Community Structure of the Crustacean Zooplankton in Tangpu Reservoir

Tangpu Reservoir fulfils several important social functions including water supply,flood control and water environment improvement. The study on the population dynamics of crustacean zooplankton in Tangpu Reservoir is a significant environmental monitoring effort that supports efforts to prevent eutrophication of Tangpu Reservoir.Monthly investigation of the community structure of crustacean zooplankton was performed at six sample sites in Tangpu reservoir from January to December 2011,with study emphasis on species composition,density and diversity of crustacean zooplankton. The sampling sites represent a range of zones: littoral,backwater and pelagic. Crustacean zooplanktons for qualitative analysis were collected using a No. 13 plankton net,fixed with 4% formalin. 20 L water samples for quantitative analysis were collected,filtered through plankton net No. 25( diameter of 64 μm),then concentrated to 50 mL and preserved with 4% formalin. The species identification and quantitative characteristics of crustacean zooplankton samples were determined under microscope and anatomical lens. A total of 52 crustacean zooplankton species including 27 cladocera and 25 copepoda were recorded. The species richness of crustacean zooplankton was the highest in spring,followed by summer,autumn and winter. The density of Cladocera averaged at7. 93 ind /L, with the highest value( 20. 60 ind /L) in July, while the mean density of Copepoda was13. 51 ind /L, with the highest value( 36. 13 ind /L) in November. The highest density of Cladocera( 12.55 ind/L) and Copepoda( 21. 70 ind/L) both occurred at Shuangjiangxi,where the relatively static water and plentiful nutrients supplied by two tributary inflows were beneficial for the growth of crustacean zooplankton.The lowest density of Cladocera( 4. 51 ind /L) and Copepoda( 6. 67 ind /L) appeared at the pelagic area of the reservoir. Margalef index in Tangpu Reservoir was high and the seasonal variation of Margalef index showed the same tendency as species richness,with the highest value 5. 32 in May( spring) and the lowest value 1. 76 in February( winter). The spatial distribution of the Margalef index ranged from 3. 97 to 4. 96,with the mean value of4. 53; the highest value occurred in Qushuikou( 4. 96) and the lowest in Wanghuaxi( 3. 97). The evaluation based on Margalef index and related literatures suggested that the water quality in Tangpu reservoir is mesosaprobic-oligosaprobic.