Effects of Gradients and Rainfall Intensities on Phosphorus Loss Under Simulated Rainfall

Bio-available phosphorus (BAP) is a new criterion for evaluating water quality, so controlling BAP export has significant meaning for non-point pollution. Phosphorus- transporting dynamics under three gradients and rainfall intensities were simulated. The study showed that BAP increased with rainfall intensity and gradient increasing. Sediment extractable bio-available phosphorus (BPP) concentrations of overland flow were between 0.065~0.115 mg/L. Crop coverage could reduce the fluctuation of overland flow and subsurface runoff, and subsurface runoff could decrease the flux and BAP export through overland flow. BPP was absorbed by sediment and BPP of subsurface runoff was mainly through sediment transportation. Relationship between BAP concentration(y) and flux(x) could be expressed by: y=0.0144Ln(x) + 0.0074 (r² = 0.9014). The maximum BAP loss rate of sloping cropland of purple soil reached 0.296 g/hm² and the maximum soil loss rate reached 4461.89 kg/hm². Therefore, it is very important to evaluate the eutrophication of local water environment and analyze the overall effect of subsurface runoff.