Abstract: To understand the assembly process and diversity dynamics of eukaryotic plankton community during the water transfer period at the first section of the Yellow River-to-Qingdao Water Diversion Project and to explore the influence of environmental factors, 18S rRNA gene high-throughput sequencing technology was used to analyze the diversity index and community structure of eukaryotic plankton. We further explored the relationships between the distribution characteristics of eukaryotic plankton and environmental factors and revealed the interactions and community assembly process of eukaryotic plankton. The results showed that the eukaryotic plankton community structure varied among different locations and months. The abundance, diversity, and evenness of the eukaryotic plankton communities in the Yellow River water were greater than those in the Yangtze River water in the East Route of the South-to-North Water Diversion. After the confluence, the diversity and evenness of eukaryotic plankton communities increased, and their abundance decreased. The dominant eukaryotic plankton species were the SAR super-group, Cryptophyta, Chlorophyta, Cryptomycota, and Arthropoda. The main environmental factors affecting the eukaryotic plankton community were water temperature, dissolved oxygen, pH, and ammonium. The eukaryotic plankton community was dominated by cooperative and mutualistic relationships as shown by the co-occurrence network. The eukaryotic plankton communities were influenced mainly by stochastic processes in January, April and June, and by deterministic processes in May.

Key words: Yellow River-to-Qingdao Water Diversion Project, eukaryotic plankton, community structure, assembly process