Seasonal dynamics of phytoplankton and its relationship with the environmental factors in Joumine reservoir, Tunisia

In the last decades, the frequency of dry years has increased significantly due to the lack of rainfall. Added to that, demographic growth, anthropogenic activities, and intensive agriculture impact the quality of water bodies and induce their eutrophication by the proliferation of phytoplankton. Therefore, managing water quality and ensuring its sustainability in the future is challenging. The Joumine reservoir, situated in the northwestern part of Tunisia, is part of the main master plan for water transfer. It is mainly used for drinking and irrigation purposes. This reservoir is affected by eutrophication. The proliferation of phytoplankton depends on many factors and their dynamics. These include physical, chemical and biological factors. Within this context, the main objective of this study is to asses the influence of environmental parameters over the phytoplankton’s dynamic. Water measurement and sampling was conducted at 8 stations in order to cover the spatiotemporal variability of water quality parameters covering the water plan during May, June, August, October during 2021 and March and June in 2022. These measurements included concentrations of physical, chemical parameters, Chlorophyll a (Chla), as well as the quantification and the identification of species. A total of 25 species of phytoplankton belonging to 7 algal classes were identified, predominately Chlorophyceae (44%) followed by cyanobacteria (24%), Diatoms and euglenophyceae representing respectively 12% and 8% of all identified taxa other taxa as Dinoflagellates , Klebsormidiophycae and cryptophycae appear very irregularly ,each taxa represent 4% respectively. The phytoplankton biovolume averaged 3.34 µm3/l. Phytoplankton community structure and water quality variables changed substantially over the survey period. Redundancy analysis showed that NO3-, NH4+, Dissolved oxygen, pH and water temperature were the primary influencing factors for the phytoplankton community distribution. These results will allow us to model the dynamic of cyanobacteria in the Joumine reservoir and improve the early warning among cyanobacteria blooms.