| Sampling was carried out in 2014 and 2015 in order to carry out the ecological environment present situation investigation in Yuqiao Reservoir.The phytoplankton samples and water samples were collected.We analyzed phytoplankton community structure characteristics and environmental factor such as the determination of nutrient,water temperature,dissolved oxygen and water transparency et al.Therefore,we can explore the main water environmental factors affecting the change of phytoplankton community for further research based on redundancy analysis(RDA).Besides,it was helpful for the preliminary analysis on reservoir eutrophication status.Combined with historical data,we can predict the trend of eutrophication in Yuqiao Reservoir.The main results were as follows:(1)A total of 113 species belonging to six phyla were identified in 2014 with 69 species belonging to Chlorophyta,24 species belonging to Diatoms,nine species belonging to Cyanophyta,five species belonging to Euglenophyta,two species belonging to Pyrrophyta and two belonging to Cryptophyta.In autumn,phytoplankton density was much lower than in summer and higher than in spring.The first dominant specie was Scenedesmus quadricauda in spring,whereas Microcystis aeruginos dominated in summer and Coelosphaerium kuetzingianum autumn.The seasonal variation of richness index d was autumn>spring>summer,while the seasonal variation of index J and Shannon-Weaver index H’ were both spring>autumn>summer.(2)A total of 70 species belonging to five phyla were identified in 2015 with 43 species belonging to Chlorophyta,14 species belonging to Diatoms,nine species belonging to Cyanophyta,two species belonging to Pyrrophyta and two belonging to Cryptophyta.In autumn,phytoplankton density was much lower than in summer and higher than in spring.The first dominant specie was Spirulinasp.in spring,whereas Microcystis aeruginos dominated in summer and autumn.The seasonal variation of richness index d was spring>summer>autumn,while the seasonal variation of index J and Shannon-Weaver index H’were both spring>autumn>summer.Compared with 2014,number of phytoplankton specie was reduced and the cells density and the value of dominant specie was increased.It was mainly due to the mounting eutrophication phenomenon in Yuqiao Reservoir,which leaded to the simpleness and instability of phytoplankton community structure and the decreasing of diversity function.(3)Based on RDA analysis,environment factors influenced on phytoplankton were familiar in 2014 and 2015.In spring,the species of phytoplankton were mainly belong to Chlorophyta in Yuqiao Reservoir.High concentration of nitrogen,high concentration of dissolved oxygen and low temperature was beneficial to the growth of Chlorophyta.It suggested that transparency,water temperature,the concentration of dissolved oxygen and nitrogen effected on the phytoplankton community composition of Yuqiao Reservoir during spring.In summer,as temperature rising,Cyanobacteria and Chlorophyta bloomed.Phytoplankton growth needed more nitrogen and phosphorus,which caused a decreasing of nitrogen and phosphorus concentration.The results indicated that the concentration of nitrogen,phosphorus and water temperature were the key environmental factors affecting on phytoplankton community composition.The quantity of Diatom increased again during autumn.It turned out that temperature and concentration of phosphorus were the main control factors in autumn.(4)In the spring of 2014,the nutrition state of Yuqiao Reservoir is mesotrophic,while it is moderate eutrophication in summer and eutrophication in autumn.In 2015,the nutrition state of Yuqiao Reservoir is moderate eutrophication in spring and summer.In autumn it is eutrophication.Combined with the features and conditions in Yuqiao Reservoir,to alleviate the current eutrophication condition,it is suggested that exogenous nutrient input should be controlled and we should reduce the release of endogenous nutrient in Yuqiao Reservoir.The AGP experiment results showed that when N/P ratio were more than the Redfield ratio,we should control the nitrogen input in order to avoid water blooms. |
