| Soil is a non renewable natural resource,is the material basis for human survival and development,and plays an irreplaceable role in ensuring China's food security.When heavy metals enter the soil,they are not easy to be degraded by microorganisms,which will cause serious damage to the soil and crops.In September 2019,general secretary Xi Jinping stressed the importance of paying attention to the development of the the Yellow River River Basin.At the same time,as an important reserve land resource reserve in Henan Province,soil quality is related to the grain production and safety.It is of great practical significance to study the soil quality of the cultivated land in the Low-lying land area of the Yellow River.In this study,the beihewa area of Kaifeng section of the lower Yellow River is taken as the research area to divide the grid,determine the number of soil samples,sample and experiment,determine the content of heavy metals in three different soil layers(0-20 cm,20-40 cm,40-60 cm)of eight heavy metals,and use SPSS 22.0,GS + win 9.0 and other software to process the data;use Arc GIS In 10.3,the methods of geostatistics and spatial interpolation are used to carry out spatial analysis(outlier and variogram)on 8kinds of soil heavy metals in the study area.The pollution situation of soil heavy metals is analyzed by many pollution evaluation methods such as Nemero index method.The pollution degree of heavy metals is evaluated and graded according to the potential ecological risk evaluation index model,and the main component analysis and enrichment factor are used Analysis method to determine the source of pollution.Combined with the vertical profile migration characteristics and leaching migration analysis of heavy metals in soil,the vertical profile analysis of heavy metals in soil with heavy pollution degree is carried out,including the content,spatial distribution trend,pollution evaluation and leaching rate of heavy metals in different soil layers,and the final conclusion is drawn.The conclusions of this study are as follows:(1)In the study area,Cd and Hg elements are more polluted,while other elements are less polluted.In the study of heavy metal content in surface soil,the variation coefficient of Hg is the largest,which is more than 1.The average content of 8 kinds of heavy metals in soil was compared with the background value of tidal soil in Henan Province.Except for Cd,the average content of 7 kinds of heavy metals did not exceed the standard.The content of Cd in the soil in the study area was seriously over the standard,and the pollution was relatively serious.The content of other heavy metals was within the background value of tidal soil,and the pollution was relatively light,and the overall soil quality in the study area was better.According to the Nemero index method,there are less clean areas in the study area,most of the soil is in a state of pollution,and the main pollution is light pollution,while the moderate and heavy pollution is less.According to the pollution load index method,the overall pollution level of the soil in the study area is relatively low,only a small part of the regional soil is polluted to a certain extent,resulting in pollution load.According to the method of cumulative pollution index,there is no accumulation of Cr,Cd and Hg in the soil of the study area.The accumulation of Cd and Hg is more serious,and the accumulation of other elements is less.The overall accumulation degree of the soil in the study area is less and the pollution degree is not high.(2)The overall trend of pollution in the study area is higher in the West than in the East.The eight heavy metals have a certain spatial distribution trend in space,and the pollution degree in the west is high.In general,the content of Cu in the East,West,South and north is higher than that in the middle;the content of Cr in the east-west direction shows a decreasing trend from east to west,with little change in the north-south direction;the content of Ni decreases from east to west and from north to south in space;the content of Zn and Ni has the same trend,with decreasing from east to west and from north to south in space;the content of Pb decreases from east to west and from north to south in space The content of Cd is thesame,and the peak value appears in the middle;the content of Cd changes little in the east-west direction,slightly less in the West than in the East,and higher in the South and north than in the middle;the content of as is generally higher in the East and West than in the middle,and decreases from north to south in the north-south direction;the content of Hg decreases spatially from east to west,and from north to south.(3)The heavy metal pollution in the surface soil was more serious than that in the inner soil,and the pollution decreased with the increase of depth.The pollution of Cd element is serious in the vertical section,and the pollution of Hg element is small in the whole.The average content of Cd element in the three layers of soil is higher than the background value of tidal soil in Henan Province,and Cd element is seriously over the standard.The maximum content of Hg element in three layers of soil is higher than the background value,and the average value is lower than the background value.The content of Hg element exceeds the standard,but the pollution is small.The content of Cd and Hg in the soil decreased with the increase of the depth of the profile,and the content of 0-20 cm in the surface soil was much higher than that in the other two layers.At 20-40 cm and 40-60 cm,the content of Cd elements in most areas is above 0.1 mg/kg.The pollution of Cd elements in the deep soil is still serious,which is also related to the heavy pollution of Cd in the surface soil.Cd element in 0-60 cm soil is in the overall pollution situation,and the pollution situation has a certain improvement with the increase of soil depth.In the 20-40 cm soil,the content of elements in the west is higher than the background value,showing the Hg pollution state.In the East,except for a small part of the southeast,it is lower than the background value as a whole.The total content of 40-60 cm elements is lower than 0.047 mg/kg,and no pollution has been formed.(4)The pollution source of vertical section in the study area is basically the same as that of surface layer.The leaching ratio of Cd and Hg is very low in the vertical section.The reason may be that there are less irrigation water sources in the study area,and the precipitation is less in the temperate continentalclimate zone,and the seasonal distribution is uneven.The heavy metals enriched in the soil surface have less opportunities to move down with the water resources,and the infiltration water flow is weak.Affected by the surface humus layer or other substances,a large number of heavy metals remain in the cultivation layer.The leaching rate of Cd element in plough bottom is higher than that in plough layer,which may be due to the fact that there is less farmland irrigation in the study area,but there is irrigation phenomenon.The Cd element in the soil surface infiltrates into plough bottom along with the flow of water,and the soil has poor water locking property due to the sandy soil in beihewa area,so the leaching rate of Cd element in plough bottom is higher than that in plough layer. |
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