| Grasping the basic characteristics of phytoplankton population structure and its temporal and spatial changes as well as its response to environmental factors will help to understand the process and mechanism of water eutrophication,which can help improve water quality,prevent the occurrence of cyanobacteria blooms,and manage water resources in reservoirs.Used to provide an important reference.In this study,from June 2018 to November 2019,five sampling points were set up in Shankouyan Reservoir in Pingxiang City,Jiangxi Province.The community structure characteristics of phytoplankton were investigated month by month,and the corresponding environmental factors were monitored,and related Sexual analysis and redundancy analysis methods discussed the impact of environmental factors on the structure of phytoplankton community.The main conclusions are as follows:1.During the investigation,a total of 64 species of phytoplankton,46 genera and7 phyla were detected.The Chlorophyta species accounted for the largest proportion of 39.06%,followed by the Diatom phyla with 32.81%,Cyanophyta with 18.75%,and the remaining Cryptophyta and Euglena,Dinophyta and Chrysophyta together accounted for 9.38%.The seasonal variation of the number of phytoplankton species was more in summer and autumn,and less in winter and spring;the horizontal change was not obvious;the number of phytoplankton species gradually decreases from the surface to the bottom.The variation range of phytoplankton abundance was(5.96×10~6～100.38×10~6)cells/L,and the annual average abundance was 29.03×10~6cells/L.The highest abundance of Cyanophyta was 65.08%,Chlorophyta was16.28%,Diatoms was 13.8%,Cryptophyta was 4.72%,and the remaining three categories only account for 0.13%.The seasonal variation of phytoplankton abundance was higher in summer and autumn than in winter and spring;the horizontal variation was characterized by the highest abundance in the upper reaches of the reservoir,followed by the downstream,and the lowest in the middle reaches;the phytoplankton abundance gradually decreases from the surface to the bottom in the vertical direction.2.During the study period,there were 4 phylums and 20 species with obvious advantages,10 species of Cyanophyta,5 species of Diatoms,4 species of Chlorophyta,and 1 species of Cryptophyta.The types and dominance of dominant species show obvious seasonal changes,which were more in summer and autumn and less in winter and spring;the succession pattern of phytoplankton community structure is:Summer of 2018:cyanobacteria-green algae;Autumn:green algae-cryptophyta-cyanobacteria;Winter:Diatom-Cyanobacteria-Cryptomonas;Spring of 2019:Diatom-Cyanobacteria;Summer:Cyanobacteria-Green Algae;Autumn:Cyanobacteria-Diatom.3.The phytoplankton Shanno diversity index H’and Pielou evenness index J are used to evaluate the water quality of the reservoir.The results showed that the index H’and the index J have basically the same changing trends,and the water quality of Shankouyan Reservoir was at a moderate pollution level.Compared with 2018,the water quality of 2019 had improved in the year.4.The annual change range of reservoir water temperature was 9.4～31.7°C;the annual change range of dissolved oxygen was 6.54～10.92mg/L;the annual change range of p H value was 5.52～9.57;the annual change range of transparency was1.22～3.5m;the annual variation range of total nitrogen was 0.09～1.28mg/L,and the annual average value was 0.71mg/L,which was in Class III standard water body as a whole;the annual variation range of ammonia nitrogen was 0.02～0.37mg/L,The annual average value was 0.14mg/L,and the whole was in Class I standard water body;the annual variation range of total phosphorus was 0.02～0.39mg/L,and the annual average value was 0.12mg/L,and the whole was in Class V standard water body.5.Correlation analysis showed that the number of phytoplankton species,the number of cyanophyta,and the number of green algae were significantly negatively correlated with dissolved oxygen,and the number of cyanobacteria was significantly positively correlated with water temperature;phytoplankton abundance was significantly positively correlated with p H;cyanobacteria The abundance of Phylum and Chlorophyta was significantly positively correlated with water temperature and p H;the abundance of Diatom Phylum was significantly negatively correlated with water temperature;Cryptophyta abundance was significantly negatively correlated with dissolved oxygen,and was extremely significantly positively correlated with total phosphorus;transparency;,Total nitrogen,total phosphorus,ammonia nitrogen,total iron and total manganese have little correlation with the number and density of phytoplankton.Redundant analysis showed that the dominant species of Microcystis and Chroococcus were positively correlated with water temperature and p H,Granular Melosira and Nitzschia were negatively correlated with water temperature,Fuzzy Melosira and Cryptomonas were positively correlated with transparency,and temperature had a positive correlation with planktonic algae.Interannual changes in abundance contribute the most and were an important environmental factor that affects the changes of phytoplankton communities.The analysis results of phytoplankton density composition and environmental factors showed that the main environmental factors that affect the phytoplankton density composition were different at different sampling points.On the whole,water temperature,dissolved oxygen,and p H contribute more to the density changed of green algae and cyanobacteria,and the greater impact on diatoms and cryptophytes was water temperature and total nitrogen. |
