Study On Effect And Model Simulation Of Grassland On Suspended Substance And Phosphorus In Runoff

A series of environment problems occurred in the process of rapid urban development.The increase of impermeable pavements and the decrease of greenbelts result in runoff with a large amount of pollutants can't timely infiltrate in process of rainfall,and urban waterlogging and non-point pollution will happen.As an indispensable part of the urban ecological city system,greenbelts can not only retain runoff but also reduce pollutants in runoff.Suspended substance(SS)is a kind of pollutant in runoff,and it is also the carrier of other kinds of pollutants.Phosphorus(P)has become one of the key factors that lead to eutrophication,so it is necessary to prevent and control the pollution of SS and P in runoff.The common grasslands,sunken greenbelts and forest lands were selected as experimental objects.In this study,the effects of different experimental parameters on reduction of runoff SS and P were studied by field monitoring and artificial simulated rainfall experiments,and pollutants reduction models were obtained.The losses and reduction of SS and P in grassland(including tall fescue grassland,Bermuda grassland and bare land as a control)runoff in different inclinations(0°,5°,10°)and rainfall intensities(30,50,65,100mm/h)were studied by simulated rainfall.The results show that particulate P(PP)was the major component of P losses in bare land runoff,and dissolved P(DP)was the major component in grassland runoff.There were obvious linear relationships between losses of SS and TP as well as TP and PP in runoff.Rainfall intensity and inclination had significant effect on SS and P losses.Under the experiment conditions,the effect of rainfall intensity on reduction was greater than inclination.Grassland could effectively intercept runoff particles and therefore runoff pollutants reduction rate were over 86.04%for SS,over 91.97%for PP and 54.94%-89.82%for TP when compared with bare land.Also,the runoff SS and TP losses and reduction coefficient equations related to rainfall intensity,inclination,rainfall duration and total runoff were proposed to predict the losses and reduction of SS and P under different rainfall return periods.In sunken greenbelt,the reduction of SS and P in runoff was studied by controlling the parameters such as rainfall return period,temporal pattern of rainfall,height of the rainfall overflow inlet and vegetation type.The results show that runoff SS,TP,DP and DIP(dissolved inorganic phosphorus)amount reduction were 90.67%,86.82%,77.02%and 78.17%in experimental conditions,respectively.The reduction of runoff pollutants increased as the rainfall return period decreased and the height of rainfall overflow inlet increased.The sequence of SS reduction under different rainfall temporal pattern was type?>type?>type?>type?.S WMM model could be used to simulate the reduction of SS and P after parameter calibration,and the simulation error of TP was less than 5%.The concentration of SS and P in surface runoff of forest land was studied by monitoring natural rainfall.The results show that the concentration of SS was at low level and the dissloved P was the major component of P losses.SS and TP reduction coefficient in forest land runoff were over 0.90.The ability to reduce runoff pollutants was forest land>sunken greenbelt>common grassland.