Simulation Of Phosphorus Loss On The Weathered Granite Slopes With Different Erosion Intensities

Loss of phosphorus(P)carried with runoff and sediment during soil erosion is one of the main causes of agricultural non-point source pollution in water bodies,which currently becomes the main ecological and environmental problems.Weathered granite parent material soil is widely distributed in zhejiang-fujian hilly region with large surface undulations.Perennial high temperature and heavy rain and environmental problems such as water and soil loss and soil erosion often occur in the summer.At present,there are few studies on the characteristics of P loss in soil and water loss on such slopes,and the result series are incomplete.In view of this,this study used the weathered granite parent material soil as the research object to simulate the characteristics and processes of soil erosion and P loss on the slopes of different erosive intensities.A total of 30 effective artificial simulated rainfall experiments were conducted to systematically studied the characteristics of P loss from the weathered granite parent material soil slopes.In this study,two group soils were selected from two exposed layers of weathered granite parent material soil with different erosive intensities(red soil layer and sandy soil layer).The rainfall intensity(30 mm/h,60 mm/h,90 mm/h,120 mm/h,150 mm/h)and slope gradient(8°,15°,25°)were selected as variable factors and the method of artificial simulated rainfall test was adopted to explore the characteristics of P loss with runoff and erosive sediment.The main conclusions were as follows:(1)The P loss concentration in surface flow(0-8 mg/L)was much larger than that in the interflow(0-0.8 mg/L).As a whole,the P loss concentration in runoff increased with the increasing rainfall intensity.The P loss concentration in surface flow was less affected by the slope gradient while the P loss concentration showed different changing trends under different slope gradients in the interflow.Overall,the P loss concentration in interflow of sandy soil layer(0-0.8 mg/L)was greater than that of red soil layer(0～0.12 mg/L).(2)As a whole,the P loss amount in runoff increased with the increasing rainfall intensity,but it increased firstly and then decreased with the increasing rainfall intensity in the interflow of red soil layer.The P loss amount decreased with the increasing slope gradient in surface flow,but it was the largest on the 15° slope in the interflow of sandy soil layer while it increased slightly with the increasing slope gradient in the interflow of red soil layer.The P loss amount in the surface flow of red soil layer(2.05～562.73 mg)was greater than that of the sandy soil layer(0.21～364.42 mg)while it was opposite in the interflow,which were respectively 0.19～6.86 mg and 1.11-38.07 mg.(3)The sediment yield increased significantly with the increasing rainfall intensity or slope gradient.The sediment yield of sandy soil layer(4.11～4100.00 g)was much smaller than that of red soil layer(16.36～7448.00 g).The P content in the eroded sediment of sandy soil layer(1.02～3.92 g/kg)was greater than that of red soil layer(1.24～2.40 g/kg).The relationship of the effect on sediment carrying P loss amount was sediment yield>rainfall intensity>surface flow volume,and the slope gradient had little effect.(4)The P loss was mainly caused by sediment transport followed by surface flow and the least contribution to P loss was interflow.Rainfall intensity and soil properties were the key factors affecting the particulate phosphorus(PP)release by raindrop splashing in the surface flow.The main loss form of P in sandy soil layer was obviously affected by the rainfall intensity,which was dissolved phosphorus(DP)in gentle rainfall and PP in middle and heavy rainfall in surface flow.The main loss form of P in red soil layer was DP and was not obviously affected by rainfall intensity.DP was also the main P loss form in interflow,which was less affected by rainfall intensity and soil properties.(5)Rainfall intensity,the volume of surface flow and sediment yield were the main factors affecting P loss on slopes.In addition,the runoff and sediment yield as well as the P loss amount were significantly affected by rainfall intensity.At different experimental soil conditions,the volume of interflow was different due to the difference of soil infiltration capacity and thus the degree of impact on P loss was different.The impact of slope gradient on P loss was small or not obvious.To sum up,the phosphorus loss can be controlled by means of flow and sediment reduction in sloping land.