Study On Phosphorus Fractions And Transformation Characteristics Of The Soils From Water-Level-Fluctuating Zone In Pengxi River,Three Gorges Reservoir

As a transitional zone between terrestrial and aquatic ecosystems,the water-fluctuating zone（WLFZ）is an active site for the conversion of nutrients in ecosystems.After experiencing periodic flooding and drowning,the environmental conditions,physical-chemical properties of the soils from WLFZ are changed,which has an important impact on the phosphorus cycle of soils.Therefore,a comprehensive study on the transformation characteristics and the distribution of phosphorus forms of the soils with different altitudes,depths and periods from WLFZ,is of great significance for a deep understanding of the migration of soil phosphorus and the conversion of source and sink.The research object selected the soil from WLFZ in the Pengxi River.The chemical-physical properties of the soil from WLFZ were studied.The phosphorus forms of the soil from WLFZ in different altitudes,depths and periods were studied.The transformation characteristics of phosphorus forms of the soil from WLFZ of exogenous phosphorus were discussed,and the phosphorus release characteristics of the soil-water interface in WLFZ were studied by the film diffusion gradient（DGT）technique.The main results show:（1）The TP content of soil with different altitudes from WLFZ is 471.60⁷83.04mg/kg.The Bio-P content of the 175 m altitudes soil was significantly higher than that of the soil from WLFZ.There was no significant difference in Bio-P content of the soil from WLFZ,indicating that the soil was flooded and dried,and the soil bio-P is released into the overlying water body.The soil phosphorus content in different altitudes was significantly correlated with pH and Fe_ox content.The different altitudes soils have different flooding durations,which make the soil pH and Fe_ox content different,which affects the distribution of phosphorus forms in WLFZ.The average TP content in the surface soil of the fading zone was 667.39 mg/kg,which was higher than the average TP content of the lower soils of 602.85 mg/kg.The contents of Ex-P,Al-P and Fe-P in the surface soil of 0⁵ cm in WLFZ were significantly higher than those in the lower layer,and the phosphorus forms of the soil from WLFZ were characterized by surface enrichment.Phosphorus forms of soils with different depths were mainly correlated with particle size distribution,indicating that the particle size distribution mainly affected the soil phosphorus form in different depths,and the sediment deposition affected the soil particle size distribution in WLFZ.The Al-P and Fe-P content of the soil from WLFZ after flooding was significantly lower than that before flooding,indicating that the soil Al-P and Fe-P were released into the water body after the flooding.The content of phosphorus forms of soils with different periods from WLFZ was significantly correlated with the particle size distribution and OM content.The process of flooding and drying will change the physica-chemical properties of the soil from WLFZ,which will cause the difference of soil particle size distribution and OM content in the different periods from WLFZ,which will affect the distribution of phosphorus forms in different periods.（2）After adding exogenous phosphorus,the soils Olsen-P,Ex-P,Al-P and Fe-P reached the maximum on the first day.With the passage of time,the contents of soils Al-P and Fe-P decreased gradually,while the contents of Oc-P and Ca-P increased slowly.It indicates that exogenous phosphorus is added to the soil from WLFZ,preferentially converted into a highly active phosphorus form,and then converted to a stable phosphorus form.After 30 days,the slopes of the linear fitting equations of Ex-P,Al-P and Fe-P are small,while the slopes of the linear fitting equations of Oc-P and Ca-P are larger,indicating that exogenous phosphorus is added to the soil from WLFZ,the increase of Ex-P,Al-P and Fe-P is smaller,and the increase of Oc-P and Ca-P is larger.Over time,the exogenous phosphorus is mainly converted into stable phosphorus form of the soil from WLFZ.After air drying,the Olsen-P content of the soil from WLFZ increased significantly,and the Olsen-P content of the soil from WLFZ increased by 10.53¹72.93 mg/kg.At the same time,after air drying,the Ex-P,Al-P and Fe-P contents of the soil from WLFZ increased significantly,and the Oc-P content of the soil from WLFZ decreased significantly.Big.It is indicated that air drying treatment results in a more stable phosphorus form conversion to a more active phosphorus form.（3）The phosphorus maximum adsorption amount Q_max of the surface soil from WLFZ is larger than the maximum adsorption amount Q_max of the middle and lower layer.The Q_max of the soil from WLFZ was positively correlated with the clay fraction and Fe_ox content,indicating that the soil particle size and Fe_ox content in WLFZ played an important role in the adsorption capacity of phosphorus.The DGT-P and DGT-Fe²⁺concentration of the soil profile from WLFZ were 0.007⁰.198 mg/L and 0.014¹.915mg/L,respectively.There is a positive correlation between DGT-P and DGT-Fe²⁺,indicating that there is a significant coupling relationship between DGT-P and DGT-Fe²⁺of the soil.The phosphorus diffusion flux F_d at the soil-water interface from WLFZ is0.0276⁰.0821 mg/（m²·d）,indicating that the phosphorus of the soil from WLFZ is released into the water body,which expressed as the phosphorus source.