Studies On Community Structure Of Zooplankton In Dianshan Lake

Dianshan Lake is the largest freshwater lake in Shanghai as well as the water resources protected field in Huangpujiang river, and its water quality and quantity is of great importance to the water safety of Shanghai. In the past several years, the water quality of Dianshan Lake has been deteriorated, of which the index of water quality decreased fromⅡ-grade level to V-grade level or inferior V-grade level.So the government of shanghai payed great attention to the pollution control and water resource protection. In recent years, the local government took some measures to stable the water quality, but eutrophication trend has not been prevented.Especially in summer, blue algae was bloomed seriously in part of the lake which affected the safety of drinking water in Shanghai and landscape in this area. A series of experimental projects should be proposed in order to prevent the eutrophication in the whole lake. Therefore, experimental projects that control eutrophication and prevent algal blooms were built by integrating biological treatment technology and inner pollution control technology in typical water areas of Dianshan Lake since first half year of 2008.In this paper, the community structure of zooplankton including species composition, standing crop dynamics and diversities were studied monthly in Dianshan Lake from October 2008 to October 2009.We also analyzed the correlation between zooplankton community and environmental factors. Based on the difference of zooplankton community which inside and outside the demonstration projects of ecological restoration, we preliminary discussed the response of zooplankton community to the demonstration projects of ecological restoration. The main results are as follows:1.A total of 80 species were identified, including 46 Rotifera (58%) belonging to 18 genera of 10 families,21 Cladocera (26%) belonging to 10 genera of 6 families and 13 Copepoda(16%) belonging to 11 genera of 6 families.Species composition of zooplankton was differently in different seasons. The number of species of zooplank- ton was largest in summer, lowest in winter.Rotifer was dominant species in four seasons.2.The dominant species of the zooplankton were Keratella cochlearis, K.valga, Brachionus calyciflorus, B.angularis, Polyarthra trigla, Bosmina longirostris, B.coregoni, Moina micrura, Microcyclops leuckarti, Schmackeria forbesi and Sinocalanus dorrii.3.The average zooplankton density were 356±334ind./L. The maximum value (1260 ind./L) occurred in May 2009, and the average zooplankton density were 12.67±12.53 mg/L, and the maximum value (40.85mg/L) occurred in July 2007.In the horizontal distribution, the highest standing crops appeared at Sampling site S11, and the corresponding mean density and mean biomass were 208 ind./L and 2.77mg/L respectively. The lowest mean diensity appeared in sampling site S9, and the value was 208 ind./L. The lowest mean biomass was only 6.91 mg/L that occurred at Sampling site S7.4.In the horizontal distribution, annual average Shannon-Weaver diversity index of zooplankton ranged from 1.566 to 1.856 in different sampling sites. In the monthly variation, the ranges of average values of Shannon-Wiener index (H) in Dianshan Lake were 0.910～2.187 with a mean value of 1.718.According to the standards about evaluation of the quality of water, the Dianshan Lake could be regarded as a mesosaprobity.5.According to the Pearson correlation analysis results, there was a significant negative relationship between the species of zooplankton and the content of Ammonia Nitrogen, Total Nitrogen, BOD5 in the Dianshan Lake.The water temperature significant correlated positively to the number of species of zooplankton. Pearson correlation analysis showed that both the zooplankton community density and biomass negatively related to the phytoplankton density. The zooplankton density also has negative relationship with the number of species of Cyanophy.6.The species composition and density of zooplankton inside the Oriental Land algal control area were not significantly different from those outside the fence.In conclusion, the diversity of zooplankton in Dianshan Lake has the trend of decline, the abundence and biomass of zooplankton were greatly affected by eutrophi- cation. Zooplankton community was no obviously affected by ecological restoration demonstration project, the blooming of algal has an influence on the growth and reproduction of large zooplankton crustacean, while in favor of small size species, because large size Cladocera can filter algal better, we should rehabilitate the structure of zooplankton community in Dianshan lake in combination with fish control, zooplankton species introduction and hydrophytic vegetation reconstruction.