| Soil erosion is an important cause of global soil degradation,an important research direction for soil and water conservation,and an environmental problem that is common to all parts of the world.Soil erosion not only takes away the nutrients in the soil,but also reduces the soil fertility.It also takes the sediment from the topsoil into the river channel and increases the amount of sediment transported by the river,causing the river to block and even raise the riverbed to cause flooding.The lost sediment carries Contaminants,that cause damage to the ecological environment in other places.As a carrier of soil nutrients and soil pollutants,soil humus is lost and migrated under the action of hydraulic erosion.On the one hand,it causes the soil nutrient content to decrease,on the other hand,it causes the pollutants to migrate and destroy the environment.Humus is an important part of soil organic matter.It consists of three major components: hydrophobic organic humic acid(HA),hydrophilic organic matter fulvic acid(FA)and water-insoluble humin(HM).Humic acid and fulvic acid are combined.Also known as humic acid,it is able to adsorb organic pollutants in the soil and is a source of soil fertility.Soil erosion leads to the loss of humic acid in the soil and is also an important research direction for soil degradation.As a severely eroded area,the Longchuanjiang Basin has a high degree of soil erosion and a serious decline in soil fertility.Studying the influencing factors of humic acid loss in the Longchuanjiang Basin is crucial for understanding the development direction of soil erosion in the Longchuanjiang Basin.Taking the Longchuanjiang Basin as the research background,the paper selected the purple soil covered by the eucalyptus forest in Mouding County of Chuxiong Prefecture as the research object,and carried out the following experiments:(1)Collecting sample soil according to different soil types and vegetation types in the basin.Measured humus and its components,soil physical and chemical properties,and analyzed the correlation between humus acid and soil physical and chemical properties,soil nutrients,sampling points.(2)selected soil pH and soil Eh as impact factors,and used sulfuric acid,quicklime,L-ascorbic acid and ferric chloride to adjust soil pH to5.03,6.24,7.57(CK),8.54,9.15,and Eh values to 109 mV,141mV,173mV(CK),218 mV,240mV.Used soil columns leaching experiments to explore its effects on theloss of HA and FA in soil.(3)Studied the effects of soil erosion factor-slope on soil humus acid loss,and adjusted the slope to 10°,15°,20°,25°,30°.Determined the amount and rate of HA and FA dissolved in the filtrate.The research results are as follows:1.The distribution of humus carbon and humin carbon in this area is similar.Yellow brown soil eucalyptus sampling point 1> purple soil eucalyptus forest > purple soil evergreen broad-leaved forest > red soil dry land.The humus and humin carbon content of yellow brown soil eucalyptus forest sampling point 2 and sampling point 3is relatively low.The humic acid carbon content distribution: purple soil eucalyptus forest > purple soil evergreen broad-leaved forest > red soil dry land > yellow brown soil eucalyptus forest sampling point 1;fulvic acid carbon amounts were different,yellow brown soil eucalyptus forest sampling point 1> purple soil saplings bush sampling point 1> purple soil eucalyptus forest> red soil dry land.In this area.The content of humin was more than 50% of humus,and the content of humic acid was less than that of fulvic acid.The ratio of humic acid and fulvic acid showed that the degree of humification in the area was lower.There was a significant positive correlation among the soil humus component.Soil nutrient,organic matter,humus and its components were significantly positively correlated with elevation.Organic matter,humus and its components were significantly positively correlated with total phosphorus,total potassium and available potassium.Humus and humin were significantly negatively correlated with pH.Humin and humic acid were significantly positively correlated with soil Eh.Soil pH was significantly negatively correlated with soil Eh.2.The pH value affected the dissolution and dissolution rates of HA and FA.They increased with the increase of pH in the range of 5.03 to 9.15.At the pH=9.15,the dissolution and dissolution rates of HA and FA were much greater than the dissolution and dissolution rates of HA and FA at pH=5.03.HA and FA changed with time.HA dissolution increased firstly and then decreased,and FA dissolution gradually decreased with time.This is related to the adsorption of HA with soil particles in the initial stage of leaching.The dissolution concentration of FA in the eluate was greater than the dissolution concentration of HA.It is related to the hydrophilicity of FA.3.Soil Eh had an effect on the dissolution concentration and dissolution rate ofHA and FA.In soils with Eh ranging from 109 mV to 141 mV,the dissolution of HA and FA was larger,and FA>HA.And Eh of HA and FA in 218 mV to 240 mV soil was less and there was no obvious change trend.4.Slope affected the rate and the volume of soil humic acid dissolution.The initial runoff time was significantly negatively correlated with the slope.The soil HA showed irregular changes with time,and the soil FA showed a trend of rising first and then decreasing.The average dissolution rate of humic acid was the largest at 20°,the smallest at 10°,and the other three were not different.FA dissolution and dissolution rates showed: 15°>20°>25°>10°>30°.Critical slopes might occur between 15° and 20°.The slope mainly affected the ability of hydraulic erosion,which affected the loss of humus acid components.The change of HA in the soil after leaching was irregular under the influence of slope,but FA could migrate in leaching area with the slope.FA was more likely to migrate in the soil,which is related to the hydrophilicity of FA.The loss of humic acid in the Longchuanjiang Basin is related to soil pH,Eh and slope.Chemical factors such as soil pH and Eh are more significant to soil humus acid loss.The slope mainly affects the loss of soil humic acid in the horizontal direction.Understanding the factors affecting the loss of soil humic acid is essential to maintaining soil nutrients,meantime it lays a theoretical foundation for studying soil erosion in this area. |
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