Spatiotemporal Distribution Characteristics and Driving Factors of Phytoplankton in the Mainstream of the Yellow River (Shandong Section)

To investigate the spatiotemporal distribution of phytoplankton communities and their major environmental influences in the mainstream of the Yellow River (Shandong section), 29 sampling sites were surveyed in the summer and autumn of 2022 and the spring of 2023. Among the 206 phytoplankton species belonging to 8 phyla and 99 genera, Bacillariophyta, Chlorophyta, and Cyanobacteria were the main dominant groups, and Aulacoseira granulata var. angustissima (O.Müller) Simonsen, Fragilaria capucina Desmazières, and Ulnaria acus (Kützing) Aboal were the most important dominant species. The number of phytoplankton species and cell densities exhibited significant seasonal changes in the sequence of summer > autumn > spring. The phytoplankton community underwent a succession from Bacillariophyta–Chlorophyta dominance in spring and summer to Bacillariophyta–Cyanobacteria dominance in autumn. Water temperature, dissolved oxygen, and transparency were the most important factors affecting the growth of the dominant Bacillariophyta species. The spatiotemporal distribution of phytoplankton is jointly regulated by multiple environmental factors, providing a scientific basis for the evaluation and management of regional aquatic ecosystems.