Analysis On The Source Of Mild Pollution Soil And The Availability Of Heavy Metals In The Typical Farmland In Chang-Zhu-Tan Area

With the rapid development of urbanization in China,industrial residential and agricultural mixed belts have been formed in the periphery of mega-city and metropolitan area.Heavy metal pollution caused by human activities such as urban traffic,industrial and agricultural production has been brought into the farmland ecosystem through atmospheric subsidence,chemical fertilizer which makes the farmland soil suffer heavy metal pollution and the problem can't be neglected.This study in the typical mild pollution of farmland in Chang-Zhu-Tan Area:Tianhua village in Qingshan Country of Changsha County(QSP),Feilong village in Meiling Bridge Country of Xiangtan County(FLC),Qingguang village in Meiling Bridge Country of Xiangtan County(QGC),for the atmospheric heavy metal wet and dry settlement monitoring(18 consecutive months),Field micro-area test,greenhouse pot experiment.On the basis of preliminary investigation of heavy metal content in soil,the characteristics of heavy metal content in field main pollution sources and the effects of different pollution sources on Cr,As,Cd,Hg,Pb total and available content in farmland soil were studied.The main findings are as follows:(1)Atmospheric wet and dry deposition test:QSP,FLC,QGC atmospheric heavy metal wet and dry deposition concentrations in different seasons have significant differences,the lowest in summer,the highest in winter,and the trend of settlement concentration is inconsistent,the settlement flux of heavy metal elements in the spring,the largest occurrence of the lowest in autumn.Due to the effect of heavy metal wet and dry deposition in the atmosphere,QSP,FLC farmland soil pH reduced 0.07,0.08 units,the organic matter content increased 0.20,0.30 units,the soil Cr,As,Cd,Hg,Pb total content have a small increase,and Pb increase more obvious,QSP,FLC increased by 30%,25.6%,the As,Cd and Pb available content increased,and Cd available content increased by 5.01%and 8.82%in QSP and FLC soil.Through correlation analysis,the annual precipitation fluxes of heavy metals in the atmosphere were significantly positive correlation with the content of heavy metal in soil,which indicated that the change of the available content of heavy metals in soil was related to the atmospheric wet and dry deposition.Through the effectiveness analysis,the efficiency coefficients of As,Cd and Pb in QSP and FLC farmland soil increased obviously,and the Cd increase was most obvious,two test sites increased by 25.2%and 7.2%.(2)Pot experiment in greenhouse:the effects of different fertilizers on soil pH,organic matter content,total and available heavy metal content were significant difference.Fertilizer treatment can significantly increase soil pH by 58.4%.Pig manure,chicken manure,commercial organic fertilizer,milk vetch treatment can significantly improve the content of soil organic matter,in which the content of organic matter in milk vetch increased by 43.5%.The application of different fertilizers can significantly increase the Zn total content in the soil,and the effect of compound fertilizer treatment is more obvious,the Zn total content in the reddish clay soil and alluvial sandy soil is increased by 27.8 and 27.7%.The pig manure treatment in the reddish clay soil can decrease the Cu available content by 24.3%;Applying different fertilizers has increased the Zn total content in soil,and the treatment of commercial organic manure can increase the Pb total content effectively by 7.26%.The Cd available content was significantly reduced by the treatment of milk vetch,and the effect of pig manure was reduced by 30.2%.The effect of different fertilizer treatments on Cu available content was not significant in the farmland soil,and the Zn,Pb and Cd available content was increased.The Cd available content was increased by using commodity organic fertilizer,compound fertilizer,milk vetch,and the compound fertilizer treatment was increased by 30.6%.(3)Field micro-region test:sewage irrigation,straw return field,lime regulation treatment on farmland soil pH,organic matter content were significant difference.Sewage irrigation treatment reduced soil pH value of 0.12 units,straw returned to the field,lime regulation treatment to increase soil pH value of 0.14,0.19 units;sewage irrigation,straw return to field treatment increased soil organic matter content 0.10,0.14 units,lime regulation treatment to soil organic matter content is not obvious.Sewage irrigation,straw returned to the field,the lime regulation treatment both increased the heavy metal total content in the soil,the Cd total content in the soil of sewage irrigation treatment increased by 9.76%;the effect of sewage irrigation,straw returning field and lime regulating treatment to the heavy metal total content in soil was significant,while sewage irrigation and straw returning to field increased the available content,the Cd available content increased by 5.88%,5.56%.The lime regulation treatment reduced the heavy metal available content in the soil,the Cd available content decrease most obviously by 30.6%,through the validity coefficient analysis,the lime regulation treatment Cd validity coefficient reduces by 32.3%.