| With the development of society and economy and the speeding up of urbanization course, the overspreading of cities and traffic constructing, industrial pollutant discharge and exudation, and irrationally apply of sludge and rubbish in cities, pesticide and fertilizer which contained heavy metal had made the pollution of environment more and more seriously. Therefore, heavy metal pollution aroused swinging attention at home and abroad. Accumulation of heavy metal in soil would lead to the potential pollution of urban ecology. Environment influence of urbanization course increased the loads of soil contaminated matter, and aggravated the accumulation of heavy metal in city-skirts and around traffic-line region, then affected the growth of propagation and endangers human safety.At present, there were rather more study on the spatial variability of soil physical and chemical properties at home and abroad. The study on soil physical properties were mostly concentrate on soil moisture, bulk density and mechanical composition; the study on soil chemical properties greatly involved organic matter, N, P, K, Ca, Mg, Zn, Mn and Fe. However, there was a little information on the spatial variability of soil heavy metal forms, and had no system study on the influence factors of soil heavy metal forms variance. The research on soil quality change emphasized particularly on nature courses, rarely took into account the influence of social and economic change on soil quality dynamic, or only had the simple logical concluding and general description on the influence of society and economy, did not introduce good mathematical method to demonstrating and analyzing. The evaluation of soil environment quality only depended on the change of total conent of metal, lacked the standard that evaluating soil environment quality referred to the content of soil heavy metal forms. Chengdu Plain locates in the west of Sichuan Basin which is famous for "the land of abundance". As a distinguished farming base in our country, the agriculture sustainable development and health of people were directly influenced by the quality status of soil. Chengdu Plain lies in the center of Sichuan Province and it's prosperous economy and human activities had affected the soil environment greatly. In recent years, the course of urbanization is speeding up, township enterprises developed quickly, living standard improved remarkably, devotion of the farming also increased. Industrial pollutant discharge randomly, irrationality apply pesticide, fertilizer and inconsequence farming measures, had aggravated the soil pollution, especially the pollution of soil heavy metal. Hereby, carrying through the study of soil heavy metal and the environment effect during the course of Chengdu Plain urbanization is so pressing.By taking alluvial paddy soil of Chengdu Plain for example, based on field investigation and lab analysis, this research charactered for the relation between urbanization and the status of society ecology status in the course of Chengdu Plain urbanization with soil heavy metal evolvement, also studied temporal and spatial variation of paddy soil heavy metal in "urban-suburb-rural section" in the core of Chengdu Plain and the affection caused by urbanization, the spatial variability and driving factors of heavy metal form, and the relation between different forms of soil heavy metal with quality of agriculture products. Suitable evaluating index and rationality assessment methods were selected, and then soil heavy metal threaten extent to the environment was educed. Meanwhile this research adopted grey correlated analysis method and BP Neural Network, and then opened out the relation between variety of soil heavy metal and driving factors, especially the society economic factor. Therefore, the influence of urbanization progress to soil heavy metal was forecasted more accurate. By using geostatistics to analyze the spatial variability characteristics of soil heavy metals and their form, furthermore, this study found the factors which attributed to the change of soil heavy metal and then tracked by Kringing interpolation analyses definitude the evolvement trend of soil heavy metal in the field. Though plant analysis then combined with the content of soil heavy metal, the relation between assimilate and cumulating of plant to the heavy metal with the content of various heavy metal forms in soil was discussed. Then the research brought forward estimating reference standard of the various forms of heavy metal to the environment effect of agiculture products. 