中文摘要：

于2009年12月、2010年1月和2月对广东省大沙河水库湖泊区距水表层0．5m、5m和10m三个水层的浮游植物进行了定性与定量分析，同时对环境变量进行了测定。采样期间三个月的总降雨量为263mm，水温范围在15．5-19．4℃之间，水体处于混合状态。三次采样中，共检测出浮游植物69种（属），隶属于6个门，浮游植物丰度范围在4．1×10^6-14．8×10^6cells·L^-1之间。三个水层的浮游植物优势种类差异不显著（p〉0．05），丰度的主要优势种为蓝藻门的卷曲鱼腥藻（Anabaena circinalis）、铜绿微囊藻（Microcystis aeruginosa），这两个种的丰度之和占总丰度的70％以上，在2009年12月和2010年2月的表层出现了轻度鱼腥藻和微囊藻水华。蓝藻自身的浮力调节机制和适应低磷的生活策略是其成为优势种的重要原因，相对稳定的外部条件、水体混合与富营养共同导致的光的可获得性的减少是形成蓝藻水华的关键外部因子。

英文摘要：

Phytoplankton communities at the water depth of 0.5, 5, and 10 m were investigated in the lacustrine zone of DashaheReservoir in the winter from December, 2009 to February, 2010. Total precipitation in the three months was 263 mm; temperature ranged from 15.5 ℃ to 19.4 ~C; the water column was fully mixed. Sixty four species of phytoplankton belonging to six phyla were identified. Total phytoplankton abundance ranged from 4.1×10^6 to 14.8×10^6 cells＇L^-1. There was no significant difference in the dominant phytoplankton species at the three water layers. Anabaena circinalis and Microcystis aeruginosa were the predominant species, and contributed to about 70% of total abundance in all of the sampling periods at all depths. Anabaena and Microcystis blooms slightly occurred in the December of 2009 and February of 2010. The regulating buoyancy of cyanobacteria, as well as low availability of phosphorus and light led to the dominance of the two species.