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

The Water-Level-Fluctuating Zone(WLFZ)of the Three Gorges reservoir area is a large-scale,unstable new water-land ecotone,serious soil erosion and frequent anti-seasonal dry and wet alternation leading to the loss of soil-water interface material exchange is extremely active,complex.Phosphorus is the main limiting factor of eutrophication,and the process of phosphorus migration,release and transformation in the WLFZ is unclear.In particular,the transition mechanism of the change of phosphorus form and the relationship between source and sink has not been identified.Therefore,it is very important to prevent the eutrophication of the water body in the clear soil and the relationship between source and sink.Based on the soil of the Pengxi River in the Three Gorges Reservoir area,the soils in the fall and fall belts in August 2015 and May 2016 were collected.The main physical and chemical indexes of soil and overlying water were measured.The method of SMT and CJ were used to study the phosphorus The results showed that the adsorption kinetics and adsorption thermodynamics experiments were carried out to solve the phosphorus concentration of the soil in the WLFZ,and the results showed that the phosphorus concentration of the soil was decreased by the different elevation,depth and dry-wet alternation.The relationship between source and sink of soil and overlying water.The main results are as follows:1)The contents of soil organic matter in the fall water of Penghu River were 2.60~10.94mg/g,the mean value was 7.22mg/g,the total nitrogen content varied from 0.27 to 0.39g/kg,the mean value was 0.32g/kg,organic matter and total Nitrogen levels are at a low level.The mean value of total phosphorus is 0.15mg/L,the mean value of dissolved phosphorus is 0.09mg/L,the total nitrogen is 1.39mg/L and the TN/TP is 7~14.It is generally accepted that the TN concentration in the water body reaches 0.2mg/L and the TP concentration is 0.02mg/L,which has a high risk of bloom.The content of TP in the soil of the Pengxi River was 320.27~680.62mg/kg,the mean value was 452.76mg/kg,which was significantly lower than that of the soil soil 585.16mg/kg.Along the elevation of 175 m to 145 m,the content of soil TP in the WLFZ showed a decreasing trend,which may be related to the length of the flooding soil.The content of TP decreased with the depth increasing from 0cm to 20 cm,and the content of TP decreased with the depth of flooding.The possible sedimentation and pollutants could be related to the influence of ground runoff infiltration.The content of TP in the waterlogging zone decreased significantly after flooding,probably due to the migration of phosphorus to the overlying water in the flooded soil.The contents of inorganic phosphorus in soil and water were 426.03mg/kg,accounting for 76.78%~94.7% of TP,phosphorus in inorganic phosphorus and organic phosphorus Or-P were 82.05mg/kg,accounting for 5.3% 23.22%.The phosphorus forms extracted by CJ method included five kinds of Ex-P,Al-P,Fe-P,OP and Ca-P.The Ca-P content was 385.20mg/kg,accounting for 76.3~87.6% of TP,Phosphorus is mainly Ca-P.The contents of soil active phosphorus(BAP)in the WLFZ were 113.50mg/kg,including Ex-P,Al-P,Fe-P and Or-P,accounting for 8.5%~44.2% of TP.Migration occurs,so the falling water with a certain risk of phosphorus release.The content of Ca-P decreased with the increase of depth along the elevation from high to low.The effect of O-P and Ca-P on the release of Ex-P and Al-P in the soil was low.The correlation analysis showed that Ca-P was positively correlated with TP and IP in the Pengxi River the WLFZ,indicating that Ca-P was the main source of TP and IP,and the increase of TP and IP content mainly came from the increase of Ca-P The There was a significant positive correlation between BAP and Al-P and Or-P,indicating that Al-P and Or-P were the main sources of BAP,and the increase of BAP content mainly came from Al-P and Or-P.TN was positively correlated with Al-P and BAP.Due to the complex method of soil BAP and Al-P determination method,TN method was simple,indicating that there might be a way to express BAP value with TN.3)The adsorption of phosphorus to the soil in the WLFZ was fast adsorption at 0~2h,the adsorption was slowed up at 2~24h,and the adsorption equilibrium was reached at 24 h,which was the best with the quasi-second-order kinetic model,indicating that the soil adsorption rate And the secondary concentration of phosphorus concentration was linear.The maximum adsorption capacity of the soil was 137.79~603.92mg/kg,the mean value was 305.05mg/kg.The content of soil EPC was between 0.045 and 0.120mg/L,and the mean value was 0.069mg/L.The net phosphorus adsorption concentration of the soil was lower than that in the overlying water,indicating that the soil After the time of flooding,this time showing the adsorption of phosphorus state,in the absence of exogenous phosphorus inflow case,the performance of soil-water system of phosphorus "sink".