Study On The Removal Efficiency Of Contaminants From Paddy Field Runoff By Sward Buffer Zone And Its Appropriate Width

Agricultural non-point source pollution is an important source for the water deterioration in lakes and rivers.Its prevention and control is a long-term task that needs to have adhered to.The southern region is characterized by abundant rainfall and highly overlapping rice seasons in the rainy season,so the pollution of paddy field runoff cannot be ignored.It has been demonstrated that the sward buffer zone is an effective method for controlling non-point source pollution.This experiment selected widespread bermudagrass(Cynodon dactylon(l.)Pers.)to build sward buffer zones.They were conducted outdoor to simulate runoff experiments.Based on outdoor experiments and laboratory analysis,the intercept effect of the sward buffer zone on nitrogen and phosphorus pollution from runoff was studied.Given runoff volume,velocity,inflow pollutants concentration,and width,the purification effect of non-point source pollution was explored.The main conclusions are as follows:(1)A large runoff test field was built in the sod buffer zone to analyze the changes of runoff concentration of nitrogen,phosphorus,and other pollutants in the sod buffer zone by runoff rate,runoff speed,and inflow pollutant concentration,and to explore the appropriate width.In the runoff experiment,under the conditions of large runoff,low runoff speed,and low pollutant concentration,the interception rates of TN,TP,ammonia nitrogen,nitrate-nitrogen,and DTP were 42.79%-74.66%,8.70%38.40%,49.73-88.51%,27.98%-49.07%,and 10.68%-48.05%respectively.There was a positive correlation between the runoff rate and the interception rate of nitrogen and phosphate,and a negative correlation between runoff rate and pollutant concentration.There is a significant logarithmic correlation between the interception rate and the width under different inflow conditions.A 25 m wide sward buffer can achieve a TN interception rate of more than 50%.The inflow condition has a fair influence on the TP interception rate that is between 10%and 40%.According to the fitting judgment of the appropriate width,the 25 m wide sward buffer zone can achieve better nitrogen and phosphorus interception effect.(2)The effect of the above influencing factors on the concentration of pollutants in the seepage was analyzed simultaneously,and the transport mechanism was discussed.The interception rate of pollutants in seepage was slightly higher than that in the runoff.Under the conditions of larger runoff,lower runoff velocity,and lower pollutant concentration,the interception rate of TN and TP in the superficial layer are 50.94%-70.86%and 21.12%-37.99%respectively.The interception rate of TN and TP in deep one is 55.45%-87.27%and 12.24%51.53%.(3)With the increase of the number of experiments,the interception ratio of nitrogen and phosphorus in the shorter width of sward buffer zone showed a trend of first increase and then decrease,and at the same time,it migrated along the direction of width increase.A shorter sward buffer zone in response to highfrequency rainfall-runoff pollution has the risk of phosphorus leaching.(4)According to the multivariate variance analysis of the factors affecting the removal,the inflow conditions and the width have significant effects on the retention of runoff pollutants by the sward buffer,and there are interactions between them.The influence of runoff,concentration,and width of pollutant inflow on the removal effect of pollutant seepage is significant.