The Ecological Research Of Cladocerans From Maoping To Guizhou In Three Gorges Reservoir After Impoundment

Three Gorges Reservoir is a great water conservancy, its ecological and environmental problems have been much attention. The community of the aquatic life changed a lot with the water ecosystem variation of the reservoir region since the reservoir began filling water. The ecological succession of the Cladocerans since the first impoundment and the effect of the second impoundment on the Cladocerans situation were investigated in Three Gorges Reservoir. The first impoundment began in June2003and the second impoundment began in September2006. We sampled the cladocerans at5transects,14sites from Maoping to Guizhou monthly during June2003to November2006. All that we studied meaned to provide the theory groundwork for the system research of the water ecosystem succession of Three Gorges Reservoir, for the aquatic environmental management, for the using and protecting of the fishery resources.The samples were passed through a zooplankton net of mesh size64μm and material retained was preserved in5%formaldehyde for sorting of the cladocerans from the zooplankton. Among the total of21taxa belonging to five families (Leptodoridae, Sididae, Daphniidae, Bosminidae, Chydoridae), eleven genus(Leptodora, Sida, Diaphanosoma, Daphnia, Simocephalus, Ceriodaphnia, Moina, Bosmina, Bosminopsis, Alona, Chydorus) identified, five species were predominant, which were Bosmina coregoni, B.fatalis, Daphnia hyaline, Bosminopsis deitersi, Diaphanosoma sarsi, four species were common, which were Alona guttata, D. brachyurum, D. leuchtenbergianum, D. longispina. A maximum density of Cladocerans (9.45ind./L) was observed in April2005and the minimum of cladocerans density was found in May2005. The range of cladocerans body length was from0.182to3.575mm, and the average length was about0.3mm, which indicated that the cladoceran community of the front reservoir part was showing the character of miniaturization. The density of each transect that named CJ01, CJ02, CJ03, CJ04, CJ05is respectively1.09,0.34,0.40,0.81,0.50ind./L. The distribution character of the following daphnia such as Bosmina coregoni, B.fatalis, Daphnia hyaline, Diaphanosoma sarsi, D. brachyurum, D. leuchtenbergianum, showed that the transect closer to the dam, the density higher. The converging of the tributaries increased the density of the Cladocerans in the main area of the Changjiang River. In another word, tributary bay was the important source of the zooplankton in the main river. On the other hand, the kinds of the Cladocerans was more from April to July and fewer from November to January, and the annual variation of the density and the biomass showed that the fastigium occurred in April every year, the highest density of2004,2005,2006was respectively7.64,9.45,7.04ind./L. After the second impoundment in September2006, the density reached a small pinnacle (2.76ind./L).The diversity and Pielou index of the cladoceran community were rather low, and the annual average value was respectively1.63,1.01. The values of average diversity index yearly of each transect respectively is1.89,1.86,1.73,1.82,1.71, which showed that the farther from the bam, the lower was the diversity index. Besides, the Xiangxi river matches with the Changjiang River at the left of the CJ04, which resulted in the high diversity index at the left of the CJ04, and also resulted in the higher diversity index in CJ04than CJ05. The annual variation of the average diversity index monthly had several peak values, generally higher in summer and autumn than in winter and spring, so as the Pielou index. The diversity and Pielou index was evidently low in the research region because the several species of Bosmina (its percent89.08%) was taken the dominant position. All that illuminated that the reservoir ecosystem was under the beginning of the evolvement.