With the accelerated urbanization and rapid development of the industrial and agricultural sectors, concern about the pollution of water environments is becoming more widespread. Algal blooms of varying sizes are becoming increasingly frequent in lakes and reservoirs; temperatures, nutrients, heavy metals, and dissolved oxygen are the factors that influence algal bloom occurrence. However, knowledge of the combined effect of heavy metals and temperature on algal growth remains limited. Thus, this study investigated how specific concentrations of heavy metals affect algal growth at different temperatures; to this end, two heavy metals were used (0.01 mg/L Pb²⁺ and 0.05 mg/L Cr⁶⁺) at three incubation temperatures (15, 25, and 30 °C) with the alga Chlorella sp. A higher incubation temperature contributed to a rise in soluble proteins, which promoted algal growth. The density of algal cells increased with temperature, and catalase (CAT) decreased with increasing temperature. Chlorella sp. growth and catalase activity were optimal at 30 °C (algal cell density: 1.46 × 10⁷ cell/L; CAT activity: 29.98 gprot/L). Pb²⁺ and Cr⁶⁺ significantly promoted Chlorella sp. growth during incubation at 25 and 30 °C, respectively. At specific temperatures, 0.01 mg/L Pb²⁺ and 0.05 mg/L Cr⁶⁺ promoted the production of soluble proteins and, hence, the growth of Chlorella sp. The results provide a useful background for the mitigation and prevention of algal blooms.

Microplastics (MPs) synergistically interact with heavy metal contaminants, posing substantial ecological threats to biota. Hydrodynamic regimes and water-level fluctuations within the Three Gorges Reservoir (TGR) critically influence contaminant dynamics. Nevertheless, biomolecular responses to MP and heavy metal co-exposure at protein and enzymatic levels remain inadequately characterized. This study selected polyethylene (PE), polypropylene (PP), and lead(II) ions (Pb2+) to examine the freshwater microalgae Chlorella vulgaris within the TGR. After 96 h of exposure, the half-maximal effective concentrations for PE and PP against C. vulgaris were determined to be 334 mg/L and 295.29 mg/L, respectively. PE, PP, and Pb2+ significantly reduced the accumulation of C. vulgaris biomass, deteriorated algal cell growth, and caused the algal cells to undergo membrane lipid peroxidation. Nitrate and phosphate assimilation were considerably inhibited across all treatments, with heightened suppression under co-exposure. MPs’ addition significantly increased malondialdehyde levels. MP adsorption of Pb2+ appeared to attenuate Pb2+-associated changes in nitrate reductase (NR) and alkaline phosphatase activities. This study provides a theoretical foundation for evaluating MP and heavy metal ecological risks in reservoir ecosystems.