Transport of phosphorus in runoff and sediment with surface runoff from bare purple soil during indoor simulated rainfall

Phosphorus(P)in surface runoff from purple soil is a critical element of agricultural nonpoint source pollution,leading to eutrophication of surface waters in the Three Gorges Reservoir Area(TGRA)of China.This work aimed to understand the processes and mechanisms of P losses from bare purple soil.Based on an indoor rainfall simulation experiment,we focused on the processes of surface runoff and P losses via different hydrological pathways.Experimental treatments included three simulated rainfall intensities,four slope gradients,and three fertilizer treatments.P loss from sediment was the main pathway in the purple soil,and bioavailable P was mainly transferred in dissolved P(DP)of runoff water.The P loss loads tend to grow with the increase of the slope until 25°for the maximum load of runoff water and 20°for the maximum load of sediment.Concentrations of DP in the surface runoff after fertilizer application can exceed the estimates of those required for accelerated eutrophication.Sediment P control might be an essential way for reducing P loss in purple soil for the local government and farmers of TGRA.