Dynamic And Influencing Factors Of Phytoplankton Community Structure In North Creek Of Jiulong River

As a primary producer of rivers,phytoplankton plays an important role in maintaining the cyclical transformation of matter and energy in river ecosystems.Its community structure can directly or indirectly reflect the health status of water bodies.Therefore,studying the community structure of phytoplankton and its succession has important ecological significance of river ecosystems,especially with the increase of eutrophication of water bodies,algae outbreaks have become a major hidden danger affecting the ecological health and safety of the river.In order to study the relationship between phytoplankton community structure and environmental factors in North Creek,Jiulong River,Fujian.The study conducted research on the seasonal variation,diversity and environmental factors of phytoplankton community in North Creek,Jiulong River in the period from April 2018 to January 2019 and obtained the following main results:1.Distribution of phytoplankton in North Creek,Jiulong RiverUsing the microscope to identify the species of North Creek,Jiulong River from April 2018 to January 2019 every month.The monthly sampling show that there were 132 species of 82 genera,7 phylums of phytoplankton.The species of Chlorophyta was the most diverse and 59 species of 34 genera were found.Followed by Bacillariophyta,36 species of 19 genera were found There are also 15 genera 16 species of Cyanophyta,4 genera 8 species of Euglenophyta,4 genera 5 species of Pyrrotata,2 genera 4 species of Cryptophyta and 4 genera 4 species of Chrysophyta.The abundance of phytoplankton cells in Jiulong River is characterized by spring>summer>winter>autumn,and the succession of the phytoplankton of North Creek Jiulong River is Bacillariophyta-Chlorophyta(spring)—Cyanophyta(summer)—Bacillariophyta-Chlorophyta(autumn)—Bacillariophyta-Cryptophyta(winter).2.Phytoplankton diversity in North Creek,Jiulong RiverThe phytoplankton sampled every month is seasonally differentiated.The order of average of Shannon-Wiener diversity index is spring(1.79)>summer(1.76)>winter(1-57)>autumn(1.56),the order of average of Margelaf richness index is summer(2.42)>sprnng(2.34)>winter(2.14)>autumn(2.11)and the order of averages of Pielou evenness index is spring(0.74)=autumn(0.74)>summer(0.72)>winter(0.71).The phytoplankton Shannon-Wiener diversity index and Margelaf richness index did not differ significantly in spring and summer and were also no significant difference in autumn and winter.It is related to the similar phytoplankton community structure and similar algal density in spring and summer,also in autumn and winter.However,the change of the Pielou evenness index is not large,to a certain extent,it shows that the community composition of the entire river in North Creek,Jiulong River is relatively stable,the succession is relatively stable,the quantity distribution is relatively uniform,and there is no abnormal algae outbreak.3.Impact factors of phytoplankton community structure in North Creek,Jiulong RiverThe main environmental factors affecting the distribution of phytoplankton community in the North Creek are the chlorophyll-a,temperature,total phosphorus and pH.The influence factors are different in different seasons.The main influencing factors in spring are chlorophyll-a and total phosphorus.The main factors in summer are chlorophyll-a and CODMn.The main factors in autumn are chlorophyll-a and total nitrogen,iron and pH.The main factors in winter are chlorophyll-a and nitrite.4.Preliminary study on high-throughput sequencing techniques in North Creek,Jiulong RiverThis study initially explored the application of high-throughput sequencing technology in the identification of eukaryotic phytoplankton in North Creek.Comparing the results of high-throughput sequencing and microscopic observation,from the perspective of species dominant species,both methods show that the dominant communities of the eukaryotic algae in the Jiulong River are the Chlorophyta and Bacillariophyta.In the high-throughput sequencing,a total of 164 species 107 genera 6 phylums of eukaryotic planktonic algae were detected,which was more abundant than the results of 63 species 32 genera 6 phylums of microscopic examination in May.That indicated that high-throughput sequencing could detect species that could not be observed in optical microscopy.However,microscopic examination revealed the presence of Euglenophyta and was not found in high-throughput sequencing results.It may be due to the lack of gene infomnation in the selected V4 variable region or V4 variable region primer that does not contain the gene.A database of phytoplankton DNA barcodes in local freshwater ecosystems is necessary.In addition,high-throughput sequencing technology found 186 species 125 genera 5 phylums of eukaryotic phytoplankton in the sediment,the dominant species are also the Chlorophyta and Bacillariophyta,which is rich in species,but the dominant species are not obvious and the distribution is relatively uniform,but the content of Pyrrotata in the sediment is more than water,the sediment possibly contains Pyrrotata cysts.