Phosphorus Release Characteristics At Water Fluctuation Zone Of Pubugou Reservoir In Hanyuan And Risk Identification

Combined with previous researches, collecting 6 typical soils at water fluctuation zone of Pubugou reservoir in Hanyuan,through the release of phosphorus indoor simulation experiment to study phosphorus release characteristics at water fluctuation zone and the relationship between nutrients contents of soil and phosphorus release in alternately waterl-ogged and drained condition, in order to provide a reasonable reference for preventing eutrophication of reservoir water and the scientific development of water fluctuation zone utilization and management. Test measurement and analysis physical and chemical properties of soils and overlying water. The major results are as below:(1)The available phosphorus of soil (Olsen P) is in the 10.23-74.49 mg·kg-1, the available phosphorus and phosphorus release a good correlation, phosphorus content shows that garden plot> dry land> paddy field. Active iron (Feox) content is paddy field> garden plot> dry land, different land uses have a significant effect on soil Feox content, soil activated alumina (Alox) content is in the paddy field> Garden plot> dry land. Dry land, garden soil have a bigger P release risk than paddy field.(2)Phosphorus adsorption isotherms of soil is well fitted using Langmuir equation (r2 =0.95-0.99). The maximum amount of phosphate adsorption of soil (Qm) and phospho-rus adsorption index (PSI) was significantly correlated with correlation coefficient 0.960, PSI can be used as alternative indicators of Qm. Qm of soils is in 625.00-909.09mg·kg-1, the trend is for the garden plot> paddy field> dry land; Purple soil> alluvial soil; K value is paddy field> garden plot> dry land. The largest degree of sorption saturation (DPS) of soils is dry land soil with 10.05, dry land and garden soil's DPS is higher than paddy field soil.Maximum buffering capacity (MBC)of soil and Qm, and adsorption binding energyre-lated constants (K) was significantly positively correlated; Qm, K, MBC with soil organic matter content (OM) was significantly positively correlated; Feox, Alox and K,MBC showed significant positive correlation; DPS significantly negatively correlated with MBC, DPS and K values, soil Feox, Alox significant negative correlation coefficients are-0.795,-0.934 and -0.872. Characteristics of soil phosphorus desorption can be described used Freundlich equation (r2=0.91-0.98), phosphorus desorption parameter (b) and phosphorus retention (f) correlation coefficient r2=0.68.Garden, dry soil P release risk is bigger than paddy soil, purple soil is bigger than alluvial soil.(3)RP (<0.45) concentrations of overlying water increases with the time increasing at water fluctuation zone, in flooding conditions, Fe-P, Al-P and Ca-P are dissolved. When the addition of external phosphorous> 100mg (P)/kg, the P concentration C RP(<0.45) in overlying water tends to balance in the first 30 days of flooding. The size of release of soil phosphorus garden plot> dry land> paddy field. Alternately waterlogged and drained condition has certain activation to soil phosphorus; Balance of the timeof phosphorus con-centration of overlying water flooded the second time is shorter compared with the first flooding. C RP(<0.45) and Pi show exponential relationship, two flooding times reached a significant positive correlation (r2= 0.51-0.79),dry land, garden soil has a greater risk of phosphorus release.(4)Flooding can improve the content of the soil Feox, Feox content of flooding dried soil decreased to the level before the flooding. Range of Feox Change after flooding is dry land> paddy field> garden plot, purple soil> alluvial soil. DPS of the soil is closely related to Feox and Alox. The maximum amount of phosphate adsorption of soil increased to the highest is 2758.01 mg·kg-1 in flooding time at water fluctuation zone of Pubugou reservoir in Hanyuan, Qm, MBC, soil phosphorus sorption index (PSI) value increased after flooding. Flooding can significantly increase soil P buffer capacity, improve buffering capacity and the maximum adsorption capacity of the soil. Flooding increased phosphorus retention of soil. The reason is that the content of Feox and Alox substantial increased.(5)Total phosphorus concentration in the overlying water (CTPunf.) with Olsen P, the change in Feox and Alox, DPS, MBC is significantly correlated, the correlation coeffici-ents are 0.8126,-0.6350,0.7532,-0.8532. Through the principal component analysis, soil phosphorus release ability of the soil is related to phosphorus supplies and ability of the phosphorus adsorption, key indicators include OM, Olsen P, f, Qm, Feox, Alox and so on, The soil has a larger risk of soil phosphorus release at water fluctuation zone of Pubugou reservoir in Hanyuan.The phosphorus concentration in the overlying water is more than critical concentra-tion of eutrophication which is 0.02 mg·L-1 after 30 days in the flooded. Soil DPS values exceeded the critical value of 0.90, the soil will result in greater risk of phosphorus release when adding external phosphorous at water fluctuation zone. We can use some measures to control the risk of phosphorus release,such as establishment ecological protection areas, controling living and industrial sewage discharge and so on.