Cyanobacteria dynamics and Microcystins: an emphasis on late autumn mass development of Woronichinia and Microcystis in the Reservoir Zit-Emba, North-East Algeria

Abstract Despite the available studies on Cyanobacteria dynamics, toxicity, and the incriminated environmental variables in the North African freshwater ecosystems, this is still insufficient. This study focuses on the spatiotemporal dynamic of cyanobacteria in the reservoir Zit-Emba and the role of environmental variables. Sampling was carried out from March 2015 to February 2016 at four sampling points (S1-S4). The cooccurrence of two bloom forming cyanobacteria Microcystis and Woronichia and their massive development in autumn (9x10⁴ cells.mL⁻ ¹ and 8x10⁴ cells.mL⁻ ¹ respectively) was an unexpected phenomenon. Woronichinia is a worldwide poorly studied toxic cyanobacterium reported mainly in Europe and America. Microcystins were detected during the monitoring period (0.04–5.74 µg.L⁻ ¹), and peaks were reported during the cyanobacteria bloom. PCA and correlation results revealed the important role of water temperature and nutrient loading mainly P-PO₄ (max = 0.4 mg.L⁻ ¹) as the most contributing variables. This study highlights the need for regular monitoring of cyanobacteria and their toxins as well as implementing watershed management to reduce nutrient inputs in freshwater sources used for drinking water supplies.