Abstract
The parental material of soils in the Qilian Mountains of northwest China is mainly aeolian loess containing CaCO3 which may remain in soils under the semiarid-arid climate. To disclose the CaCO3 characteristics change with the altitude and the terrain attributes, we surveyed 18 soil profiles in an altitude sequence from 3076 m to 4510 m in the Hulugou Watershed in the Qilian Mountains, measured CaCO3 contents of all genetic horizon samples, analyzed the densities, illuviation modes and depths of CaCO3 in the profiles, extracted values of the terrain attributes of the profiles including altitude slope, aspect, plane curvature, profile curvature and terrain wetness index (TWI) from the 90 m resolution SRTM3 DEM data on ArcGIS 9.3 platform. We found that CaCO3 weighted content of the profiles ranged from 1.30 g·kg-1 to 93.09 g·kg-1, CaCO3 density from 0.05 kg/m2 to 75.69 kg/m2, CaCO3 illuviation depth from 12 cm to 54 cm. CaCO3 illuviation modes could be divided into three types, i.e., no illuviation mode in which the profile has only A horizon or CaCO3 content -1, middle illuviation mode in which CaCO3 accumulated in a middle horizon, and down illuviation mode in which CaCO3 content increases with the depth. CaCO3 weighted content, density and illuviation depth had significant correlation with certain terrain attributes. In general, the altitude sequence is an effective way to study CaCO3 characteristics in the alpine region, and the data of terrain attributes which can influence the precipitation and its redistribution in soil are potential in predicting soil CaCO3 characteristics in the alpine region.
Highlights
The Qilian Mountains is located in the northeast fringe of Tibetan Plateau of northwest China
Results of Curve Estimation between Profile Thickness (PT), GV(%), Bulk Density (BD) and terrain attributes were presented in Table 3, which indicated that altitude, gradient and aspect can be used to predict the PT, GV(%) and BD, while altitude had a higher prediction efficiency in comparison with gradient and aspect
These 18 profiles can be categorized into three kinds of illuviation modes of CaCO3 according to CaCO3 contents of different horizons (Figure 2): 1) No illuviation mode, for examples of the profiles above 3600 m in altitude only had one horizon (P1 to P7) or profiles where CaCO3 leached out intensively from the soil (
Summary
The Qilian Mountains is located in the northeast fringe of Tibetan Plateau of northwest China. It is the important source of water for the famous Hexi Green Corridor, one of the most important agricultural regions in northwest China. A lot of soil information in altitude sequence is available in the Qilian Mountains, for example, soil organic matter, total nitrogen, water retention and microbe [1] [29] [30] [31] [32], but little reference is found on soil CaCO3 there. This paper mainly aims at: 1) select a typical watershed in the Qilian Mountains; 2) survey and sample typical soil profiles in an altitude sequence; 3) disclose CaCO3 content, density, illuviation mode and depth of CaCO3, and their relation with the terrain attributes
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