Phosphorus Fractions And Phosphate Sorption-Release Characteristics Of The Surface Soil In Water-Level-Fluctuating Zone Of Three Gorges Reservoir

After construction of three gorges project, it will regulate water level ofThree-Gorge Reservoir through the method of accumulating clear water and dischargingmixing water, and form water-level-fluctuating zone（WLFZ）,the total area of which areover348.93Km²and the fall is about30m. When being submerged, soils in waterfluctuation zone will release nutrients such as nitrogen and phosphorus to waters insuitable conditions,have a certain impact on water body. P is one of the main elementsand limiting factor that cause eutrophication of fresh water.So it has important practicalsifnificance for the control of entrophication to study the phosphorus fractions andmigration and transformation of the surface soil in WLFZof Three Gorges Reservoir.So in this paper, the author selected18sites’ soil in WLFZ of Yangtze River and itstypical tributaries from Wushan-Chongqing urban area,analysised their phosphoruscontent and fractions,selected8typical sites to analysis the phosphate sorption andrelease characteristics of the surface soil in WLFZ.The main conclusions have beenreached as follows:1) In research areas,the variation range of total phosphorus content in WLFZ was0.35-0.84g/kg,and its mean was0.61g/kg.The difference of soil TP among differentsoil types is obvious,the TP in yellow soil is higher than mean in research area.TP inYangtze River is higher than tributaries.Total phosphorus content in WLFZ reduced during the non-flooded period in2010as “phosphorus source” and increased during the non-flooded period in2011as“phosphorus pool”and reduced during flooded period as “phosphorus source”. Compareto the non-flooded soil,the soil in WLFZ had lower total phosphorus content andhigher coefficient of variation,that suggested periodic flooding caused soil phosphorusand increased the spatial heterogeneity of phosphorus distribution.2) In research areas, P-fractions were in the order of Ca-P>OP>Fe/Al-P, Ca-Pcontent accounted for56.9%of the total phosphorus content, that suggested Ca-P whichhad the lowest impact on water body was the main fraction in WLFZ. The difference ofsoil phosphorus fractions among different soil types is obvious, Fe/Al-P and OPcontents were higher in yellow soil;besides Pengxi and Ganjing basins,other basins allhad higher Fe/Al-P and OP content than Yangtze River.Phosphorus forms content in WLFZ both changed little during the non-flooded period in2010and increased during the non-flooded period in2011and reduced duringthe flooded period that increased the release risk. Different forms phosphorus content inWLFZ both reduced during flooded period,that suggested during the flooded periodsoils in water-level-fluctuating zone released more phosphorus than absorbed.3) The sorption isotherms of phosphate on the different soil in WLFZ were similarand fitted Langmuir model well. The maximum phosphate sorption capacity Q_maxvariedfrom137.79mg/kg to88.21mg/kg and its mean was402.0mg/kg;the adsorptioncoefficient varied from0.27L/mg to1.93L/mg and its mean was0.84L/mg;themaximum buffer capacity varied from93.64L/kg to382.34L/kg and its mean was260.31L/kg. The phosphate sorption kinetic on soil in WLFZ inncreased rapidly withtime increasing within12h. After12h, the sorption process reached to equilibrium.Themaximum sorption rates varied from24.4mg/kg·h to90.9mg/kg·h and its mean was60.64mg/kg·h. The maximum sorption rate had a significantly positive correlation withthe percentage of silt and significantly negative correlation with the percentage of sand,this indicated that the quick phosphate sorption of the soils in WLFZ was mainly thephysical sorption process.The phosphate release kinetic on different soil in WLFZ were similar and bothfitted index kinetic model well. The maximum phosphate release capacity varied from1.67mg/kg to7.08mg/kg and its mea was3.39mg/kg; The maximum release ratevaried from0.30to1.36mg/kg·h and its mean was0.88mg/kg·h. The maximumphosphate release capacity had significantly positive correlation with the contents ofFe/Al-P and OP,and better with Fe/Al-P,this is because Fe/Al-P and OP are thephosphorus fractions which are easily released to water body.This thesis results can provide theoretical basis and scientific evidence for thepollution control and supervise of soil in WLFZ of Three Gorges Reservoir.