1. Evaluation of soil heavy metal contamination in Chengdu PlainCd and Hg had the most points which exceeded standard in 197 points according to the second grade standard in GB5618-1995(Soi7 Environment Quality Standard). Cd had 17 points exceeded the standard, which occupied 8.63% of the total points and mostly distributed in Xindu, Shuangliu, Deyang and Dujiangyan; Hg had 12 points exceeded the standard, which occupied 6.09% of the total points and mostly distributed in Guanghan and Shuangliu. In addition, Cu had 7 points exceeded the standard, which greatly distributed in Pengzhou and Xindu; Cr had 2 points exceeded the standard in Shuangliu and Chongzhou; Pb only had 1 point exceeded the standard in Xindu; As had 1 point exceeded the standard in Guanghan; Zn had no point exceeded the standard. Because of lacking national evaluation the standard of F, this paper didn't evaluate the contamination actuality of soil F in Chengdu Plain.According to the first grade the standard in GB5618-1995 (Soil Environment Quality Standard), Cd, Pb, Hg and Zn had more than 40% of total points exceeded the standard, Cr had more than 25%of total points exceeded the standard, As had 15% of total points exceeded the standard. Simultaneously, the character of area in which soil heavy metal, F and As content exceeded the standard was different elements in the same area had great difference, the same element in different areas also was different.Contamination degree was evaluated by geology accumulation index method. The results indicated that, Pb, As and Cd in soil had about 50% of total points have been influenced by human activities in somehow degree, and Pb was the most obviously. The contamination grades of Pb had 1~4, but the major grades were the 1 and 2 grades. Simultaneously, the major grades had great distribution difference in the areas, which distributed in Xindu, Guanghan, Xinjin, Wenjiang, Pengzhou, Pixian, Deyang, Shuangliu and Chongzhou. As had three contamination grades 1-3, the major was the 1 grade, which distributed in Guanghan, some points in Qionglai, Pengzhou, Dujiangyan and Shuangliu had achieved the 2 grade of contamination grades. Cd had small contamination grades, only had two contamination grades 1~2, the major was the 1 grade, but its contamination areas were large, mostly distributed in Xindu, Deyang, Guanghan, Shuangliu, Xinjin and Pengzhou. Other elements such as Cu, Cr, Zn, Hg and F only had small scale were contaminated, the contamination grades was 1-2, and the major was the 1 grade. 2. The relation between content of soil heavy metal, F, As and time in Chengdu PlainBased on comparing between soil heavy metal, F, As content of soil points which were collected in 2002 and soil background content in 1982, this paper analyzed evolvement trend of soil heavy metal, F and As in the past 20 years in Chengdu Plain, and analyzed the elements which had obviously change and transfer in soil horizons in soil profiles. The results showed that, soil Cd, Pb, As and F content changed greatly as the influence of human activities in these 20 years. Except Wenjiang, Chongzhou and Dujiangyan, Cd content raised, it obviously indicated in Xindu and Jingyang. Pb content ascended most were in Xindu, Xinjin, Wenjiang and Guanghan, the next were Pixian, Jingyang, Qionglai, Dujiangyan and Shuangliu, and the other areas changed little. As content ascended obviously in Guanghan, Longquan, Shuangliu and Jingyang, it changed small in Dujiangyan, Xinjin and Wenjiang. F content dropped in whole area except Xindu, Shuangliu and Guanghan. The content of Cu, Cr, Zn and Hg changed slowly, but it had obvious difference in areas, such as Cu in soil content in Pengzhou, Cr in soil content in Shuangliu, Zn in soil content in Pixian and Guanghan, Hg in soil content in Guanghan all indicated distinctive ascend trend.Some elements had transferred distinctively in soil horizons according to analysis of soil heavy metal and F, As content in different soil horizons in 12 represent points. Soil Hg, Cd, Zn and Ascontent had obvious accumulation in 20-40cm soil horizon, which heightened 1.62, 1.33, 0.60 and 0.40 times respectively compared to soil background content and heightened 80%, 30%,40% and 25% compared to content in 0~20cm soil horizon. Pb, Cr and F assembled obviously in 0~20cm soil horizon, the average content of Pb and Cr in 0~20cm soil horizon was heightened 2.22 and 1.67 times than soil background content. The average content of soil F in 0~20cm and 20--40cm soil horizon was 628.3mg/kg and 567.3mg/kg, respectively. 