Content, Density, Illuviation Mode and Depth of CaCO₃ in Soils of Semiarid-Arid Qilian Mountains—An Altitude Sequence Study of the Hulugou Watershed

Abstract

The parental material of soils in the Qilian Mountains of northwest China is mainly aeolian loess containing CaCO 3 which may remain in soils under the semiarid-arid climate. To disclose the CaCO 3 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 CaCO 3 contents of all genetic horizon samples, analyzed the densities, illuviation modes and depths of CaCO 3 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 CaCO 3 weighted content of the profiles ranged from 1.30 g·kg -1 to 93.09 g·kg -1 , CaCO 3 density from 0.05 kg/m 2 to 75.69 kg/m 2 , CaCO3 illuviation depth from 12 cm to 54 cm. CaCO 3 illuviation modes could be divided into three types, i.e. , no illuviation mode in which the profile has only A horizon or CaCO 3 content < 5 g·kg -1 , middle illuviation mode in which CaCO 3 accumulated in a middle horizon, and down illuviation mode in which CaCO 3 content increases with the depth. CaCO 3 weighted content, density and illuviation depth had significant correlation with certain terrain attributes. In general, the altitude sequence is an effective way to study CaCO 3 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 CaCO 3 characteristics in the alpine region.