Abiotic soil crust formation on dunes in an etremely arid environment: A 43-year sequential study

The spatial and temporal patterns of soil crust formation on stabilized dunes at Shapotou, northwestern China, were studied on a time sequence of 0, 18, 35, and 43 years. The spatial pattern of soil formation was estimated by measuring the thickness of accumulated sand fractions on the stabilized dune surface and by analyzing the particle size distribution of soil crust. The results showed that the materials forming the embryonic crusts did not come entirely from atmospheric dustfall, but more likely originated from the deflation process of shifting sand and were related to the characteristics of shifting sand particles. Irrespective of the age, all crusts contained a relatively large proportion of 0.01-0.05 mm particles, suggesting that the 0.01-0.05 mm particles provide a material basis and are a prerequisite to the formation of soil crusts. The formation of crust was a sorting and accumulation process of 0.01-0.05 mm particles. Simultaneously, the formation of stable soil crust apparently tended to be subjected to aggregation processes that include aggregation of inorganic particles themselves and aggregation of organic and inorganic particles. The soil crust was in a constantly alternating process of formation and disruption. The alternation period was about one year. Through this alternation, the fine soil layer beneath the crust can be continuously widened and thickened with increasing stabilization time.