3. Spatial variability and interpolation analysis of soil heavy metal and F, As contentThis paper analyzed the spatial variability of soil heavy metal and F, As content by the software ArcGIS9.0 such as semivariance and ordinary Kriging (OK). The results showed that, in isotropy semivariance model, the semivarigram values of Cd, Cu,Cr and Hg were expressed by Spherical model, Pb and Zn expressed by Index model, As and F expressed by Gaussian model. The ratio Nugget/Sill of the seven elements was 30%~40%, it indicated the ratio of random factor which control the content of the eight elements was high. But the ratio Nugget/Sill of Cr was 0.202, this indicated its spatial variability was controlled by structure factor. The content of soil heavy metal, F and As had influenced by human activities in Chengdu Plain because of the range of the eight elements was 20~60Km. So far, the influence extent was only indicated in big area and the influence intension was soft comparatively, but we should pay more attention to it.In anisotropy semivariance analysis, the semivarigram values of Cd, Cu and As were expressed by Spherical model, F was described by Gauss model. Cr accorded with Gauss model except for the direction of 0°, which was expressed by Spherical model. Pb accorded with Index model except for the direction of 90°, which was expressed by Spherical model. Zn accorded with Spherical model except for the direction of 45°, which was expressed by Index model. Hg accorded with Spherical model except for the direction of 0°, which was expressed by Gauss model. The variance extent of Cd was close in all direction, except in the direction of 45° for the sill of Cd was higher in the direction. The variance extent of Cu, Pb and As was the biggest in the direction of 135°, and distributed as zonal anisotropy. The variance extent of Cr and Hg was the highest in the direction of 0°, and accorded with zonal anisotropy characteristic. The variance extent of F was highest in the direction of and showed zonal anisotropy characteristic. Zn had close variance extent described by geometrical anisotropy in the four directions, but the variance range was difference, the biggest correlation range was 63.50km in the direction of 90°.Interpolation analysis of soil heavy metal and F, As content showed that the distribution trend of Cd, Cu, Pb, Zn, Hg, As and F content was obvious in study area. The content of Cd was increasedfrom southwest to northeast; the highest value (0.30mg/kg~0.65mg/kg) region was existed in the joint of Deyang, Guanghan, Pixian, Pengzhou and Xindu, and in the north of Pengzhou. The content of Cu was declined from northwest to southeast, the highest value (>36.0mg/kg) region existed in northeast, and in the joint of Chengdu, Xindu, Wenjiang and Shuangliu. The distribution of Pb appeared as strip, the highest value (>95.0mg/kg) region was existed in the line of Deyang-Guanghan-Xindu-Wenjiang-Xinjin, and in the north of Dujiangyan. The content of Zn was lower in around, higher in middle part, and the highest value (>120.0mg/kg) region only existed in Pixian and Wenjiang. The distribution characteristic of Hg content was higher in north part of study area, the highest value (>0.30mg/kg) mainly existed in some parts of Guanghan and Xindu. The content of As was increased from northwest to southeast, the highest value (>12.5mg/kg) region existed in some parts of Longquan, Deyang, Guanghan and Shuangliu. The distribution characteristic of F content was lower in northwest, southwest and the north of Deyang, was higher in southeast and middie part, the highest value (>750mg/kg) region existed in Shuangliu and Longquan, The highest value (130.0mg/kg~220.0mg/kg) region of Cr existed in small parts of north in study area, and in some parts of Shuangliu and Chongzhou. 4. Influences of the development of urbanization on heavy metals in soilApplying to data intensive technology of factor analysis, Index of socioeconomic factors which were constructed overall index, indirect index and direct index were classified and extracted. These index had effects on heavy metals, fluorine and arsenic. There were 10 in 1982 and 20 in 2002. Furthermore, in terms of scores of principal divisor 14 districts and counties in the centre of Chengdu plain were classified by taking advantage of clustering analysis. Through sequencing of grey degree of association between heavy metals in soil and factors (in 1982, in 2002), most highest and higher factors connected to degree of association with heavy metals were chosen in every region and computed major factors which can affect a variety of heavy metal content. The differences in different regions and overall influences of major factors on heavy metals, fluorine and arsenic were discussed.Factor analyses and region clustering analyses showed that, according to primary index after factor analyses, index which may affect heavy metal pollution were described as six major factors in 2002, including major socioeconomic production value, input of indirect pollution, and agricultural environment in soil, rural conditions, developmental rate and agricultural husbandry. Three major factors in 1982 about socioeconomic development, rural conditions and developmental rate were also obtained. Therefore, the ideal description of index obtained from major factors and analyticresults proved rationality of frame which consists of overall, indirect and direct drive index. Because of complicated conditions on economic development and ecological environment in