| It is very important to study the spatial distribution characteristics and the risk assessment of soil heavy metals to ensure food safety and environmental safety.This study is divided into two layers to the collection of soil samples, surface sampling depth for 0 ~ 20 cm, sampling density for one point /4km2.A total of 499 points; deep sampling depth for 60 ~ 100 cm, sampling density for one point /16km2. A total of 128samples; center of each of the four surface is a deep layer samples.Using the principle of mathematical statistics and geostatistics, based on soil sampling analysis and GIS technology, take Qixia City in Shandong Yantai as an example, we study the semivariogram of total 8 kinds of heavy metals in surface soil of As, CD, Cr, Cu, Hg, Pb, Ni,Zn, construct the theoretical model, and make a systematic analysis of the spatial variation of8 kinds of heavy metal elements in soil.The correlation of terrain factor, land use type and heavy metal content of soil was discussed, and the characteristics of 8 kinds of heavy metal elements in soil were analyzed under different terrain conditions and different land use types.At the same time, the content of heavy metals in deep and shallow soil was compared and analyzed, and the source of heavy metal in soil and its influencing factors were discussed.Finally, the risk assessment of heavy metal pollution was made,in order to provide a reference for the management of the orchard in Qixia city.The main results are as follows:(1)Statistical result shows that the average of eight kinds of heavy metals in the topsoil are higher than the average content of background, but do not exceed the national secondary standard limits,and it compliance with appropriate safety standards of soil;(2)Comparative analysis of terrain factors showes that there are no significant correlation between the distribution of heavy metal elements and terrain factors.(3)The structural analysis shows that the spatial correlation of Cu、Cd and Zn are weak in the surface soil, it illustrate exogenous factors plays a larger influence for their distribution,and the rest of heavy metals are obvious spatial correlation in a certain range;(4)The comparison of different layers shows that there are different degrees of external sources soil of Qixia at the aggregate level, especially Cd、Cu、Hg、and Zn, the degrees are slightly heavier. The content of heavy metals in the topsoil of Qixia city is the result of parentmaterial and genous factors working together.(5)Comparative analysis of the type of land use showes that the content of Cr, Hg, Ni are little difference in the distribution of land-use types,As content is the highest in the land for construction,the content of Cd and Zn in unused land, grassland and woodland is above the garden, farmland and construction land,the garden is the largest content pf Cu,Pb highest content in arable land and construction land;(6)The results of soil heavy metal pollution risk assessment showed that the single factor pollution index Pi was Cu > Cd > Cr > Ni > Pb > Zn > Hg > As, Cu element was the highest contribution rate of soil pollution in Qixia city. Multi factor pollution assessment, from the whole point of view, the quality of heavy metals in Qixia City is in clean level, suitable for the cultivation of Yantai apple. |
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