Assessment of phosphorus release from typical soil types in the zone of fluctuating water level in the Three Gorges reservoir region

The zone of fluctuating water level in the Three Gorges reservoir area is a vulnerable area for non point source pollution according to the special hydrological characteristics and agriculture practices.In the zone of fluctuating water level of the studied Three Gorges Watershed,ten typical soil samples with four soil types and four patterns of land use are selected.The simulative study on the risk of submerged soil phosphorus leakage to the reservoir is conducted.Under the submerged simulation with the phosphate concentration of the solution,ranging from 0.1 mg/L to 1.6 mg/L,the interactions of soil and phosphate of water are divided to three patterns:release,sorption,and combination of release and sorption The patterns are distinguished by the relationship between the equilibrium P concentration at zero sorption(EPC₀) and the phosphate concentration of solution With the significantly relat ivity between EPC₀ and Olsen-P,Olsen-P is used as an index which provides the thresh old of three patterns When Olsen-P of soil is lower than 14.4 mg/kg,EPC₀ of the soil is lower than 0.1 mg/L,then the soil will absorb the P of native water,and this type of soil is the sink of P.When Olsen-P of soil is beyond 123 mg/kg,EPC₀ of the soil is higher than 1.6 mg/L,then the soils P will be released to the native water When Olsen-P of soil is between 14.4 mg/kg and 123 mg/kg,the soil will release or retain phosphorus according to the PO₄^3- concentration in native water.