Effects Of Water Level Fluctuations On Phytoplankton In Huayang River Lake Group

The Huayanghe lake Group is a natural lake connected with the Yangtze River,and its water situation is unique and distinct from that of the non connected the Yangtze River.In July 2016,extreme water level fluctuation occurred.In order to study the impact of water level fluctuation on water environment of Huayang River Lake Group and the response characteristics of phytoplankton,defending and managing biodiversity in natural protection area is crucial.Based on the four seasons investigation of Huayang River group,In this text,We get the principal study results as belows.1.In Huayanghe lake Group during the investigation,138 species are identified,belonging to 67 genera of 8 phylum,including 24 genera and 58 species of Chlorophyta,18 genera and 40 species of Bacillariophyta,12 genera and 21 species of Cyanophyta;5 genera and 10 species of Euglenophyta;3 genera and 3 species of Dinophyta;2 genera and 2 genera of Cryptophyta;1 genera and 1 species of Xanthophyta;1 species and 1 genus of Chrysophyt.The species number of phytoplankton species fluctuated obviously among the points.The species number of phytoplankton species fluctuated significantly among the points,reaching the maximum of 127 species at s13 in Huangda Lake and the lowest at S23 site in Po Lake,with 52 species.All sampling points are mainly Chlorophyta,followed by Bacillariophyta.There are 12 dominant species of phytoplankton in the Huayang he-lake group are Bacillariophyta,cyanobacteria and chlorophyta.2.Huayanghe lake Group average cell density ias 91.83×105 cells/L,range from 5.08 × 105 to 2.43 × 107 cells/L,when in winter,the cells density reached the highest,when in winter,the cells density is at the lowest level,cell density of Cyanophyta is highest,the proportion reached 78.36%,the phytoplankton cell density has obvious spatial differences,the overall performance of the trend is:Longgan Lake is the highest,the average cell density of 7.25 × 106 cells/L,followed by the Po Lake,the average cell density of 6.65 ×106 cells/L,Huangda Lake is the lowest,average cell density of 5.94 × 106 cells/L.The average biomass of Huayanghe lake Group is 7.13 mg/L,the range is 2.60?14.16 mg/L,the biomass in autumn is the highest,while in winter,phytoplankton biomass reaches its lowest level.Research in four seasons showed that,it is found that the biomass of Cyanophyta reached the maximum in summer.The diatoms biomass reached the highest value in spring and winter.There were obvious regional differences in biomass of phytoplankton,and the overall trend is as follows:Longgan Lake>Huangda Lake>Po Lake.The average biomass of phytoplankton in Longgan Lake is the largest,which is 8.98 mg/L.The average biomass of phytoplankton is 6.25 mg/L in the Huangda Lake and 6.15 mg/L in the Po Lake.3.The variation range of phytoplankton evenness index(J)in Huayanghe lake Group is 0.32?0.71,the average value is 0.55.Shannon-Winener index(H')is between 1.71?3.23(mean value is 2.49),the seasonal variation of richness index(D)is not obvious,the range of variation is 2.55?2.90,the average value is 2.77;in the case of spacial,the diversity index of phytoplankton in Huayanghe lake Group is obviously different in space,and the Shannong-Weiner diversity index(H')is the highest(2.68)in the Huangda Lake,followed by the Longgan Lake,which is 2.64;the Shannong-Weiner diversity index(H')is the lowest(2.18)in the Po Lake.The index of evenness(J)is:Huangda Lake is the highest,which is 0.61,the next is Po Lake,which is 0.57;The Longgan Lake is the lowest,which is 0.55,The index of richness(D)is the highest,which is 2.98;the second is Longgan Lake,which is 2.79,and the Huangda Lake is the lowest,which is 2.64.4.Redundancy analysis results show that the dominant species of phytoplankton were closely related to the environmental factors such as water temperature,dissolved oxygen,transparency,total nitrogen and chlorophyll a.Aulacoseira granulata var.There are positive correlation between angustissima and the temperature of the water,water level and pH;Lyngbya limnetica and Phormidium tenu is positively correlated with total phosphorus,turbidity,and exist negative correlation with dissolved oxygen,transparency and total nitrogen;positive correlation between Synedra acus,Aulacoseira granulata var.angustissima f.spiralis,Lyngbya limnetic,Aphanizomenon flosaquae,and Oscillatoria tenuis with chlorophyll a,but negatively correlated with water temperature,water depth and pH.Anabaena azotica and Merismopedia minima is positively correlated with transparency,conductivity,total nitrogen and dissolved oxygen,and there exist a negative correlation with turbidity.5.Extreme water level fluctuations water level fluctuationed lakes and connected rivers.The mean values of environmental factors,such as water level,pH and total nitrogen were the highest in summer.The structure of phytoplankton community changed obviously during the water level fluctuation period,after the rapid change of water level caused by heavy rainfall in July.The number of species reached the maximum of 109 species in the summer.The dominant species convert from spring Melosira to summer Mougeotia.In autumn,the dominant species are diatoms and cyanobacteria,mainly diatoms.The dominant group in winter is only diatoms.Extreme water level fluctuations can regulate phytoplankton community structure(including species composition,dominant species,etc.),seasonal succession and nutrient status of lakes.In the period of high water level,the number of phytoplankton species,the biomass and cell density reached the maximum.Therefore,the water level fluctuation could drive the water of Huayang River and Lake group to increase in light intensity and nutrition concentration,thus leading to a significant increase in biomass and species number of phytoplankton.