Study On Removal Efficiency Of Agricultural Non-point Source Pollutants By Riparian Buffer Strips

China is a large agricultural country and agricultural non-point source pollution is serious harm to the water body.The work is necessary to prevent agricultural non-point source pollution.Riparian buffer strips traps the agricultural non-point source pollutants rely on soil and plant ecosystem,not only reduce the harm to water body,but also increase the green area,beautify the environment,and has a natural advantage.This paper carried out research utilizing riparian buffer strips to remove the main agricultural non-point source pollutants.Control factors of buffer strips to removel non-point source pollutants was importantly inspected,including plant type,slope and flow.And provide a reference basis for the construction of riparian buffer strips to control agricultural non-point source pollution.As a necessary condition of riparian buffer strips,the test soil and riparian buffer strips construction area soil should similar or close to the greatest extent simulate the environmental conditions of the study area.The experiment selects the soil which is close to the study area by controlling the soil mechanical composition,organic matter and pH indicators.Plant is one of the important controlling factors of riparian buffer strips,and the selection of riparian buffer strips plant is related to the effect of agricultural non-point source pollution prevention.The pot experiment planted four common plants: Trifolium repens,Black Taiwan,American holly and Bermudagrass,and they were used to observe the interception effect of different concentrations of sewage.By comparison,Trifolium repens integrated interception is the best for the seepage water,and the highest removal rates of COD,TP and TN were 25.3%,26.9% and 24.8%.So the follow-up riparian buffer strips simulation experiment selects the Trifolium repens.Other experimental conditions remain unchanged,respectively for 1%,3% and 5% gradient simulate experiment,it was found that seepage water pollutant removal rate is higher than the runoff water,and pollutant removal rate is decrease with the gradient increase.The removal rate of SS at the end of runoff water is 66.7% when the gradient is 1%,and the removal rate of COD,TN and TP at the end of seepage water is 62.7%,48.8% and 51.8%.By increasing the flow of riparian buffer strips,the riparian buffer strips for removal of pollutants decreased.When flow from 200L/s increased to 400L/s,the removal rate of SS at the runoff and TN,TP at the seepage decreased by 19.5%,16.7% and 16.4% at 1% gradient conditions.Each point of different depth along Riparian buffer strips,removal efficiency of pollutants are also different.With increasing depth,Removal efficiency increased significantly.When gradient of buffer strips is 1%,the depths of 0.4m is higher than 0.2m deep in the effluent TN、TP removal efficiencies,they were more than 12.1% and 13.8%.And Seepage water is much higher than the surface runoff water in removal efficiencies.In this study,method is curve fitting to determine the optimum width of riparian buffer strips.By fitting the experimental data,the best width is increasing as the gradient growth.When SS removal efficiency of runoff water was 80%,gradient of buffer strips is 1%,its best width is 12.2m,optimum width increase 16.7m when the gradien is 5%.When TN concentration of seepage water is Ⅳ grade water quality standards,best width of 1% gradient is 20.1m,optimum width increase 14.8m when the gradien is 5%.