Erodibility of some crust forming soils/sediments from the Southern Aral Sea Basin as determined in a wind tunnel

Severe dust storms Southern Aral Sea Basin have bcome common with the desiccation of the sea. The high incidence of dust in the area has had severe ecological consequnces. Within the frmewoek of efforts to reduce this phenomenon, deflatability as well as deflatabillity-related characteristics of some prominent soils/sediment surfaces in the Southern aral Sea Basin were examined. The materials included as a salt crust from a developed Solonchak, a Takyr crust and a Takyr-like soil, and salt crust from undeveloped Solonchaks formed on the exposed bottom of the Aral Sea. Characteristics determined were particle size ddistribution, dry aggregate size distribution and sat, carbonate and organic carbon contents. Deflatability was examined using a suction type wind tunnel with a SENSIT-type sensor to detect airborne unconsolidated material, on materials treated to different moisture levels and with a chemical stabilizer, and on restored crusts created from the unconsolidated materials. Fine sand dominates in the materials, and in the Takyr crust and Takyr-like soils is accompanied by significant amounts of silt and clay. All materials contain moderate amounts of carbonate and are low in organic matter. All soils/sediments contain salts, but in the salt crusts of the Solonchaks the salt fraction dominates. They all have more than 50 per cent PM₈₅₀ (particles with diameter <850 μm), indicating a relatively high deflatability potential. The materials from the Takyr crusts and Takyr-like soil with a high proportion of fine aggregates had the lowest threshold friction velocities, while the salt crusts of Solonchaks with a high proportion of coarse aggregates had the highest. This suggests that Solonchaks and Takyr-like soils are the most deflatable and Solonchak soils the least deflatable. These differences are attributed to the presence of salts that create stable, large aggregates in the Solonchak crusts. Wetting of the materials to three moisture levels considerably increased threshold friction velocity. The increase was most prominent in the sat-rich materials, and was attributed to the rapid formation of surface films by dying in the course of the wind tunnel determinations. Applications of chemical stabilizers at two levels also considerably increased threshold friction velocity. On the restored crust, threshold friction velocity dramatically increased, occasionally to non-recordable values. This increase was monitored with both the salt crusts characteristic for the Solonchak soils and the fine-grained crusts characteristic for the Takyr soils. The stability was attributed to the tightly packed salt particles in the salt crusts, and to the cohesive properties of the fine-grained materials in the Takyr crusts. Once the crusts were ruptured, however, strong deflation commenced. These results suggest that by maintaining moisture in the soil/sediments (for example, by maintaining a high water table in the Amu-Darya river flood plain) deflation can be reduced. By the same means, deflation can be reduced by creating new crusts or by preserving existing crusts.