The Characteristics Of Phytoplankton Community And Ecological Modelling Analysis For Wuliangsuhai Lake In Inner Mongolia

Phytoplankton is the most important primary productivity and bait of fish, the basis of the food-chain, plays an very important role on materials circulation and energy flow of ecological system. Phytoplankton has small individual, fast breeding, various species, large quantity, wide distribution and extremely sensitive to change of environment. The change of phytoplankton community structure can cause change recirculation of nutrients and instability of ecosystem, even causing outbreak of algal bloom and collapse of ecosystem.This paper, based on the investigation of phytoplankton community, study seasonal and spatial variation of phytoplankton species, abundance, biomass, diversity index, functional group, the classification of phytoplankton community structure and distribution of dominant species and influence for environmental factors on major species and functional group. To simulate change of main pollutants and succession of large aquatic plants, phytoplankton and zooplankton in lake and the response relationship between the inflow water quality of reduction and water quality and phytoplankton biomass of lake, using multivariate statistical methods, redundancy analysis RDA model, self-organizing feature map neural network model and AQUATOX ecological model. The main findings are listed as below:(1) The results shown that there are110genera,7phyla and281species of phytoplankton with dominated Chlorophyta including126species of47genera. We also found25genera and46species of Bacillariophyta,22genera and46species of Cyanophyta,9genera and30species of Euglennophyta,4genera and8species of Chrysophyta,2genera and4species of Cryptophyta,1genera and3species of Pyrrophyta. Phytoplankton species (genus) was significantly higher in summer than other seasons.The main species were composed of Chlorophyta, Bacillariophyta and Cyanophyta. The number of Green species is more than diatom and the number of diatom species is more than cyanobacteria. In2012, Phytoplankton abundance and biomass was the highest in spring, while in2011and2013, it was the highest in summer. Chlorophyta, Bacillariophyta and Cyanobacteria were the main composition groups of phytoplankton community in every period.(2) The multi-dimensional scaling analysis shown that phytoplankton community could be classified as the influent community in the north, deep purification community in the south, hydrostatic community in the north along the coast, retention community in the central part of the lake. (3) The correlation of phytoplankton abundance and biomass and water was significant statistically. The line eequation wasy=0.764x+14.24. The correlation of phytoplankton abundance and biomass and TN was significant statistically. The line eequation was. The correlation y=5.06x+14.96of phytoplankton abundance and biomass and TP(≤0.2mg/L) was significant statistically. The line equation was y=136.64x+16.92and.y=128.15x+13.62.(4) Phytoplankton community is divided into eight types by using SOM neural network: Ⅰ:Dactylococcopsis+Merismopedia+Chroococcus+Cryptomonas; Ⅱ: Merismopedia+Synedra+Scenedesmus+Oocystis+Coelastrum; Ⅲ:Cyclotella+Navicula; VI:Chlamydomonas+Cyclotella+Synedra+Chlorococcum+Scenedesmus; V:Phormidium+Cymbella+Dactylococcopsis; Ⅵ:Cyclotella+Synedra+Chlorococcum+Scenedesmus;Ⅶ:Cyclotella+Chlorococcum+Cryptomonas; Ⅷ:Scenedesmus+Dactylococcopsis+Chlorococcum+Coelastrum.(5) Phytoplankton has divided into functional group of A、C、D、P、F、G、X2、M、 Y、X1、S1、T、TC、H1、SN、W1、W2、N、S2、X3、J. L0、MP. Functional groups of C、MP、X1、X2、W1、TC、Y、D、J、S1、L0、F、SN、N、H1、P were dominant functional groups. C+MP and W1were dominant of functional group in the three years of investigation. L0and J were dominant in spring and summer. TC was dominant in summer. H2was dominant in the autumn and winter. According to the quantity of functional groups, quantity of functional groups was center of lake> south of lake> estuary of Lake. Depth, temperature, pH and Chlorophyll were main driving factor of functional composition and seasonal succession.(6) Ecological modelling analysis shown TN,TP,NH4+andNO3-were the highest in winter and spring.The peak of green biomass was in spring,valley in the autumn,slight increase in winter. The change of diatom biomass fluctuated greatly in whole year.