Abstract: Investigations on phytoplankton of Jiaojiang Estuary（28.67°~28.69°N, 121.45°~121.62°E） were carried out in July 2007, July 2008, and August 2010, and compared with historical data. 5 Phylums and 167 species were identified in the three investigations which were 101, 96 and 117 respectively before，inning and after reclamation. Cell abundance of phytoplankton were 20.34×10³ cell /L, 266.94×10³ cell /L and 66.94×10³ cell /L, and Shannon-Wiener Index of phytoplankton were 1.95, 0.60 and 0.40 respectively. Dominant species of phytoplankton included Bacillariophyta and Pyrrophyta before and after reclamation, such as Coscinodiscus jonesianus, Coscinodiscus radiatus, Skeletonema costatum, Rhizosolenia delicatula, but only Bacillariophyta existed inning reclamation, such as Chaetoceros lorenzianus and Ditylum brightwellii. Reclamation promoted the enhancement of cell abundance but reduced the stability and balance of phytoplankton community structure. CCA analysis showed that pH, temperature, nitrogen/phosphorus/silicon nutrients, dissolved oxygen and chemical oxygen demand were the main water quality parameters affecting community structure of phytoplankton. The main water quality parameters affecting Chlorophyta, Bacillariophyta, Cyanophyta and Pyrrophyta were dissolved oxygen, oil, temperature and chemical oxygen demand respectively. Long time scale and short time scale analysis come to similar conclusions that water quality , community structure and biodiversity of phytoplankton have changed before and after reclamation of Jiaojiang Estuary.

Key words: phytoplankton, community structure, biodiversity, reclamation, Jiaojiang Estuary