| With the rapid development of economy,the situation of heavy metal pollution in agricultural land in China continues to deteriorate.Heavy metal elements can not be degraded in the soil.Its migration and accumulation will not only affect the regional ecological security,but also bring potential harm to people’s health.Therefore,it is very meaningful to pay attention to and study the pollution status and migration law of heavy metals in soil.This paper first analyzes the contamination of Cd,Ni,As,Zn and Cu in the soil in the study area.Then the migration and accumulation of heavy metals in 0-40 cm and 40-80 cm soil under flooded irrigation were studied.On this basis,the migration of heavy metals in 0-80 cm soil under deionized water flooding,alternate wetting and drying with deionized water and flooding with p H = 5.3 were studied,and the dynamic model of leaching and release process was established to analyze the environmental geochemical behavior of heavy metals in soil.(1)In the evaluation of soil heavy metal pollution in the study area,the average pollution degree of heavy metal elements in each sampling point evaluated by Geo-accumulation index method was Cd > Ni > Cu > Zn > As.Cd is in moderate pollution,Ni is in non-moderate pollution,and Cu,Zn and As are in non pollution state.The evaluation result of Geo-accumulation index based on triangular fuzzy number is that Ni is moderately polluted and Cu is non-moderate polluted.(2)In order to study the effect of deionized water flooding irrigation on heavy metal content in soil column composed of 0-40 cm and 40-80 cm depth soil,it was found that the heavy metal content continuously migrated to the deep soil column during the irrigation process,but its impact on different heavy metals was different.The changes of four heavy metals in soil column leaching can be divided into two stages: the first stage changes sharply and the later stage is relatively stable,In general,the contents of Cd and Ni in the leaching of 0-40 cm soil column were higher than that of 40-80 cm soil column,while the content of Cu in the leaching was opposite,and the content of Zn changed greatly in the leaching.(3)In this paper,the migration and change process of heavy metals in eachlayer of soil column under deionized water flooding irrigation,drying-wetting cycle with deionized water and flooding with p H = 5.3 were studied.With the growth of irrigation time,heavy metals in the surface layer continuously migrated to the lower layer.Different irrigation methods and different irrigation time had different effects on the distribution of different heavy metals.The migration rate of Cd and Cu to deep layer under the condition of p H = 5.3 was higher than that of deionized water flooding and deionized water drying-wetting cycle.The results showed that the migration rate of Ni content in the later stage was p H = 5.3 higher than that of deionized water flooding irrigation,and the dry wet alternation of deionized water.Under the condition of p H = 5.3,the leaching accumulation was slow in the early stage and enhanced in the later stage.(4)Under the three irrigation modes of deionized water flooding,drying-wetting cycle with deionized water,and flooding with p H=5.3,the concentration and cumulative release of Cd,Cu,Ni and Zn in leaching can be divided into two stages,rapid change in the early stage and slow change in the later stage.The dynamic equation was used to simulate and fit the leaching process of the cumulative release of Cu,Ni and Zn with time.It was concluded that the first-order reaction kinetic model was not very suitable for each heavy metal,while the double constant rate equation and parabolic diffusion equation had a higher fitting degree for each heavy metal. |
PDF Full Text Request