Research On The Soil Phosphorus Distribution And Change Characteristics Of Different Type Of Slope Land In Xiaojiang River Drawdown Areas In The Three Gorges Reservoir

Three Gorges Project is the largest water control project in the world at present. The reservior areas will adopt the "storage in winter and discharge in summer" attemper manner of water-level, in the effort to bring into play on the compositive function of controling and preventing floods,power generation,shipping,and at last, has fromed a 340 square and 30 meters drawdown areas between the altitud 145 meters and 175 meters.This is a sensitive terrestrial-aquatic transverse zone which had ever seen in the Yangtze river history,It possess of more of precious land resourse,has formed different shape of slope land,which have the value of a agriculture and forestry,andis under threat of Geological Disasters.At the same time, it also the collection and fountain of major factors Nitrogen, phosphate and potassium for eutrophication.This especial wetland ecological system is a typcal fragile Eco-regions.P is not only the indispensable nutrient to make the plants grow,but also one of factors of trigger eutrophication. After Reservoir construction, it will submerge more Purple soil which is rich in P originally,and enriehment exogenous P because of the flat terrain and the long history of eultivate, all these are inereased the risk of P coming into water from the soil.The search area of this paper is Xiao jiang river basin drawdown areas. Firstly,the slope shape of drawdown areas has been divided into three:the gentle slope bedrock and earth slope; the naked rock slope; the silting beach slope. on that basis,this paper studied the distributional and change characteristics of the Soil Phosphorus in different elevation,different slope shape, different land use.It emphasize the the inherence affiliation beeween the slope shape and the Soil Phos orus distributional and change characteristics.The results are:1. Through the analysis on the data of P,this paper research into the distributional characteristics of different slope shape.the result shows:phosphorus of the gentle slope bedrock and earth slope changed by a large margin,because of the very rich plant species and the intense human disturbance, therein,the high efficiency type of inorganic phosphorusCa2-P,Al-P,Ca8-P, and high activity type Fe-P proned to accumulate in the soil, and it will enhance the threat of eutrophication; the naked rock slope is lack of soil,so the content of avaliable phosphorus and a water-soluble phosphorus is small,the change margin is low; phosphorus of the silting beach slope reduced,these are related to the intense water-soil effect in the water-soil boundary.But with the development of Drab Soil,the avaliable phosphorus showed escalating trend.2. Through the contrast analysis of the data in the same place in 2008 and 2009,the result shows: due to the surface layer soil with higher organic matter had been denude, add the influence of sediment deposition,the total P, available P reduces. On the one hand different slope shape has also impair the inorganic phosphorus in soil:the content of high water-soluble type Ca2-P and high activity type O-P reduces; inorganic P content in the gentle slope bedrock and earth slope decresa in rice rate,due to the high enrichment of water-soluble types of inorganic phosphorus,so enhance the risk that P dissolve to water; in the low altitudes silting beach slope, where growed aquatic plants and wetland plants,due to the screen function,it will ease the risk of eutrophication. On the other hand, periodic alternation of wetting-dry has also impair thechange of inorganic phosphorus in soil: the content of Ca2-P,Ca8-P,Al-P,O-P will decreaase in the dry environment,and the Fe-P increase;in the wet environment, Fe-P will transform the high activity type Ca2-P,and transmit in the form.In the low altitudes, where have been wetting-dry many times,the release P from the soil to water is evidently,add to the detroy of plants,so the high efficiency type of inorganic P Ca2-P,Al-P,Ca8-P, and high activity type Fe-P proned to release to water, and it will enhance the threat of eutrophication.3.Through eorrelation analysis on the data in 2008 and 2009,showed that Ca2-P, Al-P,Ca8-P are the main sources of available Phosphorus, Fe-P was an important source, while the other types of inorganic phosphorus are smaller eontribution to the available Phosphorus.To the different type of slope land, we should adjust measures to local conditions,and use it in reason。I put forward my views and suggestions on the basis of the above research result, and look forward to offering some reference to prevent an control the eutrophication and advance the sustainable utilisation of the different shape of slope land in the environment in Three Gorges reservior areas.