The Characteristics Of Community Structure Of Planktonic Algae And Water Quality Assessment In Dishui Lake, Shanghai

Dishui Lake is a newly-built lake on a beach, so far it is the largest artificiallandscape lake in China, which has a wealth of wetland resources. The lake is round,and the total area of the lake is5.56km2with the diameter of2.66km2. Dishui Lake is afreshwater lake, however, the pH value of lake water showed alkaline. As the lake builton a beach, its salinity usually higher than other inland freshwater lakes, that is withgreat significance in ecological environment. Meanwhile, as a newly-built lake, itsbenign ecosystem has not found yet, and the ecological environment is still unstable.The water quality of Dishui Lake played an important role in Shanghai Harbor City’sfuture urban development, as this can indirectly reflects the safety status of waterquality of the environment in Shanghai, so the sustainable investigation research onwater quality is particularly important. A preliminary study was conducted on theplanktonic algae community characteristics once a month from March2009to February2011in Dishui Lake at8sample stations. Statistical Program for Social Sciences （SPSS）was used for correlation analysis between physicochemical parameters and algaestanding crop. Canonical correspondence analysis （CCA） was applied to further explorethe correlation between algae species and environmental factors using CANOCO4.5.The aim of this study was designed to reveal the dynamic variation of the planktonicalgae community structure responded to ecological environment. Furthermore, it is alsohoped that this study will provide further insights into sustainable research on otherartificial lakes in the future, such as water quality management, sustainable exploitationand conservation on landscape water resources.The main results as below:1. A total of230species and varieties of planktonic algae were found in DishuiLake, which belonged to105genera of8phyla. Chlorophyta were the most importantcomponent, the quantity was111species belonged to43genera, which accounted for 48.26percent. Second in abundance was Cyanophyta amounted16.09percent, thequantity was37species belonged to20genera. Then come to Bacillariophyta, with apercentage of15.65. The others belonged to Euglenophyta, Xanthophyta, Pyrrophyta,Chrysophyta and Cryptophyta. The species numbers of planktonic algae were higher insummer and autumn, lowest in winter.2. The average annual density and biomass of planktonic algae were（3680.09±3446.78）×10⁴cells·L^-1and （7.63±5.18） mg·L^-1, respectively. Two of them allhad seasonal variation, but not in the same trend. Meanwhile, both of them had thedecreasing trend on the whole.3. There were32dominant species of planktonic algae from March2009toFebruary2010in Dishui Lake, and22species from March2010to February2011. Thetop4of the species’ dominance were all included Merismopedia tenuissima,Phorimidium tenus and Microcystis incerta. The composition of dominant species bothhad significant seasonal variation in the two year, the number of dominant specieshigher in spring, lower in winter. Bacillariophyta and Cryptophyta were dominant inwinter and spring, and Cyanophyta were absolutely dominant in summer.4. The density and biomass of planktonic algae both had significant positivecorrelation with water temperature and Chl-a, but significant negative correlation withtransparency. The density also had significant positive correlation with CODMn, andsignificant correlation with pH and PO4-P. The biomass had significant positivecorrelation with pH, PO4-P and TN, and significant correlation with TP. As shown inCCA during the two year, we can see that the main factors affecting communitystructure of planktonic algae were water temperature, total nitrogen and transparency inthe year of2009²010, but water temperature, pH and transparency in the year of2010²011. In summary, water temperature was the most important environmentalfactor that affected the community structure of planktonic algae in Dishui Lake.5. The average value of H’, D, J and Dv of planktonic algae were （2.51±0.59）,（3.06±0.45）,（0.63±0.15） and （1.68±0.67）, respectively. All of these diversity indexeshad remarkable seasonal variation, the seasonal variation of H’, J and Dv had the similartrend, they were all higher in winter and spring, lower in summer and autumn, on thecontrary, the seasonal variation of D higher in summer and autumn, lower in winter andspring.6. The average value of TSIMand TLI were （63.77±3.85） and （60.37±5.68）, respectively. They had the same trend of seasonal variation, both of them were higher insummer and autumn, and lower in winter and spring.7. Based on criteria for evaluating trophic status, it can be concluded that DishuiLake were both at α-β-mesoeutrophy level during the year of2009²010and2010²011. However, eutrophication weakened year by year, water quality wasgradually getting better.