| Ningxia Plain is alluvial formed by the Yellow River,and it is an important commodity grain base in China.At the same time,Ningxia Plain is also the main part of Yanhuang economic zone.The economic development of this area is not only related to the economic development of the western region of the country,but also crucial to the industrial layout and international cooperation of our country.However,in recent years,the problem of heavy metal pollution caused by the rapid development of agriculture and industry in Ningxia Plain has become increasingly prominent.In this study,the farmland(A and B areas)and Shizuishan industrial park(area C)of the Yellow River irrigation area in Ningxia Plain were taken as the main research areas,the water samples,topsoil samples,rhizosphere soil samples of different plants and crop corn samples were collected,respectively,and the content level and pollution characteristics of 11 kinds of heavy metals(As,Cd,Co,Cr,Cu,Mn,Ni,Pb,Sn,V,Zn)in the above environmental samples were analyzed.The interaction of heavy metals in water-rhizosphere soil-corn(root,stem and leaf)was studied by linear regression method,and the pollution sources and migration regularity of heavy metals in farmland planting system were investigated.Meanwhile,absolute principal component analysis multiple linear regression(PCA-MLR)and positive matrix factorization(PMF)models were used for source apportionment of heavy metals in the soils of two land use types(the farmland irrigated by the Yellow River and industrial park).This study compared the advantages and shortcomings of PCA-MLR and PMF models,and based on the results of source analysis,put forward the corresponding control suggestions for heavy metal pollution in the farmland irrigated by Yellow River and industrial park.The results showed that:All the water samples in the Yellow River diversion irrigation area are in the safe level,and there was no significant difference in the heavy metal contents in the water samples of the main,branch and drainage channels of the Yellow River in this area.However,due to the influence of agricultural and industrial pollution in the upper reaches,the heavy metal contents in the water sample from the lower reaches of Ningxia section of the Yellow River was the highest.The contents of Cd,As,Zn,Pb,Ni,Cr,Mn,Sn and Cu in rhizosphere soil of different plants were all higher than the background values of Ningxia soil environment,and Cd and As had reached the serious ecological hazard(160<Eri<320)and severe ecological hazard(Eri>320),respectively.Moreover,the content of As,Cd,Cr and Pb in corn exceeded the standard limit of national food safety standard limit of pollutants in food(GB 2762-2012).In the system of water-rhizosphere soil-maize(root,stem and leaf),water and rhizosphere soil are the direct sources of heavy metals in maize.We find that heavy metals in water and rhizosphere soil can promote the absorption of heavy metals in roots,stems and leaves of maize.At the same time,stems and leaves of maize showed that the accumulation and transportation ability of the same heavy metal in different parts of maize were different,and the accumulation abilities of different heavy metals in the same part of maize were also different.In addition,we also found that the synergistic effects of different heavy metals in different parts of maize were different,even if the heavy metals in water or soil do not exceed the relevant national standards,they will also have a certain toxic effect on plant.And the interaction between the same heavy metal and other heavy metals in the roots,stems and leaves of maize was also different.By comparing the statistical parameters of PCA-MLR and PMF and the results of soil source apportionment,we found that the statistical parameters of PMF were better than those of PCA-MLR in the process of source apportionment of soil heavy metals of two different land use types,and the PMF had more advantages in distinguishing and identifying complex covariant sources.According to the results of source apportionment,we also found that the analysis results of the two models have certain guiding significance for the farmland with light pollution and simple pollution source in the Yellow River diversion irrigation area.However,for industrial parks with heavy pollution and complex pollution sources,PMF model had more advantages.The heavy metal pollution of farmland soil in the Yellow River irrigation area mainly came from agricultural pollution(contribution rate of 57%=pesticide 17%+chemical fertilizer 14%)and the Yellow River irrigation(contribution rate of 26%),respectively.The overuse caused by the low utilization rate of pesticide and chemical fertilizer was the main reason for the contents of As,Cd,Cu and Pb in the farmland soil of the study area to exceed the standard seriously.Therefore,it was essential to scientifically calculate the application plan and promote formula fertilization by soil testing according to different farmland types.In addition,the sediment brought by irrigation from the Yellow River had increased the background value of heavy metals in the soil of Ningxia plain.Therefore,it was necessary to adopt "limit emission" instead of "limit emission standard" to control the heavy metals pollution in the sediment of the Yellow River,and strengthen the strict control and supervision of the pollution emission of enterprises along the Yellow River.Heavy metal pollution in Shizuishan industrial park mainly came from various local industrial production(contribution rate of 59%)and air pollution(contribution rate of 31%).Among them,the steel manufacturing industry had the greatest impact on heavy metal pollution in study area.The local government should specifically control the soil heavy metal pollution in each process of factory production to ensure the clean production of the whole process.In addition,the air pollution in this area mainly came from the busy industrial transportation in the park.Therefore,the standardization of transportation vehicles and materials and road greening should be given more attention. |
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