| At present, the studies on nutrient loss of purple soil are almost in two ways, surface runoffand sediment, ignoring the influence of subsurface flow, which holds suitable share in thenutrient loss. In this study, by artificial rainfall experiment, we analyzed the characteristics ofnitrogen and phosphorus loss in three ways, namely surface runoff, subsurface flow andsediment. The impacts of slope degree and rainfall intensity on soil erosion and nutrient losswere investigated. The proportion of the loss of nitrogen and phosphorus with interflow, surfacerunoff and sediment were calculated, in order to provide scientific bases of the assessment,prediction, prevention and treatment of the purple soil erosion and nutrient loss. The main resultsare as follows:（1） Subsurface flow possess a peak pattern as the variation of slope degree and rainfallintensity. Under the same rainfall intensity and different slope degrees，peak values are on10°-15°; Under the same slope degree and different rainfall intensities，peak values are on1.6-2.12mm/min.（2） The cumulative sediment yield increases with the creasing of rainfall time, while the rateof increasing reduces gradually. Sediment loss is characterized by peak pattern during the rainfall,having positive correlation with slope degree，coming earlier when rainfall intensity. Sedimentyield increases with the increase of rainfall intensity, and this effect is more and more obviouswith the increase of slope degree. At the same slope degree, sediment transport rate and sedimentconcentration are increasing with the rainfall intensity increasing. （3） In the surface runoff, slope degree and rainfall intensity have little effect on nutrientconcentrations. Concentrations and loss of TN are negatively correlated with rainfall intensity.NO3-N concentrations are negatively correlated to slope degree, but the loss are positivelycorrelated to slope degree, and characterized by peak pattern with the increase of rainfallintensity. Concentrations and loss of TP are negatively correlated to rainfall intensity, but are notsignificant on the response of slope degree.In the subsurface flow, nitrogen concentrations are not significant on the response to slopedegree and rainfall intensity, nitrogen loss are characterized by peak pattern with the increase ofslope degree and rainfall intensity. Phosphorus concentrations are positively correlated to theslope degree, but the response of rainfall intensity is not significant. Phosphorus loss ischaracterized by peak pattern with the increase of slope degree and rainfall intensity, and has agreater impact by rainfall intensity than slope degree.In the sediment, nitrogen concentrations are negatively correlated with the slope degree andrainfall intensity, but their losses are positively correlated with slope degree and rainfall intensity.Phosphorus concentrations are negatively correlated with the slope degree, while the response ofrainfall intensity is not significant. Their losses are positively correlated to of slope degree andrainfall intensity. Enrichment of soil nutrients is affected by slope degree and rainfall intensity,and slope degree has a greater impact on the enrichment of nitrogen while rainfall intensity has agreater impact to enrichment of phosphorus.（4） TN、NH4-N and NO3-N concentrations are all higher in subsurface flow than in surfacerunoff. TN concentration ratios between subsurface flow and surface runoff are from7.61to60.30, with negative correlation with slope degree but positive correlation with rainfall intensity.NH4–N concentration ratios are characterized by peak pattern with the increase of slope degreeand rainfall intensity. NO3-N concentration ratios are negatively correlated with slope degree,and positively correlated with rainfall intensity. The subsurface flow is one of the main ways ofnitrogen loss. Phosphorus are mostly lost with sediment transport. |
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