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 non-point 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.