Soil development along primary succession sequences on moraines of Hailuogou Glacier, Gongga Mountain, Sichuan, China

Soil properties related to soil development were measured in six profiles over approximately 180 years of soil development on recessional moraines of the Hailuogou Glacier, Sichuan of southwestern China. It is hypothesized that soil development is strictly time-dependent. Field and laboratory work indicate that as soil develops from initially coarse gravel outwash, the properties undergo a progressive physical and chemical change such that there is a considerable profile differentiation between the youngest and the oldest soils. The pH is also highly stratified; it decreases with time from 8.5 to 4.2 in the upper mineral soil and increases with depth in all profiles. Accumulation of soil organic C and N increases with time but the rates of accumulation become slower with time. Within the investigated timespan, soil C and N accumulated to a considerable level of 3.5 and 0.6 kg/m2 respectively, with mean annual rates of 28 g/m2 for carbon and 3.5 g/m2 for nitrogen. The rapid accumulation of organic C and N accelerates the processes of soil formation, but the content of organic C and N did not reach a steady-state during the observed timespan. The accumulation of soil organic matter results in increased acid production and in the chemical weathering of minerals that promote formation and translocation of the clay fraction and leaching of carbonate; it is also directly responsible for development of soil properties such as cation exchange capacity (CEC), and bulk density.