Indicators Of Phytoplankton On Water Environment Of Plateau Reservoirs And The Study Of Nutrients Limitation Control Phytoplankton Growth

Both Hongfeng Reservoir and Baihua Reservoir belong to the upper and lower reaches of the Maotiao River,the tributary from Wujiang River Basin.They are important drinking water sources with many functions such as irrigation,power generation,flood control,and tourism.In recent years,with the intensification of human activities,the eutrophication of the two reservoirs has been aggravated and the water ecosystem has undergone major variation.In order to reveal the selection mechanism of the phytoplankton community with the changeable of habitats in Guizhou,this study conducted a monthly sampling survey of Hongfeng Reservoir and Baihua Reservoir from March 2016 to December 2017.Our aim is to elucidating the dynamic characteristics of phytoplankton community structure in the two reservoirs and forming a functional category oriented to the ecological attributes of the phytoplankton community.At the same time,in order to understand the regulatory mechanisms of changeable in nitrogen and phosphorus on the growth of phytoplankton in the Guizhou reservoir,situ experiments were conducted at Baihua Reservoir and Aha Reservoir in April,July,October,December 2017.The data analysis results showing that:There were 64 genus and 6 phyla phytoplankton has been identified in Hongfeng Reservoir,58 genus and 6 phyla phytoplankton has been identified in Baihua Reservoir.Diatoms had the largest numbers of species in two reservoirs which dominant species were Cyclotella sp.,follow by green algae.The phytoplankton community structure in the two reservoirs is dinoflagellate-diatom-green algae in spring and diatom-green algae-cyanophyta in summer,and is dominated by diatoms in autumn and winter.The slightly difference is Baihua Reservoir in spring which dinoflagellate biomass too high to form blooms.At the same time,due to the survival characteristics of algae,there are differences in the structure of phytoplankton from the surface layer to the bottom layer.The diatoms occupy a certain proportion in the surface,middle,and bottom layer of water.Cyanobacteria,dinoflagellates,and green algae mainly occur in the surface water of two reservoirs.Overall,the species richness and biomass of the middle and bottom layers are inferior to the surface layer,and the phytoplankton biomass:surface>middle>bottom.The species diversity of Hongfeng Reservoir is higher than that of Baihua Reservoir.The inherent stability of Hongfeng Reservoir is high,and the community structure is relatively stable and will not be easily to replace.However,with time going on,the species diversity of Hongfeng Reservoir is declining year by year.The two reservoirs were classified to compare the actual application status of different functional groups in Guizhou reservoirs.FG:The Hongfeng Reservoir collectively classified to 18 functional groups,and Baihua Reservoir classified to 15 functional groups.Hongfeng Reservoir is dominated by B/D/P/L_O,and the phytoplankton community structure is relatively stable.The Baihua Reservoir is mainly dominated by B/D/L_O.During the period,Dinoflagellates bloomed.MFG:Hongfeng Reservoir is dominated by 1b/6a/6b/7a/7b/11c,while Baihua Reservoir is dominated by 1b/1c/6b/7a/7b.The composition of the dominant functional groups of Hongfeng Reservoir in 2016 and 2017 is relatively consistent,and the relative biomass accounts for a slight change.The succession of phytoplankton community structure in Baihua Reservoir is more frequent than Hongfeng Reservoir.MBFG:Hongfeng Reservoir and Baihua Reservoir are both mostly composed of functional groups IV,V and VI.Comparing the seasonal succession of FG,MFG and MBFG functional groups in the two reservoirs,it is found that these three classification methods can reflect the replacement of the phytoplankton community structure of the two reservoirs effectivity.However,the discrimination of MBFG is not particularly obvious compare with other functional groups which FG and MFG performed more clearly.After RDA analysis of the impact of environmental factors of two reservoirs on the distribution of phytoplankton functional groups,water temperature can significantly affect the distribution of three functional groups,while nutrients are not the main environmental factors.The analysis of FG and MFG showed that the main environmental factors explained the species distribution more than MBFG.According to the general limit standard,Baihua Reservoir and Aha Reservoir all show the characteristics of phosphorus limitation.The nutrients enrichment experiment results showed that the addition of nitrogen in the summer and autumn seasons of the Baihua Reservoir had a greater promoting effect on the growth of algae.Instead,the algae had not obviously response to the addition of phosphorus,indicating nitrogen limitation characteristics.Aha Reservoir showed the characteristics of limits both nitrogen and phosphorus.The experiment of nitrogen and phosphorus limitation in Aha Reservoir showed that the growth rate of phytoplankton was the highest in summer and lowest in winter.Compared with the growth rates of different algae,cyanobacteria and dinoflagellates have higher growth rates,and are easier to gain advantage in the early stages of succession.Diatoms and green algae have lower growth rates and are good at storing nutrients which can provide energy in later growth period.At the beginning of the experiment,cyanobacteria and dinoflagellates occupy a certain dominant position,and the green algae gain competitive advantage in the later period.During the simulation experiment,the phytoplankton utilization rate of NO₃-N was higher,summer was the highest,and autumn and winter were low.In the P-invariant experimental group,the absorption and utilization of inorganic nitrogen and the conversion rate were low.