study area, this study area (in 1982, 2002) were classified three through region clustering analyses. The first class contained Guanghan, Jingyang, Xindu, Shuangliu, Jingtang, The second class contained Longquanyi, Dujiangyan, Chongzhou, Pengzhou. The third class contained Wengjiang, Qionglai, Xinjing in 2002. The first class contained Shuangliu, Qionglai, Chongzhou, Xinjing, Pengzhou, Pujiang, Dujiangyan and Jinyang, The second class contained Longquanyi and Jingtang; the third class contained Xindu, Guanghan, Pixian and Wenjiang in 1982.Overall influences of major factors on heavy metals, F and As indicated that, the major influence factors of heavy metal content was single in 1982. However, the degree of impact of these factors in 2002 were socioeconomic level factors and development rate ones, which influenced content of As, Cr, Pb, Cu and so on. Meanwhile, the content of Hg, Cd and F was influenced by the factors of socioeconomic development, indirect pollution input and agricultural husbandry. The content of Cr, As Pb and Cu was influenced by the factors of indirect pollution input and soil agricultural environment fundamentally, the content of As, Pb and Cu had correlated to the factor of socioeconomic rate.Influence of different factors in different area (space) on accumulation of heavy metals showed that, because the whole socioeconomic development was in the first stage in Chengdu Plain at the beginning of 1980s, the major factors which influenced first section and third section were socioeconomic development level, and ones which influenced second section was the factor of socioeconomic rate. However, there was an obvious change in 2002. As far as first section which had better economics, agricultures and urbanization was concerned, the major factors were indirect pollution input, major socioeconomic production value, soil agricultural environment and so on. As far as second section which had better economic development and ecological environment was concerned, the major factors were indirect pollution input and rural conditions. The accumulation of heavy metals in the third section was lower than the whole study area. The third section which had unbalanced level of socioeconomic development and better ecological environment was influenced slightly by indirect pollution input and socioeconomic rate.There were 11 index acquired by the superior capability and momentum of BP network. These index were non-agricultural population proportion, average GDP, growth rate of GDP, industrial output value above a certain scale, passenger-kilometers by year, freight ton-kilometers by year, average cultivated area, yield of grains per hectare, multiple crop index, output value of agricultureper hectare and discharge of waste water by industrial enterprises. Three layers of BP network were established. There were 11 imports, 1 export and 1 hidden layer. Activation function in hidden layer presented as "S" and was liner function in export layer. Expectation error was 0.02. The most training frequencies were 8000. Initial value of learning rate was 0.01.Compared target vector of training samples with simulated export value and verified fitting extent of network model after network training, the simulated values in a variety of heavy metals were near to measured values .Meanwhile, average fitting errors of model were 0.4% below and fitting precision were 99.6% above, which verified fitting extent of BP network was very high. Compared BP network with the method of traditional regression, the former had higher precision about prediction of heavy metal content in soil. The extent of average precision was between 78% and 83%, while the extent of average precision of regression was only between 68% and 74%. Therefore, model of BP network had superiority.Predicted values of influenced factors in 2005 and in 2010 were regarded as input of network and merged with the former samples then retraining it. Through this work, the weight values of network were updated to acquire predicted values of Xindu in 2005 and in 2010. Predicted values for reference were acquired after integrative manage. 5. Analysis of spatial variability of soil heavy metal forms and driving factorsUsing geostatistical method to analyze the spatial structure of soil heavy metal can reflect random, structure, independence and relativity of all kinds of soil heavy metal, and reflect its changeable characteristics further in details. Grey correlated analysis, which was based on the relation analysis between soil heavy metal forms and soil physical and chemical characteristics, can open out the main inner factors which drive soil heavy metal changing (physical and chemical characteristics).The description statistic of the content of different forms (exchangeable, bound to carbonate, bound to Iron and Manganese, bound to organic matter, residue) of heavy metals showed, except