Effect Of Microplastics On Soil Hydraulic Parameters

Microplastics exist widely in the soil environment,and the microplastics in soil are mainly harmful to the physical and chemical properties of soil,as well as animals,crops and microorganisms in the soil environment.The presence of microplastics in soil will affect the pore structure of soil and change the water retention capacity of soil.In this study,the effects of different materials(PVC,PE),particle size(150um,550 um,950um)and abundance(0%,0.5%,1.0%,2.0% of dry weight of soil samples)on soil saturated water content,capillary water retention,field water retention and other hydrostatic parameters were studied by indoor simulation.The response of hydrodynamic parameters such as saturated conductivity and diffusivity to the abundance and particle size of PVC microplastics was clarified.The influence of PVC microplastics with different characteristics on soil water characteristic curve was explored by using pressure film instrument.Meanwhile,the applicability of PVC microplastics to VG model,BC model and other soil water characteristic curve models was illustrated by RETC software.The main conclusions are as follows:(1)Through the experimental research and analysis of PVC microplastics on soil hydrostatic parameters,it can be concluded that the presence of PVC microplastics with different particle sizes and abundance in soil will lead to a downward trend in the values of soil hydrostatic parameters.Under the condition of large particle size of microplastics,the soil saturated water content varied greatly with the change of abundance.When the microplastics particle size was 950 um,the abundance decreased significantly from 0.5% to 2%,decreasing1.07% and 4.72%.With the increase of microplastic abundance,the water holdup of soil capillary decreased.Compared with the saturated water content and capillary water holding rate,the water holding rate in the field decreased more obviously with the change of microplastic particle size and abundance.When the microplastic particle size increased from 0.5% to 2%under 150 um and 550 um conditions,the water holding rate in the field decreased by 1.59% and17.44%,respectively.4.34%,5.58%;Under the condition of the same microplastic particle size,increasing the microplastic abundance had the same effect on soil total porosity and capillary porosity.(2)The presence of PE microplastics with different particle sizes and abundance in soil would lead to a downward trend in soil hydrostatic parameters.But on the whole,the variation of PE microplastics abundance can have more influence on soil hydrostatic parameters.The presence of PP microplastics in soil has little effect on soil hydrostatic parameters.The correlation showed that when the microplastic type was PVC and the particle size was unchanged,the change of the abundance caused the obvious change of the water holding rate and the total porosity in the field.When the microplastic type was PE and the particle size was constant,the change of the abundance of the microplastic resulted in the obvious change of the water holdup and non-capillary porosity in the field.The microplastic type was PP,and under the condition of constant particle size,the change of the abundance caused the obvious change of the water holding rate in the field.(3)The presence of PVC microplastics with different particle size and abundance in soil will affect soil water conductivity.When the particle size increased from 150 um to 950 um,the saturated water conductivity of soil decreased by 14.57% and 6.49%,respectively,under the conditions of three kinds of microplastics abundance.9.87%,6.70%;10.93%,6.73%.To a certain extent,the change of microplastic particle size can affect the saturated water conductivity of soil.The presence of PVC microplastics in soil changed the horizontal diffusion rate of soil.With the increase of soil moisture content in each group,the horizontal diffusion rate parameter λ value showed a decreasing trend.(4)As the particle size of PVC microplastics in soil increased from 150 um to 950 um and the abundance increased from 0.5% to 2%,the water retention capacity of soil decreased.When the particle size increased from 150 um to 950 um when the abundance of microplastics was 2.0%,the soil moisture content decreased most obviously.When the particle size of microplastics increased from 150 um to 950 um and the abundance increased from 0.5% to 2%,the proportion of small and medium pores in soil decreased while the proportion of large pores increased.VG model can better express the soil moisture characteristic curve of simulated PVC microplastics in soil.This thesis through to carry out the micro plastic research on the influence law of the soil hydraulic characteristics and explore its effect mechanism,can make up the different characteristics of the micro plastic occurrence mechanism of the effect on soil hydraulic characteristics research,can provide better micro plastic occurrence under the condition of laying a foundation for the efficient utilization of soil resources,can also be used for domestic large irrigation area planted in micro plastic laminating north management to provide the reference.