Effects of efflorescence and subflorescence by different salts on soil physical properties and aeolian erosion

Abstract

Salt minerals have profound influences on soil architecture and physical properties through efflorescence and subflorescence. However, there is a lack of data on identifying the role of salt mineral types in aeolian erosion. In this study, seven types of single salt including NaCl, KCl, MgCl2, Na2SO4, K2SO4, MgSO4, and Na2CO3 were examined to preliminarily explore the influencing mechanism of efflorescence and subflorescence by these salts on aeolian erosion. Soil samples treated by these salts were prepared under an environmental condition of summer in the semiarid region and wind tunnel tests were conducted subsequently under a strong wind of 18 m s−1. The results show that Na2SO4, MgSO4, and Na2CO3 generated highly emissive surfaces. Crystals of Na2SO4 and Na2CO3 occurring in an acicular form and arranging loosely induced crusts with weak strength. For MgSO4, the fluffy aggregates on the crust surface as a result of dehydration were the main dust source. MgSO4 crystals within the crust occurred in a prismatic form and were covered with fissures or cracks, inducing a salt crust with great strength, but having the tendency to dehydrate. The crystals of NaCl, KCl, and MgCl2 occurred in cubic or tabular form and in compact arrangement, forming crusts with great strength and inhibiting dust emission. K2SO4 formed a thin crust peeling off from the soil which is susceptible to aeolian erosion. Under the influence of subflorescence, Na2SO4, MgSO4, and Na2CO3 attenuated the strength of the soil through salt heaving, which increased the potential of aeolian erosion. In contrast, NaCl, KCl, MgCl2, and K2SO4 played a role as bonding agent and reduced the potential of aeolian erosion. These results suggest that salts that could crystalize into hydrous and anhydrous minerals, such as Na2SO4, MgSO4 and Na2CO3, can remarkably enhance the potential of dust emission at the soil surface and subsurface.