| In recent years, with the rapid development of industry and agriculture, the soil heavy metal pollution aggravate gradually, it has brought a serious threat to the ecolodical security and the survival of human health. The northern tableland area of Xianyang belongs to the part of Weibei dry highland, and this region is an important base for coal, apple and grain. Because of the coal mining enterpr ises discharge "Three wastes", and a large number of people use pesticide and fertilizer in cultivating, which has brought in more severe soil heavy metal pollut ion, therefore, the study of soil heavy metal pollution has an important significan ce for the coordinating development of the local social, economic and ecological environment in this region. In this paper, we use index evaluation method, risk a ssessment method, and use GIS and geo-statistical method to make a comprehens ive evaluation of soil heavy metal pollution in this study area, and use the buffe r analysis and overlay analysis to quantitative analysis of the influence factors of soil heavy metal pollution such as coal mine, towns, roads, rivers, and use the s oil heavy metal accumulation prediction model to predict the space-time change t endency of soil heavy metal in the future, its main contents are as follows:(1) The content of As, Cr, Ni respectively increases with the increase of soi 1 depth, the three kinds of heavy metal concentrate in the depth of soil layer, th e content of Cu, Pb, Zn respectively reduces with the increase of soil depth, the y mainly concentrate in the soil surface, namely, the surface enrichment effects. As and Cr, Cu, Ni, Pb, Zn, Cr and Cu, Ni, Zn, Cu and Ni, Zn, Ni and Zn hav e significant positive correlation, so their pollution source is likely same, Pb and Cr, Cu, Ni, Zn have no significant correlation, they may be have different pollut ion sources. In principal component analysis, the first principal component is As, Cr, Ni, which illustrate that the pollution degree of the three kinds of heavy met al is higher proablely, the second principal component is Cu, pollution load time s, the third principal component is Pb, the fourth principal component is Zn, Zn is non-pollution. Organic matter and Cr, Cu, Ni, Pb, Zn present positive correlati on significantly, and As present positive correlation significantly. PH and Cr, Cu, Ni present positive correlation significantly, PH and As, Pb show negative correl ation significantly. Clay, fine silt, medium silt, coarse silt and most of the heavy metals present positive correlation, fine sand, medium sand and most of the heav y metals present negative correlation, coarse sand and Cr, Cu show positive corr elation, and As, Ni, Pb, Zn show the trend of positive correlation.(2) As, Cu, Ni, Pb and Zn are in line with the exponential model, Cr is in line with spherical model. As, Cr, Ni have a moderate spatial correlation, Cu, P b, Zn have a strong spatial correlation. From the point of range, the current sam pling interval is reasonable for the As, Cu, Pb. The range of Cr, Ni, Zn is bigg er than sampling interval, so they can undertake large scale sampling appropriate to expanded scale in order to save manpower and material resources, but the n ugget value of Cr is bigger, small scale sampling is still reasonable. The high c ontent of As, Cr, Cu, Ni, Zn are mainly distributed in the southeast of Changwu county, the southwest and the east of Bin county, the west of Yongshou, the no rtheast of Xunyi, the east of Chunhua, the high content of Pb is mainly distribut ed in the noutheast of Changwu county, the noutheast of Yongshou, the southeas t of Bin county, the southwest of Xunyi, the most area of Chunhua. The high c ontent of As, Cr, Cu, Ni, Pb, Zn are mainly distributed in the relatively high alt itude and high slope. The high content of As is mainly distributed in shady slop e, and the high content of Cr, Cu, Ni, Pb, Zn are mainly distributed in sunny si ope. The high content of Cr is mainly distributed in Yellow food soil, and the high content of As, Cu, Ni, Pb, Zn are mainly distributed in Dark loessial soil. The high content of Pb is mainly distributed in farmland, and the high content o f As, Cr, Cu, Ni, Zn are mainly distributed in orchard.(3) Using the Nemerow index evaluation, As, Cr, Ni are in a state of light pollution, Cu, Pb, Zn are in a state of non-pollution, and the overall is in a stat e of light pollution. Using the Geoaccumulation index evaluation, As, Cr, Ni are in a state of non-secondary pollution, Cu, Pb, Zn are in a state of non-pollutio n. Using the Pollution load index evaluation, the overall is in a state of seconda ry pollution. Using the Potential ecological risk index evaluation, As belongs to medium hazard degree, Ni, Cu, Pb, Cr, Zn respectively belongs to minor damage, and the comprehensive potential ecological harm belongs to minor damage. The coal mine has the biggest influence on As, Cr, Cu, Ni, the town times, and the road has the biggest influence on Pb, the coal mine times. In terms of single fa ctor pollution evaluation, the Nemerow index method and Geoaccumulation index method are suitable for evaluation of As, Cr, the Geoaccumulation index method is more suitable for evaluation of Cu, Ni, Pb. In terms of comprehensive pollut ion evaluation, the Pollution load index evaluation is more suitable for comprehe nsive evaluation of heavy metal pollution in this region.(4) Compared with the soil heavy metal pollution evaluation in 2014, in the optimistic scenario, the soil heavy metal pollution degree is significantly lower in 2030, in the no mutation scenario and pessimistic scenario, the soil heavy metal pollution degree are increased in 2030, and the pollution degree of pessimistic sc enario increase a lot than the pollution degree of no mutation scenario. Through the survey on the field and review of the outline of the Shaanxi province gover nment, we can preliminary judgment that the soil heavy metal pollution situation is most likely between optimistic scenario and no mutation scenario in 2030. |
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