An investigation on phytoplankton was conducted in theHarbin section of SonghuaRiver during June (wet season ) , August (normal season) and October (dry season) in 2011 bysetting up seven systematically placed sample stations.We identified a total of 125 species, of which 55 were Bacillariophyta, 51 were Chlorophyta, 11 were Cyanophyta and 8 were other species.The phytoplankton abundance changes significantly in different hydrological period, and the order is the dry season (6951.6×104ind./L)>normal season( 3556.8×104ind./L)>wet season (2059.2×104 ind./L).We applied ca-nonical correspondence analysis (CCA) to explore the relationship between phytoplankton composition, distribution and environmental factors, and used biodiversity index to evaluate water quality.Shannon-weaver index, Pielou index and Mar-galef index in dry season are lower than those of wet season and normal season, so the water quality is relatively poor, and 2# right, 4#right and 6#middle are polluted in serious levels in dry season.By CCA, the water temperature and distribu-tion are the main factors affecting the distribution of phytoplankton community.The biochemical oxygen demand and total phosphorus are also significantly positively correlated with the phytoplankton species distribution.%于2011年丰水期（6月份），平水期（8月份）和枯水期（10月份）对松花江哈尔滨段浮游植物进行调查，共监测到浮游植物7门125种及变种；其中硅藻55种，绿藻51种，蓝藻11种，其他8种。不同水文期浮游植物丰度（以液体中生物个体数量计）变化明显，枯水期（6951．6×104个/L）＞平水期（3556．8×104个/L）＞丰水期（2059．2×104个/L）。运用典范对应分析（CCA）及生物多样性指数对浮游植物组成、分布及其与环境因子的关系进行了分析和水质评价。结果表明，枯水期shannon-weaver 指数、Pielou指数和Margalef 指数比丰水期和平水期低，水质相对较差，其中2＃右、4＃右、6＃中处于重污染。典范对应分析显示，水温和浊度是影响浮游植物分布格局的重要环境因子，化学需氧量和总磷也和浮游植物分布有显著的相关性。
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