Study On The Spatiotemporal Variation And Correlation Of Factors And Phytoplankton Community Structure And Water Environmental Factors In Ertan Reservoir

Ertan Reservoir belongs to the lower reaches of the Yalong River,a primary tributary of the Yangtze River.It is an important part of the ecological barrier area in the upstream of the Yangtze River and has multiple functions to serve human society.Phytoplankton is an important part of the aquatic ecological environmental investigation.The dynamic changes of phytoplankton community composition are closely related to water environmental factors.Monitoring the phytoplankton and water quality status of reservoirs plays an important role in ensuring the normal operation of reservoir.Proving the internal relationship between phytoplankton and water environmental factors can provide theoretical reference for formulating reasonable reservoir management.Based on this,this study conducted an annual four-season survey of phytoplankton and water environmental factors in Ertan Reservoir from December 2018 to October 2019.This study analyzed the status of water quality and phytoplankton community structure of each sampling section of the reservoir in different seasons,the correlation between phytoplankton with water environment factors and the difference with this survey and historical survey.The results of the study are as follows:1.Water environmental factors and water qualityThe water quality of Ertan Reservoir was in Class II-III throughout the year.WT,p H,DO,EC,HG,TN,NO₂^--N,TP,COD_Mnand Chl a in 5 sampling sections throughout the year varied between 13.8 and 31.0?,between 8.3 and 9.3,between13.8 and 31.0 mg/L,between 161.4 and 309.0us/cm,between 1.59 and 6.03 mmol/L,between 0.149 and 1.182 mg/L,between 0.003 and 0.035 mg/L,between 0.006 and0.176 mg/L,between 1.45 and 7.28 mg/L,between 0.212 and 7.383 ug/L,respectively.Seasonal differences in water environmental factors of Ertan Reservoir were significant.The annual overall WT in summer was significantly higher than other seasons.p H,TP,NO₂^--N and Chl a in autumn were significantly higher than other seasons;EC and TN in winter were significantly lower than other seasons;HG in winter and spring were significantly higher than summer and autumn;COD_Mnpresented the tend of:autumn>summer>spring.The water environmental factors of Ertan Reservoir also had spatial differences.WT and p H of the tributary section were significantly higher than those of the mainstream section in general;DO of the tributary section was significantly higher than that of the mainstream section in summer and autumn;the content of nitrogen and phosphorus in the tributary section were also at a higher level,HG was not significantly different in all sections.In terms of whole water environmental factors,Ertan Reservoir was in an oligotrophic state closing to mesotrophic state.The degree of eutrophication in the season was autumn>summer>winter>spring,and on spece showed ET-3>ET-4>ET-1>ET-2>ET-5,the tributaries are higher than the main stream,and the tail of the reservoir was larger than the front of the dam.2.Phytoplankton community structure statusA total of 124 species of phytoplankton in 8 phyla were found throughout the year,49 species were detected in the Chlorophyta,43 species in the Diatom phyta;13species in the Cyanophyta;10 species in Euglena.The number of algae specie of Dinophyta,Xanthophyta,Chrysophyta and Cryptophyta were relatively small.The number of phytoplankton species presented winter>summer>spring>autumn in season..The annual variation range of phytoplankton density and biomass varied between 0.205×10⁶ and 3.502×10⁶ ind./L,between 0.20 and 1.62 mg/L,respectively.The average value of density and biomass showed ET-3>ET-5>ET-4?ET-1>ET-2.The dominant species of phytoplankton were mainly Chlorophyta and Diatoms.The succession was not obvious between different sections,but more obvious between different seasons.The Shannon-Wiener diversity index varied from 2.21 to 3.96,which was significantly higher in summer than in other seasons,and lower in winter and spring;ET-3,ET-5 and ET-1 were higher than other sections.The Pielous evenness index varied from 0.70 to 0.93,which was similar in spring,summer and winter,and lower in autumn.It showed ET-1>ET-2>ET-3?ET-5>ET-4 in sections.Based on these two diversity indexes to evaluating the water quality,the water body of Ertan Reservoir was in a non-polluted or lightly polluted state.3.The relationship between phytoplankton community and physicochemical properties of waterThe physical and chemical properties of water are important factors affecting the changes in the phytoplankton community structure.Pearson correlation analysis showed that TN had a significant positive correlation with phytoplankton density,COD_Mn had a significant positive correlation with phytoplankton density,and WT had a significant positive correlation with Shannon-Wiener diversity index.The results of redundancy analysis results showed that p H and TN were significantly related to the phytoplankton community structure parameters.The results of canonical correspondence analysis showed that HG,WT,p H and EC were the main factors affecting the abundance of phytoplankton dominant species.4.Comparative study of differences with historical dataCompared with the historical data of 2016?2017,the eutrophication status showed the same change in seasons.The eutrophication status increased from spring to autumn,and decreased in winter.Compared with the historical data of 2010?2014,TN,TP and COD_Mn were all significantly reduced,and water quality improved.The composition of the phytoplankton community was highly consistent with historical date,and they were both the green algae-diatom type;the number of phytoplankton species in whole year was lower than the historical data.The variation range of phytoplankton diversity index was similar,and the correlation with water environment factors was consistent.