Use Of Purple Soil Typical Small Watershed Non-point Source Phosphorus Output Model

The hilly areas of purple soil located in the central zone of upstream of Changjiang River, is a main part of agriculture in Sichuan province. In this zone, tremendous losses of water and soil, unreasonable agricultural cultivation and fertilizer management increasingly cause serious non-point pollution. Among these factors, the employment of excessive phosphorus is especially prominent. Non-point pollution not only causes soil degeneration and water quality decline, but also takes great pressure on the sustainable development of agricultural ecosystem of Changjiang valley.In this thesis, the migration rule of phosphorus sloping cropland of purple soil was studied by manual work and natural rainfall, and the runoff parameters of sloping cropland were estimated and calibrated by some models. Meanwhile, a typical agricultural ecosystem in the watershed was selected to study the non-point pollution of phosphorus, the route of pollution and the effect on water environment by monitoring the phosphorus transport in surface water and ground water, so that some scientific bases for preventing and controlling the export of non-point source pollutant from the hilly area of purple soil could be provided.The main conclusions have been drawn as follows.1. Rainfall intensity, sloping degree of cropland and crop coverage have effects on the runoff dynamics and export quantity of phosphorus. Under the same sloping degree, the crop coverage can increase the subsurface flow and decrease the overflow, but has little impact on runoff process. The crop coverage influences on phosphorus transport. However, rainfall intensity has little effect on phosphorus transport. Soil physical structure and crop characteristic are two dominant influencing factors on dissolved phosphorus (DP).2. Phosphorus of sloping cropland transported through overflow and subsurface runoff, the transported volume ascended as rain intensity strengthening. Under rain storm, the highest transported volume of phosphorus through cropland could reach 1.7 kg/hm~2, the phosphorus transport of cropland with coverage through subsurface runoff could reach 0.18 kg/hm~2.2. After more times of simulated rainfall, the forecast model of total phosphorus (TP) could be expressed as C_n = aQ~2 + bQ + c. The rainfall is a major influencing factor on model parameter b, and there is a prominent correlation between a and b.3. Surface runoff has mainly effect on the export concentration of TP in the watershed, and high export concentration of TP takes place in the seasons of big runoff. The correlative coefficient between export concentration of TP and runoff is 0.773, which reaches prominent correlation. Moreover, the correlative coefficient between export load of TP and runoff is 0.758, which also reaches prominent correlation.4. The residual rate of TP is mostly dependent on hydrophytes and microorganisms. The biological activity is stronger in spring and summer, so the residual rate of TP is highest. The maximum residual load of TP is 49 mg/m~2·d in autumn. The correlative coefficients between residual rate of TP and surface runoff and residual load are both over 0.7, which reaches prominent correlation.