汾河源区不同景观带表土粒度与地球化学元素组成分析

基于ArcGIS，将汾河源区景观带谱分为亚高山草甸带、针阔叶林带、灌丛荒草带和河流两岸农田耕作带等4个类型，并对不同景观带表土沉积粒度和地球化学元素进行了初步分析。结果表明汾河源区表土沉积物以粉砂为主，辅以一定数量的极细砂和粘土，细砂和中粗砂含量较低；总体上沉积物分选差，呈正偏和极正偏的分布，峰态中等到尖窄；沉积物沉积环境复杂多样，风成、海相/河流沉积并存，与区域地质构造运动、风成物质堆积和河流发育有着密切的关系。地球化学元素分析发现该区表土沉积以SiO₂、Al₂O₃、Fe₂O₃为主，与上部陆壳（UCC）和中国黄土（CL）相比具有显著的同源性；而Ca和Mg等活动性元素则随海拔高度影响的降水变化呈现明显的垂向差异；沉积物化学风化基本处于脱Ca和Na的初级阶段，属寒冷干燥条件下的低等化学风化。研究旨在揭示沉积物粒度特征和地球化学行为，为进一步认识汾河源区生态环境变化提供理论基础和数据支撑。

Topsoil particle size and geochemical elements in the different landscape zone in Fenhe River headwater catchment

With the support of ArcGIS remote sensing image, this paper classified the landscape belts of Fenhe River headwater catchment, Shanxi Province, China into four categories including subalpine meadow belt, coniferous and deciduous forest belt, bush and grass belt and farming land belt at both shores of the river. The samples of the surface soil (0-10 cm)in different landscape belts were collected from September to October, 2012, and then preliminary analysis of its superficial deposit granularity and geochemical elements were conducted. Granularity analysis was completed through applying the Mastersizer 2000 type laser particle analyzer produced by UK Malvern Company. Specifically, 10% H₂O₂ was added to remove the organic matter and dissolvable salt; 10% HCl was added to exclude carbonate; and then distilled water was filled to keep still for over 12 h. Subsequently, the 10% sodium hexametaphosphate was put in Ultrasonic oscillators to be tested after it was fully scattered. The results prove the test error is less than 0.2%. The geochemical elements were tested as follows:firstly, the air-dried samples must be milled into below 200 meshes, then 4 g was weighed and dried at 105℃ to be put in sample preparation mold for shaping into a round test sample with the external diameter of 32 mm, finally the sequential wavelength dispersion type of x-ray fluorescence spectrometer produced by PANalytical B.V. was applied as the test instrument, for its element test error was less than 5%. Results show that the superficial deposit of Fenhe River headwater catchment is mainly composed by silt, supplemented by certain amount of extremely fine sand and clay, while the content of fine sand and medium-coarse sand is low. In general, the deposit separation is poor, showing a positively biased and extremely positively biased distribution with medium to sharp kurtosis. The deposition environment is complicated and diverse with the coexistence of eolian deposit, marine facies and fluvial deposit, which may be closely associated with the regional geological conformation movement, airborne material deposition and river development. From the analysis of geochemical elements, it is found that the superficial deposit of this area mainly contains SiO₂, Al₂O₃ and Fe₂O₃, showing significant homology with upper continental crust (UCC) and Chinese loess (CL). Active elements like Ca and Mg also present obvious vertical difference with the precipitation change influenced by altitude. The chemical weathering of the deposit basically lies in the preliminary stage of excluding Ca and Na, which belongs to the low level chemical weathering under cold and dry conditions. As the major ecological environment weak belt and environment sensitive reflection belt of the rivers sources, Fenhe River headwater catchment is taken as the typical area for exploring the current ecological environment deterioration and future environment evolution trend, which is of great academic and practical significance. As the basic link of such research, this study aims to provide theoretical basis and data support for further understanding the ecological environmental changes by utilizing the superficial deposit of different landscape belts in Fenhe River headwater catchment for preliminary granularity and geochemical analysis.