| By collecting soil,water and sediment samples from the agricultural area in Wangbeng Region of Huaihe River Basin,the abundance,particle size,shape,color,composition and surface morphology of microplastics in soil at different soil depths,river surface water and sediment at different main streams and tributaries,and ditch surface water and sediment near different land use types were analyzed.The vertical and horizontal migration characteristics of microplastics in soil,rivers and ditches and related influencing factors were discussed.And the variation of microplastics loss and loss concentration with runoff in agricultural soil under different rainfall intensities and different slopes was studied by indoor simulation experiments,and the distribution of residual microplastics in soil after rainfall stopped.The effects of rainfall intensity and slope on the vertical and horizontal migration of microplastics in agricultural soil and the migration law of microplastics from soil to water with runoff were analyzed and explored.The main conclusions are as follows:（1）The average abundance of microplastics in soil ranged from 706 to 7611.67pieces/kg,the abundance of microplastics in agricultural soil is higher.The average abundance of microplastics in upstream<midstream<downstream,the abundance of microplastics in different soil layers is 0-5cm>5-10cm>10-15cm>15-20cm>20-25cm>25-30cm,mostly concentrated in 0-15cm soil layer.The soil conductivity and NH4+-N concentration are in the order of upstream>downstream>midstream,and the water content,TN concentration,NO3--N concentration,TP concentration and TDP concentration are in the order of downstream>midstream>upstream and the water content,TN and TP concentrations decreased with the increase of soil depth.The abundance of soil microplastics is highly significantly positively correlated with water content,TN,NO3--N,TP and TDP,and negatively correlated with p H and electrical conductivity.（2）The abundance of surface water in rivers and ditches ranges from 66000 to156200 pieces/m3 and from 16800 to 52400 pieces/m3,and the sediment abundance ranges from 860 to 13640 pieces/kg and from 2000 to 4560 pieces/kg,respectively.The abundance of microplastics in water is shown as rivers>ditches,and sediments>surface water;the abundance of microplastics in surface water showed primary tributaries> mainstream>secondary tributaries,and cultivated land>construction land>forest land;the abundance of microplastics in sediments showed mainstream>primary tribu-taries>secondary tributaries,and construction land>cultivated land>forest land.There is certain pollution in the water body at each sampling point of rivers and ditches.There is a significant negative correlation between the abundance of microplastics in river sediments and COD,and a significant positive correlation between the abundance of microplastics and TN and TDN,while there is no significant correlation between the abundance of microplastics in river surface water,ditch surface water and ditch sediment and water quality index.（3）The particle size of microplastics in the study area is divided into 20-150μm,150-300μm,300-500μm,500-750μm and>750μm,and the proportion of microplastics with small particle size is dominant,and the deeper the soil layer,the larger the proportion of microplastics with small particle size.There are three kinds of shapes:fiber,film and fragment,fiber is the most.Color is divided into transparent,black,brown,yellow,red,green,blue and purple eight colors,transparent color as the dominant color.The microplastics are mostly composed of PP,PE and PP-PE copolymer,with a small amount of Polyester,PA and ALK,and SEM analysis shows that microplastics have different degrees of degradation and weathering in the natural environment.（4）Under different rainfall intensities and slopes,the total loss of microplastics in agricultural soil is shown as surface runoff>10cm interflow>20cm interflow>30cm interflow.The increase of rainfall intensity and slope will increase the loss of microplastics and is conducive to the vertical migration of microplastics.The longer the rainfall time is,the more the amount of microplastics migrate downward.In terms of loss concentration,when the rainfall intensity is large,the loss concentration is mainly concentrated in the deep soil,and the longer the rainfall time,the greater the loss concentration in the deep soil.The greater the slope,the smaller the microplastic loss concentration in each soil layer.The average loss concentration of microplastics in shallow soil is greatly affected by rainfall intensity,and the average loss concentration of microplastics in each soil layer decreased with the increase of slope.For different soil layers,the microplastic loss and loss concentration are significantly and highly significantly correlated with the runoff yield and sediment yield of each soil layer,indicating that they are closely related to soil depth,runoff yield and sediment yield.As a whole,microplastic loss and loss concentration are significantly correlated with rainfall intensity,runoff yield and sediment yield in the rainfall experiment group.In the slope experimental group,70%of the factors are significantly correlated with slope,runoff yield and sediment yield.（5）The concentration of microplastics in surface soil is lower than that in deep soil under different rainfall intensities and slopes.The higher rainfall intensity will promote the movement of microplastics from higher end to lower end.The greater the slope,the higher the microplastics concentration in the deeper soil and the lower end of the soil,and the faster the microplastics migration from the higher end to the lower end,which may indicate that the microplastics will occur vertical migration under the effect of gravity or runoff.For each soil layer,the average concentration of microplastics in layer A（0-10cm）is 0°>5°>8°,and that in layer B（10-20cm）and C（20-30cm）is 8°>5°>0°,indicating that increasing slope is conducive to promoting downward migration of microplastics.Figure[87]table[8]reference[121]... |
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