The Characteristic And Environmental Effect Of Phosphorus Adsorption And Phosphorus Forms In The Three Gorges Reservoir Water-Level-Fluctuating Zone Soil

As the continuous input of P fertilizer in recent years, phosphorus is gradually accumulated in the soils. The lost P from the soils through runoff and leaching waters which can lead to water pollution has been increasingly focused on. After the accomplishment of the Three Gorges Reservoir project, a 30-meter high water-level-fluctuating zone will apear during March to October annually. The zone will be the sink and source of pollutants as the alternately dried and flooding conditions. A mass of pollutants containing P will deposit on the zone, which could be released into water during the flooding conditions. The yellow soil of Pengxi river sediment and purple soil of mountain, taken from Gaoyang country, are used as our research targets. We determined the amounts of amouphous oxides of iron(Feo), free oxides of iron(Fed) and phosphorus extracted by a single extraction of oxalate(P-ox) during flooding conditons, focusing on the characteristic of isothermal adsorption and P-form during flooding conditons. Our research also focused on the relationship between Olsen-P and CaCl2-P, PSR and CaCl2-P. Relative to Olsen P or PSR value, much more P is soluble in 0.01mol·L-1 CaCl2 when the concentration of Olsen P or PSR value exceeds a threshold which could lead to soil P loss to runoff water. The main results are showed below.1) The amounts of amouphous oxides of iron (Feo) increased during flooding conditon, increasing by 6.2% and 10.2% in flooding 15 days comparied with untreated soils. The amounts of crystalline oxides of iron(Fed-Feo) declined up to 13.1% and 17.2% in flooding 20days comparied with untreated soils. The amounts of phosphorus extracted by oxalate(P-ox) increased during flooding conditon, which was related to the increasing amounts of amouphous oxides of iron(Feo).2) The adsorption isotherms of high concentration of phosphorus were L-type on the surface of soil. The Langmuir equation fitting results showed that high adsorption affinity(K) and maximum amounts of adsorption(Xm) in flooding soil, compared to untreated soils. The maximum amounts of adsorption(Xm) of yellow soil and purple soil increased by 70.8% and 16.9% respectively. The adsorption affinity(K) increased of 116.4% and 6.7% respectively.3) The adsorption isotherms of low concentration of phosphorus were different types on the surface of soil. The data of P adsorbed on yellow soil and purple soil were described with linear equation and the Langmuir equation respectively.The native adsorbed exchangeable phosphorus (NAP) and the equilibrium phosphate concentration (EPCo) of yellow soil declined up by 23.6% and 37.0% respectively during flooding condition.Compared to untreated purple soil, the maximum amounts of adsorption(Xm) and Maximum Buffering Capacity(MBC) raised respectively.4) The amounts of Olsen P of yellow and purple soil declined significantly up by 36.0% and 29.5% respectively in flooding 20days. The amounts of Fe-P increased of 10.5% and 33.8% in flooding 15days and the Al-P increased significantly.The amounts of Ca2-P did not change during flooding condition.5) The amounts of Olsen P of yellow and purple soil declined significantly up 30.0%and 32.8% respectively with 0.01mol·L-1 CaCl2 solution in flooding 15days. The amounts of Fe-P increased of 5.5% and 15.6%, Ca2-P increasing of 84.7% and 18.0% respectively. The amounts of Al-P did not change significantly.6) The amounts of Olsen P of yellow soil raised during flooding with 0.1 mol·L-1 KC1, CaCl2 and NH4Cl, adjusted to pH 5 and 9, respectively. The amounts of Olsen P did not change during flooding with 0.1 mol·L-1 KCl and CaCl2 adjusted to pH 7. Compared to 0.1 mol·L-1 NH4Cl adjusted to pH 7, the amounts of Olsen P increased during flooding.7) The two soils exhibit a nonlinear quantity-intensity(Q/I) relationship between Olsen P and CaCl2-P. Relative to Olsen P, much more P is soluble in 0.01 mol·L-1 CaCl2 when the concentration of Olsen P exceeds a threshold that crresponds to where P is less well held by soil than id below the threshold. The two soils also have the thresholds with Olsen-P of 107.7mg kg-1 and CaCl2-P of 2.8mg·kg-1 in yellow soil and Olsen-P of 32.9 mg·kg-1 and CaCl2-P of 2.5mg·kg-1 in purple soil.8) The two soils exhibit a nonlinear relationship between PSR and CaCl2-P. Relative to PSR value, much more P is soluble in 0.01 mol·L-1 CaCl2 when the PSR value exceeds a threshold which could lead to P loss to runoff water.9) The synthetized compound of KFeH14(CPO4)8·4H2O could transformed into KFe3H8(PO4)6·6H2O with 1mol·L-1 AlCl3 or CaCl2 soultions. The synthetized compound of Ca2-P could transformed into Amorphous Fe-P. Amorphous Al-P could not transformed into Ca-P and Fe-P may be transformed into Ca-P. Fe-P and Al-P could transform into each other.