Cd in soil was priority to bound to Iron and Manganese oxides, and the average content was 0.086mg/kg, which accounted for 32.21%, the rest four elements, Cu , Pb, Cr, Zn gives priority to residue form, and the average content was 26.96mg/kg, 39.63 mg/kg, 98.63 mg/kg and 67.84 mg/kg, accounting for 75.92%, 59.11%, 92.63%, 72.16% of total content. The orders of different forms of five elements were, bound to Iron and Manganese oxides > residue form > bound to carbonate > bound to organic matter form > exchangeable form for Cd, residue form > bound to organic matter > bound to Iron and Manganese > bound to carbonate > exchangeable form for Cu, residue form > bound toorganic matter > bound to iron and manganese > bound to carbonate > exchangeable form for Pb, residue form > bound to organic matter > bound to iron and manganese > bound to carbonate > exchangeable form for Cr, residue form > bound to organic matter > bound to iron and manganese > bound to carbonate > exchangeable form for Zn. At the same time, the proportion of activity form in total content of five elements was quite different. The content of active Cd was 0.194 mg/kg accounting for 72.66%, which was the highest proportion in total content. The content of active Pb was 27.41 mg/kg, accounting for 40.89% which was the second proportion in total content. The content of active Zn and Cu were 26.17mg/kg and 8.55mg/kg accounting for 27.84% 24.08%, which was the third proportion in total content. The content of active Cr was 7.83mg/kg accounting for 737%, which was the last proportion in total content. The result indicated that Cd had the highest activity and Cr had the lowest activity. In addition, the changes of coefficients of variation among five forms for Cd and Cu were relatively large. All kinds of soil Cd changed distinctly, and the range of coefficient of variation was 43%~123%, which of bound to carbonate was the biggest 122.64%. The coefficient of variation of every form of heavy metal Cu was big; the biggest was bound to Iron and Manganese (103.23%). And it belonged to intension variation; the others belonged to middle variation. The range of coefficient of variation of different forms for the rest three elements was 25%~75%, which accorded with moderate variance.The analysis of spatial structure variability and inner factors (soil physic and chemic properties) showed that, bound to organic matter Cd had spatial autocorrelation, its structural factors affecting Cd accounted for 81.2%, and there was bigger variation mainly at southeast-northwest (135° direction). The main influencing factors were coarse silt, pH and organic matters. The rest forms had middling relativity, mainly happened at southwest and northeast (45° direction). The results of analyzing the inner factors indicated that major factors influenced exchangeable Cd, bound to carbonate Cd, bound to Iron and Manganese oxides Cd and active Cd were pH, bulk density and medium fine silt. The variability of exchangeable Cu was intensity spatial autocorrelation, and the other was moderate. The direction of spatial variability of every form mainly represented 45° and 135°. The inner factor of impacting the content of exchangeable Cu was organic matters, and impacting the content of organic combining conditions Cu was clay, sand and organic matters. Soil clay and organic matters affected the content of active Cu in greater extent, but the relationship between bound to carbonate and bound to Iron and Manganese form did not. Bound to carbonate, bound to organic matter form and active Pb were intensity spatial relativity-self in short distance, exchangeable form and bound to Iron and Manganese form were moderate spatial relativity-self inlonger distance. The variance mainly showed in the direction of northeast and southwest (135°), next in the direction of southeast and northwest (45°). Soil pH obviously influenced the distribution of exchangeable form and bound to carbonate content, and soil organic matter also influenced the distribution of bound to carbonate content. The main factors, which influenced the content of bound to Iron and Manganese form were soil organic matter and pH. The main factor, which influenced the content of active Pb was soil organic matter. The main factors, which influenced the content of bound to organic matter Pb were soil organic matter, clay, CEC and sand. All forms of Cr had intensity spatial relativity-self except for exchangeable form and active form, which had moderate spatial relativity-self. The relativity analysis between soil physical, chemical characteristics and content of different forms of Cr showed that, soil clay had notable positive relativity with bound to carbonate, bound to Iron and Manganese and bound to organic matter form. Bound to organic matter form and active form also had notable positive relativity with soil organic matter; CEC was the