A Study On The Effects Of Sediment Deposition To The Plankton Of The Three Gorges Reservoir

Plankton plays an important role in the material cycle of the water ecosystem and the flowing of energy. So far at home and abroad, most of the studies about plankton have been focused on the quantity, the ecological characteristics,the evaluation of the water quality, etc. Only a few studies had been about the impact of the sediment deposition on plankton. Therefore, it was significant to study the impact of the sediment deposition on plankton. During November 2006 and November 2007 we had investigated the water characteristics, plankton and the sediment's content of the Three Gorges reservoir between Chaotianmen and Tai ping xi river four times, and learnt their changed in time and space. After analysing the data gained, we found out the mutual ralationship between the sediment deposition and plankton, which can provide a scientific basis for better protection of the water environment in the Three Gorges Reservior area.1 the law of the sediment's changed in the waters studiedThe sediment deposition was very obvious from Chaotianmen to Zigui river. The sediment between chaotianmen and yunyang river depositted very fast. After the sediment move to the Yunyang, the speed tended to slow down and maintain a certain range. From the deposition of sediment, we can conclude the size of sediment was larger in the flood period than in the dry season. It was the same as the feature of the sediment's content in the water. The quantity of the sediment changed as the seasons changes;the sediment content was high in rainfall season but low in dry season.2 on the waters of sediment deposition on the impact of sediment deposition on the changes of water's index in waters studiedBecause the instruments in the experiment were inadequate, we could not get sufficient data about the impact of the suspended sediment's deposition on the PO₄³-P, NH₄^--N, NO₂^--N in the water of the Three Gorges Reservoir between Chaotianmen and Zigui river, which needs further research; the diversification trend of the NO₃^-- N, T, DO, pH and electrical conductivity, and other indicators of water quality sampled the four times was nearly the same. 3 the impact of the sediment deposition on phytoplankton in the waters studiedThe survey of phytoplankton's species composition showed that at the four sampling situses the phytoplankton was very rich. During the study period, the total of the phytoplankton species discovered was seven phylum,58 category and 183 kinds. Most of them belong to Cyanophyta, Bacillariophyta and Chlorophyta. The composition of the phytoplankton's species sampled in four times appeares the same trend-algae's species are from less to more, but the categories of species are from less to more, and the biomass was also gradually increasing. At each sampling situs the most were Cyanophyta, Bacillariophyta and Chlorophyta. Along the direction of the current, Xanthophyta,Cryptophyta,Euglenophyta and Pyrrophyta gradually increase. The three sampling results in the dry season with low sediment content showed that the dominant species of phytoplankton transforme gradually from Bacillariophyta to Chlorophyta or Cyanophyta, but the sampling results in the flooding period with high sediment content showed that the dominant specy of phytoplankton at each sampling situs is Bacillariophyta except Wanzhou,Shizhuand Wushan. From Chaotianmen to the Three Gorges Reservoir area in Zigui river the average annual biomass of phytoplankton was gradually increasing along the current direction, and the diversification tendence of the phytoplankton's density and biomass becomes in a line. From Chaotianmen to Zigui,the Shannon-Weaver diversity index of phytoplankton changes undeely.4 the impact of sediment deposition on zooplankton in the waters studiedAccording to the results of the experiment, we had learnt that the species composition of zooplankton sampled had the same tendence-the species was from less to more, and the biomass was also gradually increasing. Particularly Copepoda had increased significantly in the type and quantity. The main of zooplankton at each sampling situs were protozoa and rotifers. The species composition of the zooplankton changed Contrarily to the phytoplankton .Sediment deposition had important influence on the types of zooplankton. The types of zooplankton gradually increased with the gradual deposition of sediment. The biomass of zooplankton changed relatively intensely, especially Cladocera,Copepoda and Young animal, and the biomass of the zooplankton will gradually increase.On the one hand was conducive to the growth of plankton and by increasing the transparency. On the other hand, it may lead the nutrients depositing so as to induce the detriment of plankton's growth. The results of the experiment showed that the sediment deposition from Chaotianmen to Zigui river of the Three Gorges Reservoir area was conducive to the growth of plankton.