Analysis On The Characteristics Of Runoff And Sediment And Non-point Source Pollution In The Bank Zone Of Miyun Resevoir

Miyun Reservoir is an important surface water source in Beijing.It plays a key role in the economic development of the capital.With the rise of Miyun reservoir water level and the construction of the reservoir and coastal zone,a series of changes have taken place in its ecological environment.In this study,12 sets of field standard runoff plots with different vegetation arrangements were set up to analyze the characteristics of runoff and sediment production under artificial and natural rainfall conditions,and five non-point source pollution indicators for Total Nitrogen(TN),Total Phosphorus(TP),Ammonia nitrogen(NH4+-N),Chemical Oxygen Demand(COD)and Biochemical Oxygen Demand(BOD5)were carried out,with a view to provide reference data for the construction of the field runoff plots.The results of the study show that:(1)There is a positive correlation between the diversity of vegetation distribution and the runoff reduction effect fr as well as the sand reduction effect fs Under natural rainfall conditions,the flow reduction effect of Salix babylonica+Syzygium aromaticum+Artemisia carvifolia is best in the mixed area of tree,shrub and grass,and the average flow reduction effect fr is 62.9%.The best sand reduction effect is Populus tomentosa+Syringa oblata Lindl+Humulus scandens(Lour.)Merr,and the sand reduction effect fs is 78.18%.The flow reduction effect under pure vegetation is:Populus tomentosa>Medicago sativa>Pinus tabulaeformis.The sand reduction effect under pure vegetation is:Populus tomentosa>Pinus tabulaeformis>Medicago sativa.The best mode for reducing flow and sediment in dual-vegetation configuration is Ailanthus altissima+Robinia pseudoacacia.Compared with the pure Pinus tabuaeformis,the Pinus tabulaeformis plus other vegetation mixed plots have a significant increase in flow reduction and sediment.The flow reduction effect under mixed plots of Pinus tabulaeformis and Ulmus pumila'Jinye,Fraxinus chinensis Roxb,Ailanthus altissima,and Populus tomentosa was increased by 20.46%.14.91%,20.17%,and 20.8%,respectively,compared with the pure Pinus tabulaeformis plot,and the sand-reducing effect was increased by 11.56%,6.97%,and 6.0%.1 1.91%.Of which.Populus tomentosa,Ulmus pumila'Jinye' and Pinus tabulaeformis had the best mixed effects,and the two vegetation in the mixed process with the Pinus tabulaeformis had a similar effect of reducing flow and sediment.(2)Runoff and sediment production under artificial rainfall is characterized by a significant change in rainfall time.Runoff plots basically have an increase in flow production with time and then become stable.The amount of sediment production increases steadily with time and then decreases steadily.Under 30 mm/h rainfall.the increase in flow production continued about 8-10 min,and the sediment production amount began to decrease in 6-8 min.Under the conditions of 60 mm/h rainfall.the increase in both flow and sediment production were completed in 10-12 min.The increase of rainfall intensity resulted in an increase in the increment stage of flow production and sediment production with a significant increase in the growth rate.However,the characteristics of the runoff of Populus tomentosa+Syringa oblata Lindl+Humulus scandens(Lour:)Merr did not change significantly with time.The flow production decreased with time,and the production of sediments decreased after a fluctuation.Taking into account the runoff coefficient and the rate of sediment reduction,the water conservation benefits of the vegetation configuration of Populus tomentosa+Ulmus pumila'Jinye'+Pinus tabulaeformis are the best.while the efficiency of the pure Medicago saliva is the worst.(3)Vegetation has a significant control effect on non-point source pollution,and the diversity of vegetation configuration is positively related to the reduction effect.Among the different vegetation allocations and horizontal control of wasteland,Populus tonmentosa+Syringa oblata Lindl+Hunulus scandens(Lour.)Merr had the best control effect.with the nutrient loss reduction rates of TN,TP.NH4+-N.COD and BOD5 between 77.76%and 92.24%.while Medicago sativa had the worst reduction rate of 28.09%-67.07%.Under dual-vegetation configuration type,Ailanthus altissinza+Robinia pseudoacacia plots had the best effect of pollution control.Under Pinus tabulaeformis and other vegetation mixed configuration,Populus tomentosa is optimal.(4)Under three natural rainfall conditions,the five non-point source pollution indicators showed a declining trend in the longitudinal comparison of the control of the reduction of surface source pollution over time and rainfall conditions.For the TP reduction control,the Pinus tabulaeformis+Ailanthus oltissima combination is the best.while for the remaining four indicators,the reduction ratio is the highest with the Pinus tabulaeformis+Ulmus pumila'Jinye',which shows that this vegetation configuration model has the best long-term benefits of non-point source pollution control.