Responses Of Phytoplankton To Water Level Changes And Human Disturbance In Poyang Lake

Poyang Lake which is located in the northern part of Jiangxi Province is the largest freshwater lake in China.The lake is significantly affected by climate change and human disturbance.This study selected 15 sampling points and one deposition column sampling point in Poyang Lake January,April,April,July and October in 2015-2017?representing winter,spring,summer and Fall respectively?.A sampling survey was conducted and samples of sedimentary columns were collected in July 2017.By using principal component analysis to analyze seasonal characteristics and point characteristics of water quality in Poyang Lake in the past three years,seasonal and spatial analysis of phytoplankton biomass,abundance,and dominant species were conducted,and Pearson correlation was discussed using SPSS 19.0.The physicochemical parameters of phytoplankton community and water were analyzed,and the sedimentary diatom assemblage was analyzed using the upper sample?0-21 g·cm-2?representing the deposition in the past 60 years to reflect the climate change in Poyang Lake over the past 60 years.Concluded as follow:1)Through principal component analysis,the eigenvector load diagram shows the highest contribution rates of SS,T,WT,pH,SD and TP,and PO^4--P,followed by COD,NO^2--N,NH⁴⁺-N,TN/TP,and TN.And Chl-a,finally NO^3--N and DO.The main influencing factors affecting seasonal water quality of Poyang Lake were suspended particles SS,water temperature T,water level WT,pH,and transparency SD.The main pollutants were TP.The comprehensive scores indicated that the water quality of Poyang Lake was the best in summer,followed by spring and winter.Fall is the worst.Poyang Lake has fast flow velocity and high turbidity during low water level.Its characteristics include low water temperature,high nutrient concentration,high TN/TP ratio,low Chl-a content,high water level,slow water velocity,high transparency,and water characteristics.The water temperature is high,the nutrient concentration is relatively low,the TN/TP ratio is low,and the Chl-a content is high.2)Using PCA to analyze Poyang Lake water point differences,it can be seen that the water quality of Poyang Lake's water body except the western side of the shoe and the Le'an estuary is Class IV.The water quality of the estuary is higher than that of the lake.Since the biological sewage flows into the Poyang Lake from the estuary,the estuaries have more pollutants and higher nutrient content.3)Seasonal changes in total abundance and total biomass of phytoplankton are expressed as:summer>autumn>winter>spring;abundance of blue-green algae predominates in abundance statistics,and from biomass statistics,diatoms Biomass dominates.The linear linear diatoms and the cryptophytes of soft cryptic algae are perennial dominant species and are distributed in every season.The narrow-chain algae species,Cryptocarya cryptosporium,and Crytophyta are the subdominant species.Others such as dinoflagellates and anchovy Appears only in individual seasons.The linear diatoms predominate in the summer,while the cryptophytes of the ovum predominate in the fall.The abundance and biomass of phytoplankton and biomass of each algal phytoplankton are significantly related to Chl-a,SD,T and pH.Diatoms are extremely sensitive to changes in the water environment,and the nutrient concentration,salinity,depth,flow rate,Physicochemical properties such as temperature will cause changes in diatom species and their content.4)In this study,diatoms were better preserved in sediments.A total of 128 species?including varieties and variants?of diatoms belonging to 15 genera,9 families in 2 orders and 5 orders were identified in 31 samples of deposit PYH135#1 sediments.The distribution statistics of fossil diatoms in the order of heads,families,genus and species indicated that Naviculales species are the most common,with 58 species,followed by 34 species of Aulonaphidinales,25 species of Biraphidinales,and 18 species of Nitzschi species.In all families,the Naviculacea family has the largest number of species,38 species;followed by the Cymbellaceae family of 20 species,the Biraphidinales family of 17 Gomphonemaceae families of 8 species;they accounted for 29.6%,15.6%,13.3%,and 6.3%of the total.Among all genera,Navicula species are the most common,with 38 species,followed by 20 species of Cymbella,18 species of Nitzschia,11 species of Eunotia,and 8 species of Gomphonema.They account for 29.6%,15.6%,and 14.1%of the total respectively.8.5%,6.3%.The number of species of the above major diatoms accounted for 74.1%of the total,of which Bacillariophyceae class 4 orders 8 families 12 genera and 122 species,accounting for 95.53%of the total species.Therefore,the sedimentary diatoms in this study are basically shell-seam diatoms.After 2010,A.granulata was replaced with nutrient-tolerant planktonic diatom A.ambigua and there were known eutrophication indicators in surface samples,such as low-frequency A.alpigena,C.meneghiniana,and C.pseudostelligera,indicating that Poyang Lake may have Transferred to an unprecedented nutrient-rich state.Over the past 60 years,Lake Poyang has changed from a nutrient-poor state that is naturally hydrologically connected to a limited hydrology-related eutrophic state.