman",serif;font-size:12.0pt;line-height:200%;" lang="EN-US">, </span><em><span style="font-family:"Times New Roman",serif;font-size:12.0pt;line-height:200%;" lang="EN-US">Microcystis aeruginosa</span></em><span style="font-family:"Times New Roman",serif;font-size:12.0pt;line-height:200%;" lang="EN-US">, </span><em><span style="font-family:"Times New Roman",serif;font-size:12.0pt;line-height:200%;" lang="EN-US">Pinnularia major </span></em><span style="font-family:"Times New Roman",serif;font-size:12.0pt;line-height:200%;" lang="EN-US">and</span><em><span style="font-family:"Times New Roman",serif;font-size:12.0pt;line-height:200%;" lang="EN-US"> </span></em><span style="font-family:"Times New Roman",serif;font-size:12.0pt;line-height:200%;" lang="EN-US"> </span><em><span style="font-family:"Times New Roman",serif;font-size:12.0pt;line-height:200%;" lang="EN-US">Dinobryon sp. </span></em><span style="font-family:"Times New Roman",serif;font-size:12.0pt;line-height:200%;" lang="EN-US">The highest cell densities were 585.10<sup>4</sup> Ind.l<sup>-1 </sup>recorded during June, with quantitative dominance of Cyanophyceae. The highest diversity and a quasi-homogeneous distribution of cells enumerated on the different inventoried classes were observed during the period from March to June; this is indicated by the maximum values of the evenness index of Pielou (</span><em><span style="font-family:"Times New Roman",serif;font-size:12.0pt;line-height:200%;" lang="EN-US">J</span></em><span style="font-family:"Times New Roman",serif;font-size:12.0pt;line-height:200%;" lang="EN-US">) and the Margalef index (D<sub>m</sub>). </span><span class="fontstyle21" style="font-family:"Times New Roman",serif;font-size:12.0pt;line-height:200%;" lang="EN-US">The monthly assessment of the water trophic level by calculating the trophic state index (TSI), </span><span style="font-family:"Times New Roman",serif;font-size:12.0pt;line-height:200%;">indicates an eutrophic state of the dam water. It confirms the tendency for blue-green algae to dominate the existing phytoplankton community. The Hierarchical Cluster Analysis (HCA) and the principal components analysis (PCA) both applied to the data of deviations calculated between the different TSIs, showed a strong correlation between the reduction of water transparency by planktonic microalgae cells and the limitation of its growth by the phosphorus element, this particularly concerns the period of the year from August to November. While nitrogen element limitation hardly occurred at any time of the year.</span></p>