| Phosphorus is the major limiting factor for eutrophication. As an important source, non-point source phosphorus pollution results in eutrophication seriously. Soil is the source of non-point source pollutants. Mobilization describes the initial separation of phosphorus pollutants from their source. And then, phosphorus begins to transfer. Understanding the mobilization mechanism is critical in controlling the phosphorus entering the water body effectively, mitigating and preventing eutrophication. The two primary processes of mobilization are soil phosphorus adsorption - desorption and soil erosion, which belong to solubilisation and detachment mobilization respectively. The features of soil phosphorus mobilization and soil erosion were studied by laboratory simulation and field monitoring at plot scale. The main conclusions are the following:1. Soil phosphorus adsorption process as follows: adsorption amount increased with time; adsorption rates increased highly at the beginning, and then decreased; the maximum rate presented the first hour. The dynamic curves of phosphorus adsorption can be best described with the two-constant equation. High phosphorus soil (TP 0.944-1.240 mg·kg-1) occurred desorption all the time within the range of adsorption concentration. The adsorption amount of low phosphorus soil (TP 0.337-0.588 mg·kg-1) increased with increasing equilibrium concentration of solution. The phosphorus adsorption isotherms were fit in well with Langmuir, Freundlich and the linear isotherm equation.2. Soil phosphorus absorption capacities were varied with different land use. The phosphorus absorption capacities of riverbed soil was thehighest, grassland slope soil was the lowest. The main factors influencing the soil phosphorus absorption capacity were Clay, Fe-P, Al-P, CaCO3 and Available Phosphorus (A.P.). There was a highly risk of phosphorus loss after rainfall from grassland slope, woodland slope, corn slope, corn farm, woodland and apricot orchard. 3. The phosphorus release processes of high phosphorus soil occurred desorption all the time, which could be fit in well with by the dynamic equation. The phosphorus release processes of high phosphorus soil took on an adsorption - desorption alternate dynamic process, which could not be fit in well with by the dynamic equation. The soil phosphorus and clay content and water-soil ratio conditions can affect desorption amount. The higher soil phosphorus and clay content, the higher desorption amount. The higher water-soil ratio, the lower desorption amount. With an increase in phosphorus solution concentration, soil phosphorus desorption capacity after adsorption decreased gradually.4. There was soil coarsening on each underside slope.. For the higher gradient slope soil without vegetation cover, the content of clay and silt before the rainy season was higher than those during the rainy season, and after the rainy season; the content of sand after the rainy season was higher than those during the rainy season, and before the rainy season. There was more highly soil coarsening on the upside slope than the middle part and underside slope. For the lower gradient slope soil within vegetation cover, there was not soil coarsening on the underside slope. On the underside slope, the content of clay and silt after the rainy season was higher than those during the rainy season, and before the rainy season; the content of sand before the rainy season was higher than those during the rainy season, and after the rainy season. There was soil coarsening a little on the upside slope.5. With the increase in precipitation, the content of clay in sediment was decreasing, but the content of sand was increasing. Rainfall, slope gradient, slope length and vegetation cover impacted sediment mobilization.
|
PDF Full Text Request