The Spatio-temporal Pattern Of Phytoplankton In Lake Fuxian

Lake Fuxian,one of the most important drinking water source of YunnanProvince,has been received widespread attention.In order to study the spatial and temporal variation of phytoplankton community structure in Lake Fuxian and their realationship with environmental factors,phytoplankton species composition and water environmental factors were collected from 15 sampling selected sites were all round the lake once a month from July to December 2014.Also,in July 2014,we selected three sample points in central,southern and northernof the lake to study phytoplanktonvertical distrubtion pattern.The main results are as follow:(1)During the investigation,a total of 7 Phylums,44genera,65 species of phytoplankton were collected.The phytoplankton community of was mainly composed of Chlorophyta(22genera,34species),Bacillariophyta(11genera,16species),Cyanophyta(6genera,6 species),Cryptophyt(2genera,4species),Pyrrophyta(2genera,2species),Chrysophyta(lgenera,1speicies)Mougeotia.sp,Oocystis elliptica,Cearium hirundinella andDinobryon divergens were dominant species in Lake Fuxian.(2)During the investigation,the mean phytoplankton biomass was about 0.3mg/L,the maximum occured in August and the mean biomass is 0.7mg/L.From September to December,phytoplankton biomass decline continuously and the mean biomass in December wass O.lmg/L.On the vertical distribution of phytoplankton is mainly distributed in 0-20 m layer,the average biomass is 0.67mg/L and the phytoplankton biomass is decliningbelow 20m waters.The horizontal distribution of phytoplankton biomass from high to low was north,south and center.(3)Results showed that the number of phytoplankton of Fuxian Lake has increasedin the recent years.In 2014,the phytoplankton density is 1.22×106cells/L and it is 9.5 times that of 1980.Compared with 1980,biomass of Chlorophyta and Cyanophyta increased by 14.6 times and 7.3 times respectively.The dominant species changed drasticly,from 2005 MougeotiaSp.began to become dominant species in Fuxian Lake and became dominant species in each month.On the contrary,the number of Aphanizomenon flos-aquae began to decreasein Lake Fuxian from 1996 and it was not the dominant species in this survey.(4)Correlation analysis showed that temperature,pH,dissolved oxyge and conductivity were the main factor which affected phytoplankton biomass.The water depth,pH,temperature,dissolved oxygen and conductivity were the main factors which affected the distribution of phytoplankton above the thermocline layer,and the dissolved oxygen and pH were the main factorsthat affectedphytoplankton biomass in vertical directions.(5)Redundancy analysis showed that the main factors affectingDinobryon divergens temporal pattern were the conductivity and total nitrogen,and them vertical changeswere affected by the dissolved oxygen and total phosphorus.Clarity and dissolved oxygen influenced Mougeotia sp.temporal pattern and total nitrogen,temperature,conductivity and depth affected its vertical patern.For Tetaerdorn trilboulatum permanganate index significantly influenced its time pattern and total nitrogen,temperature and conductivity significantly influenced its verticalpattern.Clarity,dissolved oxygen and dissolved oxygen were the main factors which affected Oocystis elliptica time changes and pH was main factors which affected Oocystis elliptica space distribution.From Cearium hirundinella,the main factors which affected spatiotemporal variation were temperature and pH,and the dissolved oxygen andtotal phosphorus,respectively.Also,there were storng correlation between variation of biomass Aphanocapsa elachistaandpermanganate index.