Study On The Dynamics Of Phytoplankton In Sediment-Water Interface Of Jiulong River Xipi Reservoir

The community structure and the abundance of phytoplankton are closely related to eutrophication.To study the composition and abundance of phytoplankton in sediment-water interface in XiPi reservoir of Jiulong river,the methods of the field monitoring and laboratory simulation experiment were combined.Water samples of sediment-water interface/surface/middle layer/and surface sediment samples collected many times in 2015 were analyzed including the composition and abundance of algae.The results showed that the abundance of phytoplankton in sediment-water interface reach 105 cells/L?106 cells/L,the composition of phytoplankton were dominated with Chlorophyta,Cyanophyta and Cryptophyta,accounting for 15.22%?80.36%,16.07%?50.75%,1.79%?48.78%of algal abundance respectively;The succession of phytoplankton community from spring to winter in surface,with the increasing of temperature,the species of Cryptophyta and Chlorophyta that accounting for 16.20%?57.35%,30.42%?50.35%of algal abundance respectively in spring changes to the dominant of Chlorophyta,which accounting for 40.57%?82.53%of algal abundance,with the decreasing of temperature,the composition of the phytoplankton showed more diverse,dominated with Chlorophyta,Cyanophyta and Cryptophyta in the autumn;dominated with Bacillariophyta,Cryptophyta and Chlorophyta in winter;its abundance of phytoplankton can reach 105 cells/L?106 cells/L;The dominant microalgal species in the sediment belong to Bacillariophyta,accounting for 53.26%?83.53%of total microalgal abundance.In order to explore the factors afected the community composition and abundance of phytoplankton in vertical water,The methods of canonical correspondence analysis(CCA)and principal component analysis(PCA)were applied.It shows that the phytoplankton in the sediment-water interface were controlled with nutrients,especially dissolved organic nitrogen,soluble reactive phosphorus,dissolved organic phosphorusless;the phytoplankton in surface water were mainly influenced by external factors,temperature and nutrients' forms are important factors on the the community composition and abundance of phytoplankton in surface water.The succession of phytoplankton has been analyzed,the results show that the algae in sediment-water interface can be influenced by the upper of water body and sediments,mainly constitute of Chlorophyta,Bacillariophyta,Cyanophyta;the change of phytoplankton in intermediat layer is similar with the community of phytoplankton in surface water,algae community structure is relatively stable in June to October,mainly dominates with Chlorophyta,accounting for 28.86%?82.14%and 44.65%?68.66%of algal abundance in the surface and tntermediat layer respectively;microalgae in the sediment is relatively steady,small changes in community structure throughout the year.The responses of proliferation of sediment-water interface algae to phosphorus were analyzed by regulating different forms of phosphorus.The experimental results suggested that phytoplankton use of different forms of phosphorus in the presence of specific.Algae-based on Bacillariophyta/Chlorophyta/Cyanophyta,accounting for 49.16%,49.16%,17.32%of total algal abundance,transformed to the dominant of Cyanphyta and Chlorophyta,accounting for 17.32%?80.07%,19.85%?49.91%,when inorganic phosphorus(NaH2PO4·2H2O)as the sources of phosphorus.Organic phosphorus(AMP)as phosphorus source in the culture,Chlorophyta slowly become dominant species,highest occupying 92.51%of total algal abundanceThe perspectives of this study from the surface water extend to sediment-water interface to study the structure composition of phytoplankton.The results would contribute to a better understanding of the mechanism of bloom in cascade reservoir of Jiulong river.