| In order to ensure the quality and safety of soil and agricultural products,the identification of soil pollution sources,the analysis of pollution migration paths,the transport of cadmium in the soil-rice system,and the priority screening of cadmium inhibition and control are particularly worthy of attention.The systematic integration of soil pollution sources and migration paths and cadmium transport,it will provide a scientific basis for designing suitable pollution source mitigation strategies,agricultural products and human quality and safety.Current research tends to combine multiple methods for source identification,and only analyzes soil indicators,and there are limitations in the scope of application and application promotion.Therefore,based on the analysis of pollution sources,this paper will study the migration path of soil pollution and the transport and inhibition of cadmium in the soil-rice system.Mainly from the following five aspects:identification of heavy metal pollution sources and calculation of contribution rate,calculation of similarity of heavy metal pollution sources in regional plots,machine learning to fit pollution migration paths,transport of cadmium in soil-rice system,and priority of cadmium inhibition and control level filtering.The main results of this paper are as follows:(1)Taking Xiangtan County as the research object,the correlation analysis and principal component analysis were carried out on the soil index data,and finally:there are five main pollution sources in the study area,which are mixed sources(mining sources+natural sources)with Fe,Se,Ca,Mn,As,Cd,and Zn as the main loads.With Mg and Fe as the natural source of the main load elements,industrial sources dominated by Cr and Ni,the transportation source is mainly composed of Hg,Pb and other elements,and the agricultural source is mainly loaded with Cu and Zn.(2)The contribution rate of each pollution source to soil Cd,As,Pb,and Hg was calculated by multiple linear regression.Based on the contribution rate,the cosine similarity was used to calculate the similarity degree of each heavy metal pollution in the regional plot.Finally,the mixed source(mining source+natural source)contributed the most to soil Cd and As,accounting for 40.88%and 57.86%,respectively.The contribution of traffic source to soil Pb and Hg was larger,accounting for 45.97%and49.36%,respectively.The similarity results show that the proportions of high-value areas of Cd,Hg,As,and Pb in the soils of each plot are 92.67%,95.02%,75.64%,and 95.23%,respectively,and the distribution of heavy metals Cd,Hg,As,and Pb in the regional plots is similar.generally higher.The similarity of As in soil is lower than that of other heavy metals,and the low similarity is mainly reflected in the low concentration areas mainly in the Middle East-Central South.(3)Based on the similarity calculation result data,the random walk algorithm is used to fit the pollution migration path,and finally:As pollution migration was mainly related to aquaculture and nano-zinc oxide factories,and mainly migrated through the Juanshui River,Xiangjiang River tributaries,Qingshan River and other rivers.The migration of Cd pollution is mainly related to coal mines,zinc factories,and transportation.The migration of Hg pollution is mainly related to the construction material factory and the nano-zinc oxide factory,and it mainly migrates through the southeast wind direction and the tributaries of the Xiangjiang River.The migration of Pb pollution is mainly related to building material factories,coal mines,and nano-zinc oxide factories,and mainly migrates through the tributaries of the Juanshui River,the Lianshui River and the Xiangjiang River.(4)Based on PCA factor loading data,the contribution rates of different sources to soil cadmium(Cd_s),activated cadmium(Cd_a)and rice cadmium(Cd_r)were calculated,and based on six townships,the contribution rates of cadmium from different sources were compared.Spatial distribution characteristics,and finally obtained:There is an imbalance in soil cadmium activation and accumulation capacity from different sources.Among them,mineral sources are the main contributors among the five sources,accounting for 50.3±11.1%.The contribution rates of mineral sources to Cd_r,Cd_aand Cd_sare 50.57%,61.25%and 39.11%respectively,the contribution rates of traffic sources to Cd_r,Cd_aand Cd_sare 40.08%,26.82%and 30.12%respectively,and the contribution rates of animal husbandry sources to Cd_r,Cd_aThe contribution rate ratios of 21.90%,1.74%and 8.76%of 21.90%,1.74%and 8.76%.These three sources of rice have strong cadmium accumulation capacity,and necessary prevention and control measures should be taken.The results of spatial distribution showed that cadmium pollution showed significant spatial heterogeneity at the regional scale,and the transport performance of cadmium in different sources was different.(5)Based on the data of the contribution rates of different sources to Cd_r,Cd_a,and Cd_s,the values of Cd_r/Cd_sand Cd_a/Cd_sof each pollution source were calculated,and the final result was:Mineral sources and traffic sources were the main contributions,and Cd was easily enriched by rice,which should be prioritized.Agricultural and natural sources are also important sources of soil cadmium,but the accumulation of cadmium in rice is limited.There are eight combinations of Cd transmission laws,and eight control measures are proposed respectively,the main control measures are source resistance control,enhanced cadmium adsorption,and leaf surface resistance control. |
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