| Lake Dianshan is famous for flowing with milk and honey, and has the water sources, fish farming, and recreation function. In recent decade, the water quality of Lake Dianshan is declining and eutrophication is more serious. That attracted wide attention. From June 2009 to June 2010, we monitored 12 monitoring points 16 times for knowing the water quality, the change of phytoplankton species composition, density variation, the correlation between phytoplankton and environmental factors, and did the dynamic studies for knowing the growth of phytoplankton. The main results as follows:1. A total of 8 phylum,89 genera,285 species of phytoplankton were identified (with varietas). That includes Chlorophyta(43 genera 135 species), Bacillariophyta(18 genera 58 species), Euglenophyta(5 genera 34 species), Cyanophyta(9 genera 32 species), Cryptophyta(4 genera 8 species),Chrysophyta(4 genera 8 species), Pyrrophyta(3 genera 7 species), Xanthophyta(3 genera 3 species).The dominated species were Chroomonas acuta, Chlorella vulgaris, Ulothrix flaccidum, Synedra acus, Melosira ambiuga Microcystis, Oscillatoria mainly. Lake Dianshan is in eutrophication currently, and has the trend to be heavy eutrophication.2. Number of phytoplankton species in Lake Dianshan had relevance with distribution of monitoring points. Area around outlet had more phytoplankton species. The season order of species from low to high was autumn, winter, summer, spring. The percentage of phytoplankton species number in different months was different. Except Cyanophyta was the main kind species in summer, the Bacillariophyta was main species in other seasons.3. The mean phytoplankton density was on average 2.19×107cells·L-1 in one year, peak in mid-September 2009. The density order of phytoplankton from low to high was autumn, winter, spring, summer. The point order of mean density from low to high was Lake Yuandang, lake central, lake east, lake west, (equal to lake north), lake south. The lowest density point was Lake Yuandang, the highest point was the No.1 point. The phytoplankton density of different points in algae-blooming period was different from non-blooming period, and decided pinots'density order. Lake Dianshan had the furifying function, the phytoplankton density in outlet was lower than inlet. 4. The mean chlorophyll-a was 13.47 mg/m3 on average from May 2009 to June 2010, and ranged from 0.59 to 38.64mg/m3. The season order of chlorophyll-a from low to high was autumn, winter, summer, spring. The change of season was obvious. The points order of chlorophyll-a from low to high was Lake Yuandang, lake central, lake east, lake west, lake south, lake north. The lowest chlorophyll-a point was Lake Yuandang, the highest point was the No.7 point. The average of chlorophyll-a was 23.64 mg/m3, in algae-blooming period, the lowest point was Port Lanlu, the highest point was NO.1 point. The average of chlorophyll-a was 11.85 mg/m3 in non-blooming period, the lowest point was Port Lanlu, the highest point was NO.7 point.5. The correlation between environmental factors and phytoplankton community in year, algae-blooming period was different. The main factors that impact the phytoplankton community in year were as followed:PH, DO, temperature, transparency, dissolved phosphorus, ammonian, TN. The main factors that impact the phytoplankton community in algae-blooming period were as followed:DO, transparency, TP, ammonian, TN. Except DO, transparency, TP, TN, the relationship between others environmental factors and phytoplankton community was declined in algae-blooming period.6. The Microystis aeruginosa grows normally when the concentrations of TN and TP are greater than 4.0 mg-L-1,0.50mg-L-1 respectively. The optimum concentration ranges of TN and TP for the growth of Microystis aeruginosa are 16.0～64.0 mg-L-1 and 1.5.0～5.40 mg-L-1 respectively. KsN is higher than Ksp, which indicates that the affinity of TP to Microystis aeruginosa is higher than TN.7. The Scenedesmus quadricauda grows normally when the concentrations of TN and TP are greater than 4.0 mg·L-1.0.20 mg-L"1 respectively. The optimum concentration ranges of TN and TP for the growth of Scenedesmus quadricauda are16,0-32.0 mg-L-1 and 2.0～5.40 mg-L-1 respectively. KsN is higher than Ksp, which indicates that the affinity of TP to Scenedesmus quadricauda is higher than TN.
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