Studies On The Plankton In The Cage Culture Section Of Wanzhou Region Of The Three Gorges Reservoir

The plankton was playing an important role in the matter cycling and energy flowing of water ecosystem. Most past researches on the plankton at home and abroad focused on the quantity, ecological characters, water quality evaluation, etc. And little researches about plankton had conducted in the rivers with cage culture. This paper deals with the species, the density and biomass, the classified distribution of the plankton in the water area where cage culture was taken, in Wanzhou region of the Three gorges reservoir, based on the investigation from May, 2005 to July, 2006.1,the variations of the phytoplankton in researched area153 species of the phytoplankton were identified, which belong to 7 divisions, 42genus. Bacillariophyta, Cryptophyta and Euglenophyta took the dominant species of the phytoplankton. It's different from the situations in other reservoirs and lakes, in which Bacillariophyta and Chlorophyta were the main groups of phytoplankton. There was no significant relationship between biomass and the density of the phytoplankton in upper reach and lower reach of cage area, so was not in the controlled area. But there was significant positive relationship between the biomass and the density of the phytoplankton in cage area. The biomass of the phytoplankton were significantly difference in six sampling stations.The biomass of the phytoplankton in the lower reach of cage area was more than that in upper reach, and the latter was more than that in cage area, the biomass in cage area was more than that in controlled area. The number of the species of the plankton in upper reach of cage area was more that in cage area, the number in cage area was more than that in controlled area, the number in controlled area was more than that in the lower reach of the cage area. In four seasons, the biomass of the phytoplankton in summer was more than that in spring, the biomass in spring was more than that in fall, the biomass of the phytoplankton in fall was more than that in winter. The number of the species of the plankton in summer was more that in fall, the number in fall was more than that in spring, the number in spring was more than that in winter. In water level change, the biomass in abundant season was more than that in normal season, the biomass in normal season was more than that in dry season. The number of the species of the plankton in normal season was more than that in abundant season, the number in abundant season was more than that in dry season. The diversity indexes of phytoplankton in cage area were more than that of other area. The classified distribution of the phytoplankton showen that the medium-sized species, whose diameters were 20～50μm, took the absolutely dominant in the biomass of the phytoplankton. This was not quite fit with the result of water quality evaluation by species and biomass, mainly because of the plentiful sand in the water and the unstable water level in the three gorges reservoir. The results indicated that it's being worth studying if the index was suitable for evaluation the water quality of this kind of rivers. So cage culture had increased biomass of phytoplankton.2,the variations of the zooplankton in researched areaBoth the biomass and the number of species of the zooplankton were fewer and stable. Protozoa and Rotifer were the dominant groups of the zooplankton. It's different from the situations in other reservoirs and lakes, in which Rotifer took the dominant species. The biomass of the zooplankton in upper reach of cage area was more than that in lower reach, the biomass in lower reach was more than that in cage area, and the biomass in cage area was more than that in controlled area. And the number of the species of zooplankton in upper reach of cage area was more than that in cage area, the biomass in cage area was more than that in controlled area, the biomass in controlled area was more than that in lower reach. In four seasons, the biomass of the zooplankton in summer was more than that in spring, the biomass in spring was more than that in fall, the biomass in fall was more than that in winter. And the number of species of zooplankton in summer was more than that in fall, the number in fall was more than that in spring, the number in spring was more than that in winner. The biomass of the zooplankton in abundant season was more than that in normal season, the biomass in normal season was more than that in dry season. And the number of species of zooplankton in normal season was more than that in abundant season; the number in abundant season was more than that in dry season. As the influences of the hydrodynamic conditions, the relationship between the biomass of phytoplankton and the zooplankton was not same as other lakes and reservoirs. There were significant positive correlation between the biomass of the phytoplankton and the zooplankton in stations I,III,IV and V, but it was no relevance in stations II and VI.The research presents that cage culture had increased the biomass of zooplankton.