| At present the regional agricultural environmental deterioration in our country and the heavy metal pollution of agricultural products are rather serious, especially in economically advanced regions. Therefore heavy metal pollution is the key point and difficulty in agricultural environmental research and protection. According to Agricultural Department Environment Monitoring System's research in recent years, in the 320 seriously polluted areas in regions with faster economic development, including the suburbs of 24 provinces and cities in our country, regions of polluted water bodies, factories and mining mountains, etc, the farm produce planting areas with crop pollution beyond the standard value occupy 606.000 hm~2, which account for 20% of the total areas of the monitoring research. In these polluted areas, the yield and area of farm products in which the content of heavy metals exceeds standard account for about over 80% of the gross yield and total area of farm products that have excessive contaminants, especially Pb, Cd, Hg, Cu pollution and their composite pollution, which are the most prominent. Chongqing is the key city in southwest China and one of the old industrial base stations, where finite soil resource is continuously affected and polluted due to the long-time industrial development. Among all the contaminants, the pollution of heavy metals is characterized by irreversibility, lastingness and severity, and not easy to be eliminated, which arouses special attention of the society.Geostatistics was first applied in the reconnaissance and calculation of mineral deposit of the mining industry in South Africa in the 50s. On the ground of numerous fundamental theory researches, in the 60s, the famous French statistician Matheron G put forward The Theory of Regionalized Variable, which formed the basic frame of Geo-statistics. Through the development over 30 years, geo-statistics has been widely applied in many fields that require the evaluation of space and time variation. Geo-statistics, which can retain information of space variation to the maximum, is a robust tool to research space variation. With regionalized variable as its kernel and theory base, the method is a kind of mathematical geological method using spatial correlation and variation functions as its basic tools. Now the application of geo-statistics in Geology for Mineral resource has been mature, and it also has been widely used in many other fields such as hydrology, agrology, etc. The pollution of heavy metals in the soil is an urgent issue that pedologists must cope with. Kriging interpolation offers a method which provides a non-deviation best estimator for predicting the soil specialty. Therefore, more and more researchers begin to use geo-statistics to Kriging interpolate and chalk out the soil polluted by heavy metals.This paper studies the specimens of soil from arable areas in 39 counties and towns throughout the city of Chongqing. 455 portions of soil specimens are achieved to analyze and gain the result of theeight heavy metals such as Hg, As, Cr, Cd, Cu, Zn, Ni, Pb. With the help of GIS, applying Geostatistic theory, the research studies the space variation of the eight heavy metals in the soil on farmlands, and predicts the content of their distributions in arable areas in Chongqing. The main research contents and results are as follows:(1) As for the content distribution of the eight heavy metals in Chongqing's arable lands, with the exception of Cr taking on normal distribution, the other seven show logarithm normal distribution, so the statistics of the content of Cr in the soil should use arithmetic mean value and standard deviation as the typical value, while the other seven elements use geometric mean and standard deviation as the typical value. The range and average of the content of certain kinds of heavy metals are as follows: Hg 0.017~0.546(0.076), As 0.232~272.513(8.094), Cd 0.040— 19.105(0.364), Cr 15.920 - 161.988(53.802), Cu 0.850 ~ 345.250(19.648), Zn 29.075 ~ 751.625(95.131), Ni 2.840~ 183.100(29.061), Pb 7.425—309.175(52.089) mg/kg soil. Other than Cr, Cu, Ni. Five heavy metals, Hg, Cd, As, Pb, Zn, exist with a phenomenon of obvious accumulation. Compared with the normal soil worldwide, in Chongqing's soil the content of Hg, Cd, As, Pb, Zn is above average. Cr, Ni below average and Cu approaching,(2) In Chongqing's arable lands the heavy metals are highly correlated such as Cd—As, Cu—As, Zn—As, Cd—Cu, Cd—Zn, Cu—Zn, Zn—Pb, which indicates that there is a higher homology between them. Pb and As, Cd, Cu. Cr and Ni also have some consanguinity. Hg has the lowest relativity with other elements, which indicates that it is unique in accumulation. In the soil Cr accumulates insufficiently from outer fountain, which has a lower relativity with other elements as well. Data shows that Cd, As,Cu are the three elements that accompany pollution most frequently.(3 ) The spatial variation regulation of the heavy metals in arable soil in the city of Chongqing is as follows:The ratio of nugget value to sill value is [C0/(C+C0)] Cu>Pb>Ni>As>Cr>Hg>Cd>Zn. As the ratio of nugget value to sill value reaches 86.59% and 76.84% respectively, Cu and Pb belong to low correlation in space. As for the other six elements, with the ratio of nugget value to sill value ranging from 25% to 75%, they belong to median correlation in space. The space correlativity is the result of the structural factor and random factor common effect. The structural factor refers to the mother soil, the type of soil, the weather, etc, and the random factor to plowing, arrangement, cultivation system, pollution and other man-made activities. Cr belongs to the median space correlativity, however its sill value reaches 170.662, and the ratio of semi-variance variation resulting from the structural factors outweighs the one resulting from the random factors, which prove that the content of Cr in the soil is relatively affected by the factor of forming the soil. Their range shows that different elements differ in their own space and relative range (space), except for Hg,Cd and Cu being the... |
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