Study On Slope Runoff,Sediment And Rainwater Solutes In Shixia Watershed Of Miyun,Beijing

Miyun Reservoir Area is an important water source protection area in the capital.In view of the increasingly severe non-point source pollution risk in Miyun reservoir water source protection area,this paper integrated the location monitoring data of runoff plot in Shixia watershed of Miyun reservoir area from 2007 to 2016,and quantified the characteristics of rain peak morphology?peak width,peak number,peak value,peak position and continuity,etc.?in Miyun reservoir area in order to analyze the influence of rain peak morphology on runoff and sediment production process on slope surface,and discuss the influence of different vegetation cover types?Robinia pseudoacacia forest,Vitex negundo shrub and Zea mays field?on water quality change during rainfall redistribution through the research methods of field location monitoring,indoor analysis and numerical analysis.The research results can provide theoretical basis for controlling soil erosion and non-point source pollution on slope surface in Miyun water source protection area.The main conclusions are as follows:?1?The order of correlation between rain peak morphology indexes and runoff yield was peak width > peak number > peak value > multi-peak continuity > peak position.Among statistical rainfall characteristic index,I60 had better explanatory power on runoff and sediment yield.However,compared with the TPR,the explanatory power of I60 to runoff sediment was significantly lower.The peak rainfall amount of a rainfall?TPR?was a comprehensive index reflecting peak number,peak value and peak width,and had the highest correlation with the runoff and sediment yield.The prediction error of runoff yield model based on rain peak rainfall was about 20%,and the fitting degree was high?R2=0.82?.?2?With the increase of vegetation coverage,both the runoff and sediment yield showed a decreasing trend.When the vegetation coverage reached more than 60%,the runoff and sediment yield tended to be stable.There was no significant difference between the runoff and sediment yield of Robinia pseudoacacia forest,Vitex negundo Bush and grassland?P > 0.05?,which could be reduced by more than 93% and more than 99.8%,while the runoff and sediment yield of Zea mays were only 29.8% and 46.6%.?3?The influencing factors of runoff were rainfall > vegetation > topography > soil,and the average correlation ratio was 26.82%,25.39%,23.91% and 23.87%,respectively.The influencing factors of sediment were runoff > vegetation and rainfall > soil > topography.The average correlation ratio was 25%,20%,18% and 17%,respectively.The order of important factors affecting runoff was stable infiltration rate,I60 and litter thickness,with grey correlation degrees of 0.81,0.79 and 0.77 respectively.The order of important factors affecting sediment yield was litter thickness,runoff and steady infiltration rate,with grey correlation degrees of 0.84,0.82 and 0.80 respectively.There was interaction between vegetation,soil,topographic factors and rainfall intensity in the impact on runoff and sediment yield.Vegetation and soil had the best effect on runoff under reduced by low rainfall and heavy rainfall.Litter and soil permeability had the strongest effect on sediment reduction in general rainstorm.?4?The main cations in the rainfall were Na⁺,NH₄⁺,and Si,accounting for 80% of the total.The anions were mainly NO3-and Cl-,accounting for 94.6%.There was no significant difference in average cation content between Robinia pseudoacacia forest,Vitex negundo shrub and Zea mays field?P > 0.05?.The content of cation and anion in litter infiltration water of Robinia pseudoacacia forest was higher than that in shrub of Vitex negundo?P<0.05?.The cation and anion of soil infiltration water in corn field were significantly higher than those in Robinia pseudoacacia forest and Vitex negundo shrub,and there was no significant difference between the latter two?P>0.05?.?5?When rainwater passed through the canopy and litter layer,the organic matter content increased significantly.The increase through the canopy was 0.42-1.49 times,and the increase through the litter layer was 1.95-4.69 times.After rainwater passed through the soil layer of the forest,the organic matter was largely absorbed.The absorption rate of Vitex negundo shrub was 52%,Robinia pseudoacacia forest was 23%.The canopy,litter and soil layers of all vegetation which included Robinia pseudoacacia forest,Vitex negundo shrub and Zea mays field could absorb and release ions.Only the absorption of soil layer of Robinia pseudoacacia forest exceeded the release amount?5.67 times of the release amount?,with the strongest filtration capacity.?6?The contents of total phosphorus,total nitrogen and COD in surface runoff of different regions were all shown as follows: Robinia pseudoacacia forest > Vitex negundo shrub > grassland < Zea mays field < bare land.There was no significant difference in total phosphorus,total nitrogen and total COD between Zea mays field and bare land.