Study On The Change Structure Of Phytoplankton Community And Water Quality Evaluation In Dishui Lake And Its Surrounding Waters

Dishui Lake is located in Pudong Qu Lingang New city, Shanghai, which is the largest man-made lake in China, and is the center of Lingang water system. Dishui Lake plays an important role in shaping the urban landscape ecology, and the microclimate. It is directly connected to the future development and tourism of the new city. Furthermore, it can reflect the water quality status of Shanghai. Water in Dishui Lake comes from the surrounding waters. Therefore, the quality of the surrounding waters can influence the water in Dishui Lake. Phytoplankton in Dishui Lake had been sampled from2011to2012. Since April, July, October and December2012, the physical and chemical indicators of Dishui Lake and its surrounding waters had been monitored. Phytoplankton in the surrounding waters had been sampled since January2011to December2012. The community structures of phytoplankton in the lake and the surrounding waters were compared, in order to know the succession of the phytoplankton community structure and its specificity. Furthermore, predict the pollution status of the waters. It provides the biology basis for the water protection and the future tourism development. The main results are listed as follows:1. There are109species of phytoplankton in Dishui Lake, which belong to62genera of8phyla. The abundance of phytoplankton is1304×104ind/L; and the average biomass is5.75mg/L. Chlorophyta is the main phytoplankton, following is Bacillariophyta and Cryptophyta. Phytoplankton biomass has obvious change with seasons, more in winter, less in summer.There are5dominant species in Dishui Lake: Chlamydomonas globosa、Gymnodinium sp.、Cryptomonas erosa、Chroomonas acuta.The community structure of phytoplankton in Dishui Lake is well-distributed.2. There are216species of phytoplankton was identified in the surrounding waters from January2011to December2012, which belong to85genera of8phyla. The average abundance of phytoplankton is1771X104ind/L, and the average biomass is8.83mg/L.There are11dominant species in the surrounding waters:Chromulina pygmaea、Melosira granulate sp.、Cyclotella meneghiniana、Gymnodinium sp.、 Chlamydomonas globosa、Cateria sp.、Scenedesmus quadricauda、Euglena acus、 Merismopedia minima、Cryptomonas erosa and Chroomonas acuta.The dominant species in different site are different, but Gymnodinium sp. Cryptomonas erosa and Chroomonas acuta are the same dominant species in every sampling site.3.Cluster by R software, Dishui Lake and the surrounding waters is divided into5habitats, which had great difference among phytoplankton.5habitats includes Dishui Lake (H1-H8)、biological treatment area (W2)、the sediment river (W1)、Dishui Ruhu river(W3、W4and W10) and Common river(W5、W6、W7、W8、W9、W11、 W12、W13、W14). Among the surrounding waters, the abundance of the phytoplankton in the sediment river and biological treatment area were less than Dishui Lake. However, the abundance of the phytoplankton in Dishui Ruhu river and Common river were more than Dishui Lake.The variation of the dominant species changes with the seasons is obvious in Dishui Lake,the surrounding waters is not obvious.According to the ecological evaluation criterions, the results showed that the water quality of Dishui Lake was at middle-eutrophic eutrophic level. The water quality of the surrounding waters was at eutrophic level.4、SPSS analysis of Dishui Lake and the surrounding waters indicated that major environmental factor which impact phytoplankton density was Chla, and Chla had positive correlation with phytoplankton density.Between physical and chemical factors related to salinity. and conductivity showed a very significant positive correlation, NTU showed a very significant positive correlation between TSS and COD, NTU was a significant negative correlation between conductivity and TN.5、CCA analysis on phytoplankton of different groups indicated that most main phytoplankton species had positive correlation with DO、SAL、TN/TP、WT and pH. Chromulina pygmaea likes living in the environment of low-temperature, low-nutrient, high salinity and high transparency; Gymnodinium sp. is suitable for the growth of high salinity, dissolved oxygen and low temperature environment; Merismopedia Minima and Euglena acus are suitable for high-temperature growth; Carteria sp. is suitable for growth in the environment of high temperature and high nutrients. The study found that high-temperature has large impact on the growth of Chlamydomonas sp.