Research On The Chief Zooplankton Community In Dishui Lake And Its River

Dishui Lake is located in Lingang New City, Pudong New District in Shanghai. Excavation of the lake began in June2002and was finished in October2003. It is the largest man-made lake in China with the square measure5.56km2and the mean water depth3.7m.As a new-constructed man-made lake, Dishui Lake undertakes the function of water exchange and flood control and drainage. Meanwhile it plays an immeasurable role in shaping the ecological urban landscape and optimizing the regional climate. Environmental factors and community structure of chief zooplankton in Dishui Lake and its river course were studied monthly from January to December in2010in this research. There were6and5sampling points in the river course and the lake area respectively. Differences and causes of the chief zooplankton community in the river course and lake area were analyzed. Relationship between the zooplankton community and physicochemical factors of the water was discussed. Water quality of Dishui Lake and its river course was evaluated considering TLIc, indicator organisms of rotifer and species diversity index. The research was aimed at providing biological basis for the lake management and ecological environmental protection. Meanwhile, it could accumulate data for researching the law of long-term evolvement of man-made lake ecosystem. The main results of this research were as follows:1. In the annual survey in2010,59species of chief zooplankton group were identified, belonging to18families and40genera. There were35species of rotifer belonging to7families19genera,11species of copepod belonging to5families9genera and13species of cladocera belonging to6families12genera. There has occurred32and57species in the lake area and river course respectively. The species richness in the river course was higher than in the lake area. Rotifer was dominated in the zooplankton species composition both in the lake area and in the river course. Seasonally, the maximum species number occurred in May both in the river course and in the lake area and the number was26and18respectively. The minimum number in the river course was15, occurring in November and the minimum number in the lake area was4, occurring in December.2. Uniform annual values (UNV) of density and biomass of chief zooplankton community in the river course were840.7lind/L and765.02×10-3mg/L and the values in the lake area were439.5ind/L and351.4×10-3mg/L, values in the river course being higher than in the lake area. Horizontally, the maximum UNV of density (1198.33ind/L) and biomass (1154.30×10-3mg/L) occurred in the5th and2nd sampling points respectively in the river course; the minimum UNV of density (328.11ind/L) and biomass (251.83×10-3mg/L) occurred in the9th and11th sampling points respectively in the lake area. Rotifer played the most important role in the zooplankton standing crop. Seasonally, the maximum density (2320.61ind/L) and biomass (2339.08×10-3mg/L) occurred in May and the minimum values (64.58ind/L and54.86×10-3mg/L) occurred in November in the river course. The maximum density (1384.36ind/L) and biomass (993.10×10-3mg/L) occurred in May and August respectively in the lake area and the values were lower than the river course. The minimum density (4.65ind/L) and biomass (7.58×10-3mg/L) occurred in December in the lake area and the values were much lower than the river course.3. In Dishui Lake and its river course, dominant species of rotifer were: Polyarthra trigla, Trichocerca pusilla and Anuraeopsis fissa; dominant species of copepod were:Thermocyclops brevifurcatus, Mesoclops leuckarti and Sinocalanus tenellus; dominant species of cladocera was:Moina micrura.4. Pearson correlation analyses indicated that:seasonally, rotifer density was significantly positively correlated with the value BOD5and an extremely significantly positive correlation between rotifer biomass and BOD5was also detected in the river course; density of copepod was significantly positively correlated with the water temperature (WT) and NO2--N and the correlation between the density of cladocera and NO2-N was extremely significantly positive. In the lake area, there was a significantly positive correlation between the rotifer density and WT and the correlation between the biomass and WT was extremely significantly positive; density and biomass of cladocera were significantly positively correlated with the WT and they also have a extremely significantly negative correlation with the pH. Horizontally, the annual mean of rotifer biomass was significantly negatively correlated with the Total Dissolved Salt (TDS) and pH, while it was significantly positively correlated with NO2--N, and it also had an extremely significantly positive correlation with BOD5; density and biomass of copepod were extremely significantly negatively correlated with pH and TDS and were extremely significantly positively correlated with BOD5and nutritive salts of N and P; density and biomass of cladocera were extremely significantly negatively correlated with pH and TDS and were extremely significantly positively correlated with nutritive salts of N and P. Redundancy Analysis (RDA) revealed that species distribution of chief zooplankton community in Dishui Lake and its river course had the most interpersonal relationship with pH, NO2--N and TDS. WT, pH,BOD5, NO2--N and TDS were the five main abiotic factors that affected the community structure and seasonal succession of chief zooplankton in Dishui Lake and its river course.5. Water quality of Dishui Lake and its river course was evaluated considering TLIc, indicator organisms of rotifer and species diversity index. The results showed that lake area was in light eutrophication level and the river course was in light-middle eutrophication level as a whole.