三峡库区不同地貌区土壤元素分布特征

The Element Distribution Characteristics of Soils in Different Topography in the Three Gorge Reservoir

利用土壤表层样分析成果,探讨三峡库区不同地貌区土壤中Ca、P、B等4 3个常量元素及微量元素的分布特征,结果表明:三峡库区重庆段八个地貌分区可明显划分为两个地球化学分区,一区为河谷平原、侵蚀剥蚀台地、丘陵、低山及中山地貌地球化学分区;二区为褶皱抬升低山、中山及喀斯特地貌地球化学分区,两区的土壤元素含量差异明显,除常量元素K2 O、SiO2 、Ba、MgO、P、Zr及微量元素Sr、La外,一区土壤中其他元素含量总体上均远低于二区土壤中的含量,其差异总体上是地质背景差异的体现,母岩岩性是土壤元素的主要控制因素。在同类母岩条件下,地貌对土壤中元素分布具有明显影响。不同地貌区的土壤营养元素聚类既有共性也有个性,喀斯特地貌区元素聚为五类;褶皱抬升中山、低山区聚类结果基本一致,均为四类;侵蚀剥蚀中山区多数元素较分散,分异强烈,总体上聚为四类,但第四类各元素间距离较远;侵蚀剥蚀低山与丘陵区元素聚类总体上相近,均为五类,但内部存在分异;侵蚀剥蚀台地则聚为三大类。土壤中的某些特征矿物元素如Fe2 O3 、Mn、Cu、Zn组合,N、org C组合在各个地貌区均聚为一类;而某些元素如Cl等在不同地貌条件下分别与MgO、CaO或与Na2 O聚类。

According to the analysis results of topsoil, the distribution characteristics of main elements and trace elements, including Ca, P, and B, etc. in soils from different topography in the area of the Three Gorge Reservoir have been discussed. The results show that two geo-chemical districts can be divided in the Chongqing area of Three Gorge Reservoir. One is the river valley plain and erode denudation topography district, another is fold uplift and karst topography district. The element contents in soils from two districts have different characteristics. Except the main element K_2O, SiO_2, Ba, MgO, P and Zr and trace element Sr and La, the contents of other elements in the first district is much lesser than those of the second district. These characteristics are determined by the diversity of the geological background. The element distribution of the soils, forming from same kinds of parent rocks ,is influenced by the types of topography. From the valley plains to erosion plateaus and hills, the parent rocks are the mudstones and sandstones mostly, so the contents of B and Bi etc are almost alike in different topography section. When the elevation rises, the contents of Ca, Pb, Zn and La etc decrease, and Se, I and Nb increase. Except SiO_2, Zr, Nb, Se, I, Br, W, and As, the main elements and trace elements in mid-mountain of erode and denudation type are lower than that of other topographies. The soil and water loss is responsible for lower contents of elements in this area. When some elements, such as CaO, Cu, Y, and Cl, transfer from high topography to lower topography they behave the jump change characteristics. The clustering of elements in soils according to the different topography, show the various features. The elements, such as Fe_2O_3, Mn, Cu, and Zn group or N and org.C group cluster in the same kind in different topography. But some element, such as Cl, cluster with MgO and CaO or Na_2O in terms of the topographical condition, showing the assembled characteristics of elements vary in various topography.