Abstract: Phytoplankton is an important component of wetland ecosystems. Changes in the quantity and community structure of phytoplankton may affect the structure and function of wetlands.  The spatial and temporal dynamics of phytoplankton in Haizhu National Wetland Park in winter (2017) and summer (2018) were investigated. Results showed that 171 species belonging to 64 genera in seven phyla were recorded. Chlorophyta, Bacillariophyta and Cyanophyta accounted for 44%, 26% and 13% of all the species, respectively. The dominant species wereMerismopedia cantonensis and Merismopedia minimain both seasons, with Cryptomonas erosa being also among the dominant species in winter. The community structure, cell density and biodiversity index of phytoplankton varied significantly between seasons. In winter, the community was dominated by bacillariophyta and chlorophyta, accounting for 32% and 29% of the phytoplankton; whereas in summer, the community was dominated by cyanophyta, with a 68% contribution. The abundance of phytoplankton in summer was (25.58±18.47) ×10⁶ cells·L^-1, about three times high as that in winter. The Shannon index and Pielou index showed similar trends, being high in winter (4.38 and 0.77) and low in summer (2.92 and 0.51). Spatially, species richness and diversity index were low, but abundance was high in Haizhu Lake. The abundance of bacillariophyta was the highest in the wetland of Tang River and Xijiang River, while other sites were dominated by cyanobacteria. Total nitrogen and temperature were important factors affecting the phytoplankton community structure. Our results are useful for management and protection of Haizhu National Wetland Park.

Key words: leafing intensity, leaf number, twig diameter., leaf area, twig length