Response Of Soil Erosion And Nutrients Losses To Individual Rainfall Under Different Land Uses At Karst Yellow Soil Slope

In order to understand the response of soil erosion and nutrients（nitrogen,phosphorus）losses to individual rainfall under different land uses at Karst yellow soil slope,water and sediment samples were collected from different runoff plots.These samples comprised conservation forest,farmland,natural meadow,bare land,and economic fruit forest land uses.The results indicated that:（1）The rainfall of rainy season at Karst yellow soil area（Yangjichong small watershed）belonged to light rainfall to heavy rainfall,and light rainfall to moderate rainfall accounted for the majority.The duration of rainfall was very short,and the rainfall process was relatively stable and concentrated.Soil erosion in this area was very easy to occur,traditional moderate rainfall and above rainfall were likely to be erosive rainfall.（2）The descending order of runoff per unit area of the five land-use types were as follows:bare land>natural meadow>farmland>conservation forest>economic fruit forest.The sediment yields per unit area were（in descending order）as follows:farmland>bare land>economic fruit forest>conservation forest>natural meadow.Among which,the runoff per unit area,sediment yields per unit area of farmland and bare land increased sharply under the influences of large rainfall and high intensity rainfall events.The runoff per unit area showed good cubic function relationships with maximum ten minutes rain intensity(I₁₀)and maximum thirty minutes rain intensity(I₃₀),and had good quadratic function relationships with maximum sixty minutes rain intensity(I₆₀)and the linear function relationships with average rainfall intensity（I_平）were better,respectively,and the same as sediments yields per unit area.（3）Farmland runoff(5.53 mg?L^-1<ρ（TN）<15.10 mg?L^-1),bare land runoff(2.37mg?L^-1<ρ（TN）<8.32 mg?L^-1)could lead to nitrogen loadings increasing in receiving waters,while that of conservation forest(1.37 mg?L^-1<ρ（TN）<2.73 mg?L^-1)and natural meadow runoff(1.13 mg?L^-1<ρ（TN）<2.14 mg?L^-1)had minor impacts on pollutant loadings in receiving waters.The total nitrogen（TN）losses of per unit area of 5 types of land uses in descending order were farmland>bare land>natural meadow>conservation forest>economic fruit forest.Among which,the total nitrogen（TN）losses of per unit area of farmland and bare land increased sharply under the influences of large rainfall and high intensity rainfall events.Farmland and bare land were dominated by particulate nitrogen（PN）,which accounted for 61%⁸7%and52%⁸1%of the losses of TN,respectively.Economic fruit forest,conservation forest,natural meadow were dominated by dissolved nitrogen（TDN）.Nitrate nitrogen（NO₃^--N）losses in TDN of five land uses had the highest proportion.The proportion of NO₃^--N to TN in descending order were natural meadow>conservation forest>economic fruit forest>bare land>farmland.The TN losses of per unit area with the intensity showed good cubic function relationships.（4）Farmland runoff(0.73 mg?L^-1<ρ（TP）<2.49 mg?L^-1),bare land runoff(0.10mg?L^-1<ρ（TP）<0.50 mg?L^-1)and economic fruit forest runoff(0.13 mg?L^-1<ρ（TP）<0.46 mg?L^-1)could lead to phosphorus loadings increasing in receiving waters,while that of natural meadow runoff(0.03 mg?L^-1<ρ（TP）<0.09 mg?L^-1)had minor impacts on pollutant loadings in receiving waters.The total phosphorus（TP）losses of per unit area of 5 types of land uses in descending order were farmland>bare land>economic fruit forest>conservation forest>natural meadow.Among which,the TP losses of per unit area of farmland and bare land increased sharply under the influences of large rainfall and high intensity rainfall events.Particulate phosphorus（PP）was the main loss of total phosphorus（TP）,ranging from 75.47%to 97.91%.The TP losses of per unit area with the intensity showed good cubic function relationships.The Soil erosion and nutrients losses correlated strongly with precipitation processes and land uses,suggesting that land-use structure optimization（graining for green,adjusting the vertical structure of vegetation and increasing vegetation coverage）and human disturbance reduction could be an effective method to mitigate soil erosion and non-point source pollution.