The Study Of Silicon Distribution, Budget And Circle In The Three Gorges Reservoir

Construction of irrigation works (dam, reservoir) always impact on hydrological conditions and ecosystems in the region, which can change the current and nutrients exchange in the river. Three Gorges Dam is the biggest irrigation works in the world. Within rising water level, stream is moving more slowly, resorting time of water is longer, and sinking sand is more. The various changes of hydrodynamics in Yangtze River main stream will impact silica seriously in consistence, structure and distribution. This paper is based on investigation at Yangtze River in April 2006, September 2006 and April 2007, researches on distribution and transformation character of silica in Yangtze River and Three Gorges Reservoir. Refer to historical data, this paper also researches on the budget and circle process, estimate on silica retention in Three Gorges Reservoir.Dissolved reactive silica (DSi) and suspended particulate matter (SPM) in Yangtze River main stream reduce rapidly between Fuling City and Three Gorges Dam. In middle and lower reaches of Yangtze River, the concentration of DSi and SPM rise because of supply from Dongting Lake, Poyang Lake and Hanjiang River. The distribution of biogenic silica (BSi) is lower in upriver area before Dam and higher in middle and lower reaches of Yangtze River.The research in dry season in run of river of TGR, the suspended particulate matter has obvious reduced along Yangtze River main stream. The content of suspended particulate matter falls rapidly between Mutong and Wanzhou, while stabilized between Wanzhou and Three Gorges Dam. This indications aggradation character of Three Gorges Reservoir, most of suspended particulate matter falls rapidly in the transitional zone in the reservoir and the suspended particulate matter in the lacustrine zone comparatively keeping a high level, may indicate the suspended particulate matter spontaneity and aggradations in the reach. Vertical distributing shows that concentration is comparatively low in surface layer and comparatively high in bottom layer.The concentration of BSi is uniformly in Three Gorges Reservoir. Dissolved silica concentration is falling along river.The stratification of DSi was not obviously, and no relation with chlorophyll a. This phenomenon indicates: in the Three Gorges Reservoir phytoplankton consume in main steam is not main factor of DSi distributing in Three Gorges Reservoir.Compared with Three Gorges Reservoir, the bays in tributary confluent contain more BSi .Xiangxi River is an example in evidence, BSi concentration is higher than main steam and other bays, and the concentration of BSi have relationship with chlorophyll a in a certain extent. But in other bay, we can't find the same relationship. This phenomenon indicates that the biogenic silica have relationship with not only phytoplankton, but also the content of silica biogenic scraping and the accumulation of suspended particulate matter.With the production, deposition, sediment of biogenic silica and flux of dissolved silica at the sediment-water interface were studied, budget and circle in the Three Gorges Reservoir are described.The present retention of dissolved silica in the reservoir isabout 3%. Compared to total silica load, the retention of biogenic silica in the reservoir is only 5.0%.With its present storage capacity, the reservoir does not play an important role in silica sink.