Effects of Physicochemical Parameters and Some Heavy Metals on the Distribution of Phytoplankton in Lake Oubeira

Our study focused on the effects of various physical and chemical parameters, along with certain heavy metals, on the spatiotemporal distribution of phytoplankton in Lake Oubeira from January 2021 to January 2022. Monthly sampling of phytoplankton, along with measurements of specific physicochemical parameters and heavy metals, was conducted at two stations characterized by distinct physico-chemical properties. All data analyses in this study were performed using R, version 4.0.1 (R Core Team 2020). The observations of the morphological and anatomical characteristics of phytoplankton collected from Lake Oubeira allowed us to identify 48 genera belonging to five classes: Cyanophyceae, Bacillariophyceae, Chlorophyceae, Euglenophyceae, and Dinophyceae. Notably, there was a dominance of cyanophytes, with 9 toxic genera identified. The measured levels of heavy metals such as lead (Pb), cadmium (Cd), and mercury (Hg) in Lake Oubeira’s waters revealed significant spatiotemporal variation. The highest concentrations of these heavy metals were recorded during the summer, while the lowest values were observed in autumn. An in-depth principal component analysis (PCA) considering both "station" and "season" factors indicated a spatiotemporal variation between several parameters, including pH, dissolved oxygen (O₂), Pb, Cd, and the density of certain phytoplankton taxa (Euglenophyceae, Dinophyceae, Bacillariophyceae, and Chlorophyceae). Our findings show that during summer, the waters of Lake Oubeira are warm, alkaline, and less oxygenated, with a high abundance of Euglenophyceae taxa. In contrast, spring conditions are characterized by cooler, well-oxygenated waters with a richness of Dinophyceae, Bacillariophyceae, and Chlorophyceae taxa. During winter, the waters are cold, less alkaline, and less oxygenated.