Abstract:Small reservoirs play an important role in both of city and country drinking water supply in the South China. To understand the phytoplankton community dynamics in these small reservoirs, three pumped storage reservoirs and three non-pumped storage reservoirs were investigated in April, August and December, 2006, respectively. 67 and 56 taxa in total were identified in the pumped and the non-pumped storage reservoirs, respectively. Pseudanabaena sp.、Limnothrix redekei、Cylindrospermopsis rackiborskii only appeared in the pumped storage reservoirs, while Cosmarium sp. only occurred in the non-pumped storage reservoirs. Cells abundance and biomass in the pumped storage reservoirs were higher than those in the non-pumped storage reservoirs. The abundance of phytoplankton ranged from 1.25×105 cell L-1 to 4.38×106 cells L-1 in the pumped storage reservoirs, was mainly dominated by cyanobacteria and small cellular chlorococcacean, while the abundance of phytoplankton ranged from 7.1×104 cells L-1 to 4.61×106 cells L-1in the non-pumped storage reservoirs, and dominated by Cosmarium sp.. The biomass of phytoplankton ranged from 2.3 mg L-1 to 8.8 mg L-1 in the pumped storage reservoirs, and from 1.3 mg L-1 to 5.6 mg L-1 in the non-pumped storage reservoirs. The dominant species were seasonally replaced in the pumped storage reservoirs, while those were seasonally constant in the non-pumped storage reservoirs. Water pumped into reservoir made the nutrient distribution and hydrologic processes change, which was a key factor for a significant difference in the structure and dynamics of phytoplankton community between the pumped storage reservoirs and non-pumped storage reservoirs.