Effect Of Acid Rain On The Structural Properties And Water Movement Characteristics Of Red Soil In Hunan

With the development of the industrial revolution and accelerated urbanization,the concentration of nitrogen oxides(NOx),sulfur oxides(SOx)and other harmful gases in the air has increased significantly,leading to an increase in the frequency of acid rain,thus acid rain as a global environmental problem has become a widespread concern.China is the third largest acid rain zone in the world after Europe and North America.The Red Loam Zone in southern China is one of the major acid rain zones in China and the world.The acidification of soils after acid rain causes environmental pollution and damage by altering the structural properties of the soil and the movement of water.In this paper,the effects of rainfall acidification(sulphuric acid rain at pH=1,2,3,4 and 5,and rain at pH=7),acid rain frequency and intensity(1 day/1 heavy rain of 20 mm intensity,2 days/1 heavy rain of 40 mm intensity,5 days/1 heavy rain of 100 mm intensity,all of which are sulphuric acid rain at pH=2),acid rain type(pH all of which are 2,and the molar ratio M of[SO42-]and[NO3-]in acid rain is 1:0,3:1,1:1,1:3 and 0:1,respectively)on the red soil tolerance,pore structure,aggregate stability,soil particle composition,surface infiltration capacity and non-uniform characteristics of water movement in Hunan Province were investigated by conducting a spray test on soil columns with acid rain as the main research object.The results show:(1)The strong acidic(pH<3)acid rain damaged the soil agglomerate structure,leading to a decrease in soil porosity,especially the non-capillary porosity,and an increase in soil weight,while the weak acidic(pH=4;pH=5)acid rain was conducive to enhancing the stability of the soil agglomerates,thus increasing the soil porosity,especially the capillary porosity,and decreasing the soil weight,suggesting that the destructive effect of the strong acid on red soil was significantly greater than the weak acid.However,under weakly acidic(pH=4;pH=5)rainfall conditions,soil dispersion of mucilage and fine powder particles along the interior of the soil non-capillary pores increased,resulting in coarsening of soil texture.As the better soil agglomerate and pore structure under weak acid(pH=4;pH=5)rainfall conditions increases the rainfall infiltration rate and reduces the non-uniformity of the infiltration water movement,weak acid will reduce the water-holding capacity of red soil compared to strong acid,which will reduce the drought resistance of red soil and make it more prone to soil erosion in the area,so the prevention and control measures should be strengthened for weak acid areas.(2)Under the conditions of the same total rainfall and acid rain pH,high frequency(once a day)and low intensity(20 mm/day)rainfall promoted the swelling of soil mucilage and the dispersion and fragmentation of soil aggregates,resulting in the reduction of soil porosity,especially the non-capsular porosity,and the increase of weight;while low frequency(once in 5 days)and high intensity(100 mm/day)rainfall increased the loss of soil dispersion mucilage and fine particles along the interior of soil non-capsular porosity,resulting in the coarsening of soil texture,indicating that high frequency and low intensity rainfall had a greater destructive effect on red soil.Due to the low frequency,high intensity acid rain conditions under better soil agglomerate structure and pore structure,increased the rainfall infiltration rate and reduced the non-uniformity of the infiltration water movement,under such conditions the surface is more likely to form runoff,and high frequency,low intensity rainfall compared with the soil is more lax,so it is more likely to cause large-scale soil erosion,so it should be strengthened for low frequency,high intensity acid rain areas of soil control and soil conservation.(3)Under the same pH conditions,sulfuric acid rain has a stronger destructive effect on soil colloidal material than nitric acid rain,aggravating the dispersion fragmentation of soil aggregates,soil porosity,especially non-capillary porosity,and weight increase.However,under nitric acid rain conditions,the internal loss of dispersed mucilage and fine particles in the soil is greater,the soil texture coarsening is more obvious;at the same time,due to the better soil agglomerate structure and pore structure under nitric acid rain conditions,increased the rainfall infiltration rate and reduced the non-uniformity of the infiltration water movement,so there is a greater need to strengthen the soil control of nitric acid rain zones.