Abstract: In order to study the ecological niche and interspecies association of dominant phytoplankton species after impounding of Wuxikou Water Conservancy Project in Changjiang River Basin, phytoplankton samples from nine sampling sites were studied in three different water situation periods in March(normal period), June(wet period) and November(dry period) 2021. The results showed that there were 27 dominant phytoplankton species in 4 phyla. Among them, Melosira granulata was the dominant species in all three situation periods, divided into widespread species. The appearance of Dinobryon divergens in November indicated that the water quality was οs type, showing a dynamic of poor nutrition, but the watershed in moderate condition. According to the niche breadth and niche overlap index of the dominant species, they were divided into three species with different resource utilization abilities. In addition, according to the results of statistical test, phytoplankton showed a significant positive correlation. The association was significant in 11 pairs. The significant rate of association was 6.18%. This may be due to the effect of water storage on phytoplankton species diversity, which makes the community structure in the early and middle stages of development.

Key words: phytoplankton, niche breadth, niche overlap, interspecific association