main factor, which influenced the content of active Cr. All forms of Zn had intensity spatial relativity-self except for exchangeable form, which had moderate spatial relativity-self. pH mainly influenced exchangeable form, bound to carbonate and bound to Iron and Manganese. Organic matter was the main factor, which influence the content of various form of Zn except exchangeable Zn. There were many factors, which influenced the content of bound to Iron and Manganese, such as clay, medium fine silt, sand and CEC, except for pH and organic matter. The main factors which influenced the active Zn were clay, sand, organic matter and CEC.The spatial interpolation analysis of different forms for five elements showed that, the higher area of Cd content mainly distributed in the north, northeast Deyang and Pengzhou district, and the lower area mainly distributed in Wenjiang, Chongzhou, and Qionglai et al, except for bound to organic matter Cd. The highest value region of exchangeable form, bound to carbonate and bound to Iron and Manganese content mainly existed in the north of Chongzhou, Pengzhou, which was distributed in the northwest of study area, and in the southeast of Shuangliu, suburb of Chengdu and Xindu, and in some parts of Deyang. The distribution trend of bound to organic matter form and active Cu content was the same with the three forms in front except was lower in northeast Deyang. The distribution of exchangeable form and bound to carbonate content appeared as strip belts or gobbets, the highest value belts mainly existed in northwest Dujiangyan and northeast Deyang. The distribution of bound to Iron and Manganese, bound to organic matter form and active form content appeared as strip belt, the highest value belts of bound to Iron and Manganese mainly existed in Chongzhou and Xinjin. The highest value belts of bound to organic matter form and active formcontent existed in north Pengzhou, northwest Dujiangyan and north Shuangliu and Xinjin. The distribution trends of content of various forms for Cr were different, but all had the characteristics that lower in the middle of the plain close to west, higher in the north region. The spatial variability of various forms of Zn mainly indicated in the direction of 45°, the highest value belt most existed in north Pengzhou, Chongzhou, and some parts of Deyang. 6. The environment effect of various forms of soil heavy metalBased on comparing the different cumulating degree of heavy metal in various kinds of crops, this paper discussed the accumulated relationship between heavy metal forms and different crops by correlated and grey correlated analysis. Simultaneously, recurred to the relationship between variation of heavy metal form and mainly physical and chemical properties, thorough analyzing the main heavy metal form which can affect the validity of heavy metal and the mainly physical and chemical properties which can aroused variation, then introduced a standard of soil environment quality.The statistic of the content of heavy metals in different corps had been done by applying Nation Foodstuff Sanitation Standard. The result showed that, the content of the Pb, Cd> Cr and Cu expect Zn was all exceeded the standard in wheat. There were 8 samples of the Pb in wheat were exceed, The exceeding point was 17.4%, which was distributed in Deyang and Chongzhou, and the maximal superscale was 0.76 times. But there were 4 samples of them only exceeded smally, the superscale ratio was just only 10%. For the rice, there was only Pb and Cd content exceeding the standard. Among them the content of Pb had 5 samples exceeding the standard, the ratio of exceed point was 10.90%, the average and the maximal exceed times were 0.38 and 0.69, respectively. For the Cd, there are 4 samples' content is exceed, it is 8.7% of the total samples, which are located in Deyang. For the Cr, Cu, Zn, their content are all not exceed. In the rapeseed, the content of Pb, Cd, Cr and Cu except Zn are all slightly exceed. And the maximal one is Cr which is exceed 10.42% By the accumulated rate, the order of the different heavy metals among the rice, wheat and rapeseed is Cd> Zn> Cu> Pb> Cr. The accumulated order for the wheat, cole and rice among the Cr , Pb , Zn and Cd is :wheat> cole > rice; wheat>rice>cole; cole>wheat>rice and cole>rice>wheat, respectively.The relation between the different crop varieties and the content of the heavy metal and its form indicated that, the content of the Cd in wheat had significant positive correlative relation to its form which contains exchangeable, bound to carbonate and the oxidation of Fe and Mn. The content of Zn had significant positive correlative relation to soil exchangeable Zn and the organic combine form; The Cr and Cu just only had a significant positive correlative relation to its exchangeable form in...
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