| In order to reveal changes in characteristics of heavy metal elements arsenic (As), cadmium (Cd),chromium (Cr), copper (Cu), mercury (Hg), nickel (Ni), lead (Pb), and zinc (Zn) in the oasis drip irrigationcotton soil. Cotton field cropping of8a,14a,20a,25in Shihezi for the research object, selected referencestandard with Xinjiang gray desert soil elements background, evaluation of the enrichment of heavy metalsand ecological hazards. By correlation analysis, factor analysis and cluster analysis to analysis of possiblesources of heavy metals in cotton fields.The main conclusions are as follows:(1) By difference analysis about heavy metals content in the different continuous cropping cottonfield, F value of differences significant elements expressed as Zn> Pb> Cd> Cr> Cu> Hg> As> Ni, showedthat the change of Zn full amount change by cotton fields even the greatest impact for the impact of years,while the total amount of Ni relatively minimal changes.(2) Comparison of average content of heavy metals in soil and the background values of Xinjiangelements in cotton gray desert soil, Cr, Pb, Zn, Cd strongest element enrichment, the mean value of Nielements in the background almost the same. Heavy metals exceeded by the four plots frequency statisticsshows:the excessive frequency of Cr, Zn element are highest in each cotton field, the highest degree ofaccumulation, and the frequency of Cd, Cu, followed by the elements, Ni element content than theminimum background values.Compared with "Soil Environmental Quality Standards"â…¡(GBl5618-1995),the excessive situation of Cd is most serious.(3) Geological accumulation index for each Cropping Cotton Soil heavy metal accumulationcondition evaluation shows: Cr, Hg, Pb geological accumulation index showed a gradually decline incropping8a,14a,20a,25a of the cotton fields, the contamination level of moderate pollution level todecrease slightly-moderate pollution level. Zn, As accumulation index element in the cropping8a,14a,20a,25a cotton fields showed a gradual increasing trend of pollution by the no pollution levels rise to mild-moderate pollution levels, the cumulative index of Cd, Cu elements in the cropping8a,14a,20a in thecotton fields showed a gradual increasing trend, while in the cropping25a cotton fields has declined. Cdpollution in the cropping20a cotton fields showed the highest level, the pollution level to moderate-strongpollution levels, but pollution levels are moderate in the other three years of the cotton fields. Cu elementoverall showed a mild-moderate pollution levels.Ni element in the overall level of no pollution.(4) Accumulation assessment for classification about heavy metal in each cropping cotton soil whichby the Potential Ecological Risk Index showed: As, Cr, Cu, Ni, Pb, Zn elements potential ecological risksharm degree were mild; while the potential ecological risk harmful levels of Cd in the cropping8a,14a and25a cotton fields have reached a strong potential, and ecological risk also arrived strong degree in thecropping20a cotton field; Hg in the cropping8a cotton field up to a strong level of risk, also have reachedmoderate level of risk in the cropping14a,20a and25a cotton fields. Comprehensive potential ecologicalrisk index RI of the eight heavy metals in cropping20a cotton field at the highest to and arrived a strong degree.(5) Based on correlation analysis of the content of heavy metals with the physical and chemicalproperties in soil, combine with the result of factor analysis showed that: the main source of heavy metalsin the cotton soil are "fertilization factor","traffic factor","natural source factor". combined with resultof the cluster analysis shows that in the cotton soil, As,Cd mainly come from fertilizer;Cu and Hg aremixed source elements; Ni and Cr strongly influenced by soil parent material; Pb strongest affected bytransportation, while the cumulative degree of Zn affected by fertilizer application and traffic factor in thesoil. |
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