Seasonal Dynamics of Planktonic Algae in the Danjiangkou Reservoir: Nutrient Fluctuations and Ecological Implications

Freshwater reservoirs serve as vital water sources for numerous residential areas. However, the excessive presence of nutrients, such as nitrogen and phosphorus, stimulates rapid algal proliferation, leading to the occurrence of algal blooms. To prevent this phenomenon, it is imperative to conduct regular ecological surveys aimed at assessing water quality and monitoring the dynamic composition of aquatic biological communities within the reservoir’s ecosystem. In this study, seasonal changes in water quality parameters and the spatial and temporal distribution of planktonic algae at 14 sampling sites in the Danjiangkou reservoir were analyzed. A total of 136 taxonomic units of planktonic algae were identified, belonging to 8 phyla, 41 families, and 88 genera, with the dominant algae belonging to the phyla Chlorophyta, Bacillariophyta, and Cyanophyta. The order of abundance of the algae was summer > autumn > spring > winter and Hanku > Intake > Danku > Outflow. WT, pH, DO, CODMn, and Chl a were the primary drivers influencing the changes in the planktonic algal community within the reservoir. Two dominant algae, Chlamydomonas debaryana and Scenedesmus quadricauda, were isolated and cultured indoors to simulate the growth behaviors of algae in the Danjiangkou reservoir. The results show that the growth of C. debaryana was severely limited by the temperature, light, and nutrient concentration, whereas the growth of S. quadricauda was slightly affected under different temperature and light conditions and could occur at low concentrations of nitrogen and phosphorus nutrients. With excess nutrient levels, excessive proliferation of S. quadricauda could potentially cause algal blooms. This study examined the growth characteristics of the dominant algae in the Danjiangkou reservoir under laboratory conditions and delved into their interdependencies with environmental factors, aiming to furnish a theoretical and experimental foundation for investigating algal community dynamics and preventing algal blooms within the freshwater reservoir.