Temporal And Spatial Characteristics And Source Identification Of Heavy Metal Contamination In Typical Region Cropland

With development of the social and economic, people’s living standards has improved and the qualityand safety of agricultural products attracts people’s attention. Only safe agricultural environmentprovide safe agricultural products, so the analysis of agricultural environment variation and influencingfactors become popular. In this paper, Taihu is taken as a typical area and typical heavy metals such asCd, Pb, Hg, As are research materials. The background and present values of heavy metals in the soilare collected and the statistical analysis, geostatistical technology are combined. The time and spatialvariability of both overall area and local area have been studied with the reason of the variation. Theresults are as follows:1. The overall descriptive statistics of background data and present data were carried out. Except for Hg,the content of other three kinds of heavy metal (mean and median) were generally constant or trifleincreasing, indicating that there is accumulation of heavy metals in the certain research area. Aftercomparing the coefficient of variation, we found the variability of Cd and Pb enhanced, indicating thathuman disturbance affect strongly. The partition statistics showed that in Dongting Hilly present contentof Cd and Pb grew,and Cd were nearly two times of that of the background. The content of Hg declinedin multiple sub-districts, especially that in Yilichangxing Mountain. The content of As remained stablein the past20years.2. Applying many methods including spatial clustering, global trends, semivariogram modeling andspatial interpolation to analyzed spatial characteristics of heavy metals in soil during the backgroundand the current period, the results showed that in the respect of Cd, the background content in southernand eastern regions of Taihu Lake were lower, on the contrary, the current content are higher than otherarea. In the respect of Pb, the Pb content in Shataiyanjiang plain were high during both the backgroundand current period. In the respect of Hg, high value distributed scattered during the background period,and high-value area were found in southern and northern area during the current period. In the respect ofAs, the global trend is basically flat, As content in the western region during the two periods were higher.The nugget effect of four heavy metals were moderate spatial correlation during the two periods,indicating the heavy metal content in soil were affected by humans during the two periods.3. The variability of soil heavy metals during the two periods were analyzed, the results showed that inthe respect of Cd, hot spots (high-high clustering points) distributed more dispersed whichconcentrated in the southern and eastern region. In the respect of Pb, hot spots remained stable, and Pbcontent in southern region increased slower than that of northern region. In the respect of Hg, thedistribution of soil Hg during the two periods had small changes, and Hg content in the southern regiondeclined intensly. In the respect of As, the number of hot-spots area increased, and the Shataiyanjiangplain changed from low-value region to high-value region, indicating that the As content in this regionincreased faster.4. To analyze how the industry affected metals content in soil, the map of industry&mineral spots superimposed with spatial distribution were draught, the results showed industrial Minerals is one of theimportant factors of soil Cd, Pb, As content. Contrasting heavy metals in soil at different distances fromthe roads to research the transportation effect, the results showed transportation was the main factoraffecting Cd and Pb content in soil instead of Hg and As.