| At present,Beijing-Tianjin-Hebei region has been highly concerned with its serious air pollution led by PM2.5.As one of the important natural sources of particulate matter,soil erosion and dust emission by wind not only causes land degradation in the wind erosion area,but also leads to air pollution in the wind erosion area and its downwind area.Therefore,the study on the dust emission and transport characteristics of soil erosion by wind and its control measures over Beijing-Tianjin-Hebei region,could be of great significance for the prevention and control of wind erosion,dust emission and air pollution in the region.In the study,wind tunnel tests and field observation were used to explore the mechanism of dust emission by wind erosion in four typical surface types over Beijing-Tianjin-Hebei region,and validate the modified Wind Erosion Assessment Model(WEAM)in the study area.The modified WEAM was used to clarify the areas where soil wind erosion and dust emission take place,to study the emission and transport characteristics of PM2.5,PM10and dust caused by wind erosion,and explore the dust control by conservation tillage in Beijing-Tianjin-Hebei region,combined with the analysis of weather,soil and vegetation in the investigated area.The main results are as follows:(1)The vertical fluxes of PM2.5,PM10and dust in soils of bare land(BL)were higher than that in soils with flat residue(FR),maize standing stubble(MS)and a combination of maize standing and flat residue(SR),with a significance of 0.05.In wind tunnel tests,compared with bare land(BL),the vertical fluxes of PM2.5,PM10and dust of soils with FR,MS and SR decreased by 88.9±12.7%,54.3±40.0%,and 56.1±40.1%at different wind speeds,respectively.In the field,the vertical fluxes of PM2.5and PM10in soils of SR were the smallest,followed by that of MS and FR,and soils of BL had the largest vertical PM2.5and PM10fluxes.The results show that the modified WEAM had an acceptable agreement with the vertical PM2.5and PM10flux in soils of agricultural lands under four surface covering conditions in the field(as the model performance index d?0.84,and R2?0.88).The modified WEAM could adequately simulate the vertical PM10and dust flux for soils in four surface types and the vertical PM2.5flux in BL and MS in the wind tunnel(as d?0.98,and R2?0.88).(2)The threshold friction velocity of soil particles in the study area increased during January to August and then decreased during August to December,and increased from northwest to southeast in space.In the investigated area,15%of the total area was affected by wind erosion,36%of which was located in Zhangjiakou,32%in Chengde and 12%in Beijing,and others were mainly distributed in the coastal areas.The starting modulus of PM2.5,PM10and dust caused by wind erosion in Beijing-Tianjin-Hebei region from January to March was the largest,followed by October to December,April to June,and July to September.The starting modulus of PM2.5,PM10and dust caused by wind erosion in Beijing-Tianjin-Hebei region was the largest in high altitude zone(AL1:altitude>1000 m),followed by middle altitude zone(AL2:altitude>500?1000 m)and the low altitude zone(AL3:altitude<500 m).(3)During the year of 2017 to 2018,84.6%of the PM10caused by wind erosion in AL1 of Beijing Tianjin Hebei region was transported to the middle and low altitude zone by airflow.48.1%of the PM10caused by wind erosion in the AL2 was still in AL2,and 37.3%of that was transported to the AL3 by airflow.83.2%of the PM10caused by wind erosion in AL3 was still in AL3.The external concentration of PM2.5and PM10in AL3 in the study area from the wind-sandy region in northern China was the highest,followed by AL2,and AL1.Besides,there was a significant negative correlation between the external concentration of PM2.5and PM10and local wind speed(P<0.01).(4)The reduction of PM2.5,PM10and dust emission by maize standing stubble decreased first and then increased with the increase of stubble height,and that by maize flat residue cover increased with the increase of the coverage of maize flat residue.A combination of maize stubble and flat residue is needed to prevent vertical PM2.5,PM10,and dust flux at the wind speed of12?24 ms-1.Through conducting conservation tillage in Beijing-Tianjin-Hebei region,SR was proved to have the highest reduction rate for the regional dust emission(28.1%),followed by MS(26.5%)and FR(6.7%). |
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