The Primary Studies On The Changes Of Phytoplankton And The Environmental Factors In The Estuary Of Yangtze River

In this study, the changes of phytoplankton and the environmental factors are studied in the Estuary of Yangtze River. Especially based on the analysis of estuarial research data of May and August, 2003, the ecological characteristics of phytoplankton including community composing, number and diversity are studied. Multivariate analysis methods including Cluster analysis, multidimensional (MDS) analysis, principal components analysis (PCA) are used to explore the phytoplankton community structure and its influencing factors. In comparing with historical data, the effects of the deepwater channel to the ecological environment of Yangtze Estuary are analysed. The main conclusions as follows: In May and August, 2003, 54 species of phytoplankton are identified, They belong respectively to Chrysophyta, Cyanophyta, Bacillariophyta and Pyrrophyta. Dominant species include Coscinodiscus asteromphalus, Skeletonema costatum, Melosira granulata etc. Most of which are belong to Chrysophyta. The average numerical abundance of phytoplankton in summer(7.0×10⁵ind/m³) is higher than that in spring(3.4×10⁵ ind/m³). Perhaps it is because the weather in summer is suit for the growth of phytoplankton.In different part of Yangtze Estuary, phytoplankton community structure is different. Diversity index of phytoplankton in flood period is higher than that in dry period. Species diversity(H) and homogeneity(J) are subtractively correlated with surface salt(r=-0.51, -0.58), and positively correlated with NO₃-N(r=0.51). Margalef index(D) is significantly and positively associated with the number of species of phytoplankton(r=0.84). The results implied by the three separate indexes such as Shannon-Wiener Index, Margalef Index and Evenness Index of phytoplankton trends to identical. They can all well reflect the situation of biodiversity of phytoplankton of research area. Community structure of phytoplanktonMultivariate analysis (MDS, CLUSTER, ANOSIM) by using software PRIMER 5.0 on the phytoplankton shows that the 20 sites can be classified into three groups (TWIN â… , â…¡, â…¢) by the cluster analysis based on species composition. The dominant species in three groups differ from each other. Salinity and turbidity are the key environmental factors caused the differences.PCA analysis of the environmental factors shows that significant differences among 20 sites existed in nutrients, salinity and turbidity. The content of nutrients is reducing as the salinity increasing during the commix process of fresh water flowing from Yangtze River and seawater with higher salinity and lower nutrients.Phytoplankton and environment factors variety in 5 yearsPhytoplankton of Yangtze Estuary can be classified into three components: fresh water component, estuarial and coastal component and a high Salinity component. Estuarial and coastal species are the main part of phytoplankton communities, which dominates the community feature of Yangtze Estuary.The influence of the Yangtze Estuary deepwater channel on the quantity of phytoplankton is not distinct. But species diversity (H) declined under the influence of Yangtze estuary deepwater channel, especially in site A9, All, A13, A15.The PCA results on the varieties of environmental factors of the main sample sites outer the channel and all sample sites inner the channel show that the annual fluctuation of the chemistry index of main sample sites outer channel is not significant, but the trend of turbidity increasing is very distinct. It is obviously that the Yangtze Estuary deepwater channel caused the results. Forecast and prospectThe deepwater channel project of Yangtze Estuary will remarkably change the moving state of water and silt, alter the transportation amount of nutrients, which also has a notable or latent effect on the faraway ecosystem and environment of the Estuary of Yangtze River. The influences of water conservancy projects on ecosystem and environment of river estuary are long-term, slowly, potential and extremely complicated, and are comprehensive effects of all projects on them. Following the tracks of projects, monitoring, evaluating and analyzing the response of river estuary will provide a scientific basis for the protection of ecological environment of later construction of water conservancy projects.