Heavy Metals Exacerbate the Effect of Temperature on the Growth of Chlorella sp.: Implications on Algal Blooms and Management

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.