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Three Gorges Reservoir has built and sluiced in 2009, there has formed a 30 meters hydro-fluctuation belt that the seasonal fluctuation opposite with natural river between the altitude 145 meters and 175 meters. The existing terrestrial ecosystem turns into land and water alternating ecological environment system. A lot of N, P nutrients element, inorganic and organic contamination come into water form soil. That will trigger eutrophication, water pollution, water quality deterioration and so on. And after the reservoir built up, Yangtze River will become a natural river to typical channel type seasonal-regulated reservoir, even a huge artificial lake. Especially the backwater tributaries, their flow rate are degressive, the ability of reaeration, admiting BOD, self-dilution and purification are weakened, the time of contamination retention extended. All these will accelerate the process of eutrophication and water quality deterioration in Three Gorges Reservoir. P is one of factors of trigger eutrophication. The submerged purple soil is rich in P and the terrain is flat, the history of cultivate is long, exogenous P is enrichment in soil. all these are increased the risk of P coming into water from the soil.After Three Gorges Reservoir built and sluiced and Hydro-fluctuation Belt formally formed, the archaic entironment background data will disappear, some important data will be unobtainable. It will create obstacles even irreparable loss for future research and cause some studies could not start. Therefore, studing the Hydro-fluctuation Belt soil before Three Gorges Reservoir is submerged has a very important scientific value and economic, social, ecological immediate significances. And it seems a very tight schedule.The research area of this paper is Xiaojiang river basin hydro-fluctuation belt in the three gorges reservoir. The paper studied the basic physical and chemical properties and inorganic phosphorus morphology, timely collected valuable data, analyzed the potential environmental harmfulness of soil phosphorus to Xiaojiang river. It is the foundation of future research and scientific basis of hydro-fluctuation belt environmental protection. The results are: The sampling area soil mostly are sandy loam soil, clay content is very low, the variation range of density is large, density first is reduce and then is raise with the increasing altitude, the porosity is contrary; Soil pH is essentially neutral to alkaline, the surface layer’s is lower than bottom’s and basicity is enhancing with the increasing altitude; the content of organic matter and phosphorus is higher, and the content of nitrogen and kalium is lower relatively, because of the soil quality, farming systems, and fertilization, but the content gradually decreased along with the increasing depth in the soil profiles, and, the content of organic matter and kalium are decreased along with the increasing altitude, the content of phosphorus and nitrogen doesn’t show a certain degree of regularity.The inorganic phosphorus in the soil profiles of xiaojiang river basin hydro-fluctuation belt in the three gorges reservoir is the main body of phosphorus, the percent of inorganic phosphorus content in topsoil is larger than the bottom soil, the percent of organic phosphorus enhance with the increasing depth in the soil profiles. The content of inorganic phosphorus morphology, Ca10-P is the highest, over 60%, followed by O-P, Al-P and Ca2-P, Cag-P and Fe-P is the least, besides gaoyang town; in gaoyang town, O-P is the highest, about 40%-70%, followed by Al-P, Ca10-P, Ca2-P and Ca8-P and Al-P is the least. The exhibition of inorganic phosphorus morphology and organic phosphorus isn’t accord in the soil profiles and altitude, circumstance is complicated. Through correlation analysis, showed that Ca2-P, Al-P and Ca8-P are the main sources of available phosphorus, O-P was an important source, while the Fe-P and Ca10-P are smaller contribution to the available phosphorus. And organic matter and pH increased or decreased the effectiveness of phosphorus by influencing the content and forms of inorganic phosphorus.With the temperature is lower, less phosphorus can be adsorb and more phosphorus can be coming into water from soil. At the altitude 145-155 meters, the time of soil submergence is about 6-9 month, the content of inorganic phosphorus morphology which easier translating into the enterable in water morphology is higher, at 239954.76 mg/m2, the harmfulness of eutrophication is larger. At the altitude 155-165 meters and 165-175 meters, the time of soil submergence is shorter than 145-155 meters, but it is all in the chilly months, the contents of inorganic phosphorus morphology which easier translating into the enterable in water morphology are 225273.82mg/m2 and 245715.63 mg/m2, the harmfulness of eutrophication could be appreciated, and we should make preventive measures and prevent from eutrophication.In this paper, I put forward my views and suggestions on the basis of the above, and look forward to having some reference to prevent and control the eutrophication and resolve of the environment of agricultural production of the drawdown areas in Three Gorges reservoir areas.
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