| Non-point source pollution caused by soil and water loss has become the main factors influencing the water quality in the catchment area of middle route of south-to-north water diversion project(SNWDP).The Dan River,as an important source of the SNWDP,the water quality stability and improvement of it is critical to the benefit of the middle route of SNWDP.This thesis explored the transport rules of runoff,sediment,nitrogen(N)and phosphorus(P)at the spatial scale from slope to watershed scales in Yingwugou watershed.Simulated rainfall experiments on slope were carried out to analyze(1)Characteristics of runoff and sediment yield with different vegetation cover and cultivation measures and it's impacts on runoff,sediment and N&P loss from sloping field.(2)The runoff-sediment-nutrient transport processes were systematically analyzed with typical rainfall in the watershed.(3)The average annual amount of soil erosion was calculated based on the RUSLE model.(4)The spatial distribution characteristics of N and P in soil of Yingwugou Watershed,the soil erosion intensity and priority control area for "erosion-nutrient" with N and P was identified.(5)The export mechanism of soil N and P was revealed through runff-sediment-nutrient transport process with typical rainfall.The results were conductive to provide scientific reference for governance and control of soil erosion and non-point source pollution in water catchment areas.(1)By revealing the transport rule of runoff,sediment and nutrient under different vegetation and cultivation measures through simulated rainfall experiment on runoff plots,the response relationships among water-sediment-nutrient loss were clarified.Different vegetation and cultivation measures included peanut monoculture(PL),maize monoculture(CL),upper slope for bare land + lower slope for peanut monoculture(BP),corn interplanted peanuts(TCP),corn interplanted soybean(TCS),downslope tillage(BS),straw mulching(SC),and the bare land(BL)as a control.The results showed that surface runoff under different vegetation and cultivation measures are:BL>CL>SC>TCS>BS>BP>PL>TCP with the rainfall intensity 1.20 mm/min,60 min duration.The runoff amount with CL,SC,TCS,BS,BP,PL and TCP was 93%,75%,51%,39%,28%,12%and 6%of that with BL.And for sediment yield,it was shown as BL>BS>SC>CL>BP>TCS>PL>TCP.The sediment yield with BS,SC,CL,BP,TCS,PL,TCP is 87.4%9.3%7.1%,6.2%,3.3%,2.0,and 0.4%of that with BL,respectively.The vegetation measures and straw mulching showed better reduction effect on sediment than that on runoff.The N loss in the process of runoff and sediment yield was greater than P loss.Nitrate N was the main form for N loss in surface runoff which accounted for 48.4%-78.9%of total N loss,Total phosphorus consisted of 42.2%to 98.3%dissolved phosphorus.(2)The relationship between rainfall and runoff response of typical rainfall events was analyzed and the soil hydrological group parameters(soil saturated hydraulic conductivity,Ks)were determined by Vereecken transfer function model in the watershed.Using K-means clustering method to select precipitation(P),rainfall duration(D),the maximum rainfall intensity in 30 minutes(I30),154 rainfalls between 2011 and 2013 were divided into three types.Type ?(low P and short D)had the highest occurrence frequency,accounting for 67.6%of the total number of rainfall.Type ?(moderate P,moderate D and high I30)was less,accounting for 26.6%of the total number of rainfall.Type ? had the lowest frequency(high P and long D),accounting for 5.8%of the total number of rainfall.The maximum error of predicted soil saturated hydraulic conductivity of 0 to 10 cm in the surface layer forecasted by Vereecken transfer function model and measured values was within 25%,the spatial distribution of Ks at watershed scale could provide key hydrological parameters of soil for the application of hydrological models in Yingwugou watershed.(3)The spatial distribution characteristics of soil erosion intensity under different land use types were clarified in the watershed.The amount of soil erosion in Yingwugou watershed was 2247.2 t/a,the average annual soil erosion modulus was 1247.7 t/km.The soil erosion intensity in the study area was mainly slightly erosion.The slightly and light erosion area accounted for 81.8%of the basin area which distributed in the channel,flat area of the downstream,grass and forest land of the midstream and downstream.Intense and extreme intense erosion area accounts for 2.7%and 0.2%of the total study area which mainly distributed in the steep cultivated slope land in the midstream and steep slope land in left bank of the river.Yingwugou watershed was divided into six regions which named as Y1,Y2,Y3,Y4,Y5,and Y6.In Y1,farmland was the main land use which accounted for 25.1%of the total area and the amount of soil erosion accounted for 32.7%of that in the whole watershed.With the increase of the grassland and forest land,the soil erosion intensity reduced.Accounting for 49.7%of the total area,Y5 sub-catchment had 58.7%amount of soil erosion comparing with the total watershed.(4)According to the spatial distribution characteristics of the soil erosion and nutrient,the priority control area of "erosion and pollution" was identified.The average content of total N,ammonium N and nitrate N in soil was 0.87 g/kg,8.66 mg/kg and 2.73 mg/kg,respectively.The optimal model of the spatial distribution of soil total N was the Linear model,and for soil ammonium N and nitrate N were the Gaussian model.The average content of total soil P and available P in Yingwugou watershed was 0.65 g/kg and 8.70 mg/kg.The optimal model of the spatial distribution of them was the Exponential model and the Gaussian model.Kriging interpolation showed that it demonstrated patchy distribution where the soil N and P contents were high.The high value area for total soil N was mainly distributed in northwest forest land and slope farmland at two sides of middle section of river.For total soil P,the high value area was mainly distributed in the southeast and on both sides of the middle and lower reaches.Based on the established "soil N&P erosion modulus" index,the priority control can be accurately identified.(5)The export mechanisms and the spatial scale effects of N and P in typical rainfall-runoff process were revealed.With three typical rainfall events(E1,E2 and E3),the total N export in runoff were:24.2 kg,10.6 kg and 2.8 kg,of which the proportion of nitrate N to total N was 75.6%,69.6%and 70.1%,respectively.The export of the P in runoff amount is far less than that of N.The output of total P in surface runoff was 0.6 kg,0.1 kg,0.1 kg,of which the proportion of dissolved P to total P was 82.1%,76.5%,12.1%,respectively.Event mean concentration(EMC)and Event pollutant loads per unit area(EPL)of N and P showed a decreasing or stable trend with the area added from of Y1 to Y6.The land use had a significant effect on N and P export.To sum up,the configuration of vegetation type and pattern at slope scale and adjustment of land use at watershed scale could improve water quality by alleviating runoff and controlling sediment. |
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