| Water is one of the important source of life, agriculture production and base of the ecology. Xiquanyan Reservoir, the second water source place of Harbin, its water ecosystem's state of health needs to be carried on monitoring effectively. The research established 13 sampling stations in Xiquanyan reservoir,9 sampling stations in the reservoir district,4 sampling stations in the upper rivers area stations, and collected water samples from the different water depths in the reservoir district stations. Separately in May, July, August, September and October,2010 sampling, has conducted qualitative and the quantitative investigation to the phytoplankton, simultaneously has carried on the monitor and the analysis to the corresponding water environmental factors. Used the multi-dimensional scaling method to analyze plant plankton's biodiversity and the community structure in the biological statistics, and evaluated the water quality by using abundance, biomass and bio-diversity. Besides, used Canonical Correspondence Analysis (CCA) discussed the correlations among phytoplankton, stations, the environment factors, in order to provide the scientific basis for the Xiquanyan Reservoir's protection and the governance as well as the ecology repair.Total of 7 phyla 345 species were identified, including the reservoir district and upstream rivers area two kind of different water bodies, its respectively identified quantity was 7 phyla 192 species and 6 phyla 122 species. And among which, the majority were Chlorophyta (150) and Bacillariophyta(98), Cyanophyta(56). Which was followed by Euglenophyta (20), Chrysophyta (14), Pyrrophyta (5) and Cryptophyta (2). In the investigated period, altogether has discoveried 47 common species in the Xiquanyan reservoir, which represented by diatom and green alga primarily. And 17 dominant species were found, which represented by diatom primarily. The dominant species has been obviously effected by seasons of summer and autumn, superiority types were few, but the dominant degree was high. However, the dominant species were the most in spring, the dominant degree was low. During summer (Aug.) the Planctonema sp. abundance was the highest, achieved 605.88x105ind./L and autumn (Sep.) the Phormidium allorgei abundance was the highest, achieved 685.44x105ind./L.The temporal and spatial distribution non-uniformity of Phytoplankton's abundance and biomass were remarkable in Xiquanyan reservoir. Analyzing from the seasonal variations, annual average abundance from large to small sorting was: Autumn (Sep.)> summer (Aug.)> summer (Jul.)> autumn (Oct.)> spring (May.); Annual average biomass from large to small sorting was:Summer (Aug.)>autumn (Oct.)>autumn (Sep.)>summer (Jul.)> spring (May.). Analyzing from the spatial distributions, various sampling stations whole year average abundance from large to small sorting was:(a) reservoir district:3#>1#above>1#bottom >4#>2#>7#middle>8#middle>6#bottom>9#above >9#middle>7#bottom>8#bottom>9#bottom>5#bottom. (b) upstream rivers area:13#>12#>11#>10#; Annual average biomass from large to small sorting was:(a) reservoir district:7#middle>3# >1#bottom>1#above>8#middle>6#middle>4#>2#>5#above>9#middle>#9above>8#above>7#above>6#above >5#middle>6#bottom>9# bottom>7#bottom>8#bottom>5#bottom;(b) upstream rivers area:13#>12#> 11#>10#·Regardless of being the abundance or the biomass, in the whole the reservoir district is higher than the upstream rivers area.The calculation result was: the blue-green algae and the green algae to absorb the N element month average value respectively were 858.1148 mg/m3 and 520.1001mg/m3. The blue-green algae absorbed N element 1.741 g/m3 in summer (July), which was greatest. And the green alga absorbed N element 1.711 g/m3 in summer (August), which reached greatest. Calculating from the whole year to the N element's absorbing capacity, the blue-green algae and the green algae respectively was 10.297 g/m3 and 6.241 g/m3. Looking from the whole year to the P element's absorbing capacity, the blue-green algae and the green algae respectively was 1.471 g/m3 and 0.892 g/m3. The whole year to the C element's absorbing capacity of the blue-green algae and the green algae respectively was 58.842 g/m and 35.664 g/m3.In the investigation period, Xiquanyan reservoir's Shannon-Wiener index of phytoplankton bio-diversity indexes was between 2.19～4.78, Pielou index between 0.41-0.97, and Margalef index between 2.54～7.82 of whole year. The temporal and spatial distributions of phytoplankton's bio-diversity indexes were remarkable. Analyzed from the seasonal distributions, the Shannon-Weaver index changed tendency was basically corresponding with the Pielou index change, which was spring (May.) highest, the next was the autumn (Oct.), summer (Aug.) lowest, but the Margalef index was the autumn (Oct.) highest, next was the autumn (Sep.), summer (Jul.) lowest. Analyzing from the spatial distributions of whole year, the Shannon-Wiener index's maximum and the minimum values appeared separately in the autumn (Oct.) the 12# and the summer (Aug.) 9#middlc; the Pielou index's maximum and the minimum values appeared separately in the spring (May) 6#middle and the in the autumn (Sep.) 2#; the Margalef index's maximum values appeared in the autumn (October) 9#above, and the minimum values in the summer (Jul.) on 5# and the summer (Aug.) 8#bottom. The results of correlation analysis, three indices mutually remarkable related, may express the Xiquanyan reservoir phytoplankton's bio-diversity well. Carrying on Multidimensional scaling analysis to the phytoplankton community, it divided all stations in the Xiquanyan Reservoir into the reservoir ecosystem and the rivers ecosystem parts. Simultaneously, it divided the reservoir district's stations into the rivers'warehousing mouth place, the reservoir center and the dam mouth place three parts, which conformed to the actual state. May demonstrated between clearly various stations by the MDS distribution charts phytoplankton community's distance (i.e. similarity), simultaneously also indicated that various sites phytoplankton community composition existed obviously different.The results of Canonical Correspondence Analysis respected that, water temperature and nutrient loading became mainly driving factors of the Xiquanyan reservoir phytoplankton's community structure dynamic state. In spring, water temperature, dissolved oxygen and conductance rate were remarkable correlations with Axis 1, for main contribute variables. But in summer and autumn, NO3-N, NH4-N, depth, SD, DO,TN and TP were remarkable correlation with Axis 1, for main contribute variables. The ordination of phytoplankton main species' abundance revealed an apparently dynamic changeable character, Cyanophyta, Chlorophyta and Eulenophyta mainly under the impact of nutrient concentration and water temperature, but Bacillariophyta, Chrysophyta and Cryptophyta were remarkable correlation with water temperature, SD, DO and depth. Moreover, nutrient concentration was one of phytoplankton mainly influencing factor, firstly was its concentration higher, satisfied to the demand of phytoplankton's growth. Secondly, TN/TP was suitable to be favor for the growth of Cyanophyta, which caused high abundance of Cyanophyta and Chlorophyta. Therefore, it suggests that comprehensive treatment should be adopted to control the excessive input of nutrient, mainly control the input of outside source N, P.
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