Properties and periglacial processes in alpine meadow soils, western Nyainqentanglha Mountains, Tibet

One hundred and three samples were collected from nine soil profiles in alpine meadows on glacial moraines in two valleys on the northwestern slope of the West Nyainqentanglha Mountains, central Tibet. Properties measured were soil organic carbon (SOC), soil organic matter (SOM), principal anions and cations, total nitrogen, available nitrogen, pH, water content and grain size. High concentrations of SO42−, HCO3− and Cl− and lack of CO32− are consistent with the acidity of the soil: pH < 6.21. Na+ and K+ are concentrated at depths of 0.2–0.4 m. A high concentration of Ca2+ in the profiles indicates that leaching is weak. Sand and pebbles are dominant in soils with low clay content. These characteristics all indicate that the soil, which began to form in late Holocene time, is not well developed. The SOM and SOC contents are closely correlated and decrease with depth. Thus, SOM determined by the simple and quick loss on ignition method (LOI) can be substituted for SOC determined by the time-consuming and expensive Walkley-Black method (WB). Both SOM and SOC decrease with depth, but in contrast to a commonly reported result, their ratio, SOM/SOC, does not increase with depth in some of our profiles. This is attributed to periglacial processes that prevent organic matter with oxygen-functional groups from moving downward in the soil profiles. Periglacial processes may also disturb the soil layers through gelifluction. Consequently organic carbon does not decrease with depth in the profiles as it commonly does in low altitude areas. This is potentially significant in understanding the degradation and development of landforms in Tibetan landscape.