Characteristics And Influencing Factors Of Soil Cadmium Content In The Core Area Of Chengdu Plain

With the rapid development of industry,agriculture and urbanization,the problem of soil heavy metal pollution has become the focus of global attention.Accurately grasping the characteristics and spatial variation of soil heavy metal content in the region is the key and prerequisite for the prevention and control of heavy metal pollution in soil.However,there are relatively few studies on the factors affecting soil cadmium（Cd）content in the core area of Chengdu plain,and the analysis is not thorough enough.Based on this,in this study,the Cd content in the core area of Chengdu plain was taken as the research object,and the human factors（land use patterns,traffic roads,etc.）and natural factors（grown soil parent material,soil types,water systems,etc.）were deeply analyzed for the cadmium content of the soil in the study area.To provide a theoretical basis for the rational use of land in the study area and effective control of soil Cd pollution.The main conclusions are as follows:（1）The Cd content in 0～100 cm soil in the study area is between 0.20～0.37 mg·kg^-1,which is between the level I and II pollution level of the national soil environmental quality standard,and the trend of decreasing gradually from the surface to the surface in the vertical section.The coefficient of spatial variation of Cd content in soil layer of 0～60cm soil is between 34.69%～63.79%,mainly influenced by structural factors and random factors.The Cd content of 60～100 cm soil is less than 25%,which is a strong spatial autocorrelation,mainly influenced by structural factors.The spatial distribution of soil Cd content generally shows a trend of decreasing from south to north.0～20 cm soil Cd pollution is in the light to moderate pollution,20～100 cm soil Cd pollution degree is low,basically in no pollution,the cancer risk is within acceptable range.（2）The effect of soil parent material on the content of Cd in 0～60 cm soil layer was not significant,and the Cd content in the soil layer of 60～100 cm soil was significantly affected,and the content of Cd in the soil developed by the purple alluvium was significantly higher than that of the upper Pleistocene yellow clay.Soil sub-groups had significant influence on the Cd content in 0～40 cm soil layer,which showed that the content of Cd in the new soil was significantly higher than that of percogenic paddy soil,take off the gley paddy soil and Waterlogged paddy soil.Soil genus has a significant effect on Cd content in 0～40 cm soil layers.The Cd content in 0～20 cm sand soil was significantly higher than that in infiltration yellow mud field,infiltration grey tide field,infiltration gray brown tide field,infiltration purple tide field,off-land subduction tide field,and eel-fed gray tide field.The Cd content of 20～40 cm soils in new accumulating lime sand is significantly higher than that in infiltration yellow mud fields and wolfberry-cultivated grey tidal fields.Soil sub-groups and soil genus had no significant effect on Cd content in 40-60 cm and 60-100 cm soils.（3）Different land use patterns in the study area have a significant effect on the Cd content in 0～20 cm soil,which shows that the Cd content in agricultural and forestry land is significantly higher than that in rice-vegetable,rice-rape and garden land.The effect of land use on soil Cd content in 20～40 cm,40～60 cm,and 60～100 cm soils was small,and they did not reach significant differences.（4）The influence of water system on soil Cd content in 0～20 cm soil layer is mainly within the range of 12 km,the change range of soil Cd content in 20～40 cm and 40～60 cm soils is mainly within 10 km,the effect of water system on Cd content in 60～100 cm soil was not significant.（5）The traffic road in the study area has a significant effect on the soil Cd content in the soil layer of 0～20 cm.The content of Cd content in soil is gradually decreasing with the increase of road distance within 2 km distance from the distance road,and the decrease is more obvious in 0.5 km,but there is no significant effect on the Cd content change of20～100 cm soil.In summary,the Cd content in the surface soil of the study area is higher than the national soil environmental quality grade II standard,which is in light to moderate pollution,and the Cd content in the soil from the surface layer is gradually reduced.The Cd content in surface soil was affected by land use,traffic roads,water system and soil type,and the impact of Cd content on soil surface was gradually weakened from the surface layer.The Cd content in the 60～100 cm soil was mainly affected by the parent material.