Geochemical barriers and element retention in soils in different landscapes of the Tianshan Mountain area, Xinjiang, China

Geochemical barriers (GBs) are defined as a local epigenetic zone where the conditions of elemental migration are distinctly altered, resulting in a substantial accumulation of selected elements. It is of great importance to understand the local distribution pattern of elements and their availability affected by local factors. A soil survey of two predominant landscapes, an arid desert landscape and an alto-cryic landscape, in the Tianshan Mountain area, China was conducted to study GBsʹ types, characteristics and distribution in the area, and distribution of selected elements and their availability within the GBs. In the Tianshan Mountain area, there were mainly mechanical and evaporative GBs in the arid desert landscapes and biological GBs in the alto-cryic landscape. Mechanical GBs influenced by the change of water-or atmosphere-flow velocity were distributed along piedmonts or in depressions away from the mountains, and characterized by an accumulation of clay accompanied with Ba, F, K, Li and Zn as well as highly available Fe, Cu and Zn in soil pedons. Distributed from mountain to the basins on both sides of the mountains, evaporative GBs appeared with a sequence of calcium carbonate (CaCO3), gypsum and soluble salt evaporative GBs, corresponding to the variation from moist to dry microclimate conditions. Besides saline materials, these GBs possessed an accumulation of available F, total B and Sr, and total and available B in CaCO3, gypsum and soluble salt evaporative GB, respectively. The dominant majority of biological GBs was in the alto-cryic landscapes of the mountains, where cold and wet climatic conditions caused organic matter to substantially accumulate in the topsoil. The availability of Cu, Fe and Zn was significantly increased in the biological GBs, and the availability of F, however, decreased. Understanding of these characteristics may be beneficial for sustainable agriculture, human health and the protection of vulnerable arid environment.