Background Values of Some Trace Elements of Soils in the Reservpir Area of the Yangtse Gorges
长江三峡库区部分元素土壤环境背景值研究

This paper reports on background values of some elements in soils of the reservoir area around the Yangtse Gorges. The sampling design was made like this: the said area was divided into eleven environmental units in accordance with environmental differences and in each unit, a certain amount-of sampling points were arranged according io intensity of impacts of natural and social environments upon soil system, resulting in 118 sampling points all told.Data processing was done like this: hypothesis testing of difference of mean values of two normal populations, or rather t-testing with pairing comparison was used to "analyse the data from surface layer and sub-surface layer of soil, and the result showed the difference between these two layers was insignificant, so the background values of soil were calculated with the surface layer data, and abnormal values were rejected by using the method of plus of minus three times of standard error with arithmetic mean value. In addition, the classification of concentration distribution was tested by Pilson X2 method, Shapro-Wilk W method, Kolmogrov method, Skewness and Kurtosis method. In soil of the whole area, Pb, Zn and As were subjected to normal distribution, Cu logarithmic normal, and Ni skew normal, Variables subjected to normal distribution were represented by arithmetic mean plus or minus standard error. Variable subjected to logrithmic normal distribution was represented by geometric mean multipling or dividing standard error. Variables subjected to skew normal distribution were processed by normalization. The result of conputation gave the background values of soils in the reservoir area: Pb was 20.15±6.47ppm, Cu 13,76±2.06ppm, Ni 22.64±7.57ppm, Zn 78.27±20.42ppm, and As 9.09±4.45 ppm. Then, the variance analysis and Duncan method of multi-comparison were used to testing the differences of background values of soil environment between different soil groups and that between different parent materials respectively. Besides, analysis for the causes of the differences was processed. The conclusion is that difference between different soil groups was caused by different conditions of water, heat, biology and parent materials, and the function of irrigation-plowing cultivating as well, while the differences between different parent materials had relations with the palaeogeographic environment in which the parent materials of soils were transformed into rocks.