The Study On Phytoplankton Community Structure In Lake Caizi

Caizi Lake is one of the most important lake of the wetland of the Changjiang River in Anhui Province, China.lt was not influencedl by human before,but in the last few years,as the development of aquaculture vigorously,It has been severely disturbed.The increasing of grazing fish and crabs leads to the significantly reduced of aquatic plants and obviously decreased of the vegetation coverage.In2000the vegetation coverage is80%,in2007is50%and in2009is3%.The study is based on the research of phytoplankton structure in recent years of Lake Caizi,comparing to the study of2006-2007,to explore the dynamic of phytoplankton community to the chang of vegetation coverage.The phytoplankton samplings were taken in January,march, may, July September and November in Lake Caizi.The dominant index (Y), Margalef abundance index(D), Shannon-Weaver diversity index (H’), Pielou index (J), Jaccard similarity index (X) and clustering analysis were used to analysis the phytoplankton diversity.The composition of phytoplankton species of2012was studied.Chlorophyta, Diatoms,Cyanophyta, Euglenophyta,Xanthophyta, Chrysophyta, Cryptophyta, dinoflagellates were identified.As for the Chlorophyta, Diatoms,Cyanophyta had the most species they are one of the reason of the phyplankton structure chang. The maximal number of phytoplankton species occurred in March while the minimum appeared in January.The phytoplankton dominant species was studied. Cyanophyta peaked all the year round:Oscillatoria subcontorta,Nostoc minutum,Anabaena variabilis,Merismopedia marssonii.planktolyngbya subtilis.Aphanizomeno flos-aquae; Diatoms had an apparent dominance in January,May, September and November: Melodira granulate, Synedra acus, Synedra ulna, Melodira granulata van angustissima;Xanthophyta also played an important role in January, March and May: ribonema minus,Tribonema affine; Chloroph.yta(Ankistrodesmus angustus) and Cryptophyta(Cryptomonas erosa) dominated in May while Chrysophyta dominated in January, Dinobryon bavaricum.The dynamics of cell density was higher in summer and autumn than that in winter and spring. The maximal density, with the value of (66.13±8.58)×105cells/L, occurred in July while the minimal, with the value of (12.78±0.61)×105cells/L appeared in January.Diatoms dominanted in winter, Xanthophyta dominanted in spring and Cyanophyta dominanted in summer and antumn.The dynamics of biomass was higher in autumn than other seasons, the maximal biomass of phytoplankton,occurred in September and the minimal, appeared in May.The results of Jaccard index (X) shew the obvious phytoplankton structure seasonal succession.It was between0.25-0.57,revealing the poor phytoplankton structure similarity and obvious habitat difference.lt maximum value is0.57between September and November and Minimum value is0.25between January and July.Temporal variations of three indices (including Margalef index, Shannon-Wiener index and Pielou evenness index) were obvious. All the indices were higher in winter and spring than that in summer and autumn. The maximal value occurred in March while the minimal one appeared in July.The phytoplankton community structure was influenced by different factors in different months. As a result, the groups of sampling station changed seasonally according to cluster analysis.The obvious variation of phytoplankton community structure was present in2010compared with that in2007. The number of species decreased from340in2007to285in2010, however, the cell density increased obviously from (5.91±0.90)×105cells/L in2007to (33.81±10.10)×105cells/L in2010. At the same time, both the number of oligotrophic algae and perphytic algae decreased to same extent and eutrophic, filamentous and planktonic algae increased.