SAND DUNES AS POTENTIAL SOURCES OF DUST IN NORTHERN CHINA

Sand dunes are not typically considered large sources of desert dust. While saltation bombardment of sand grains on a fine substrate can produce considerable dust, the well-sorted nature of dunes themselves tends to preclude them as major dust sources. Recent research, however, has revealed sand dunes can, in some cases, be large sources of dust. We used the PI-SWERL (Portable in situ Wind Erosion Lab) to measure the potential of sand dunes to emit particulate matter <10 µm (PM-10) dust in the Tengger and Mu Us deserts of northern China. Combined with high resolution particle size measurements of the dune sand, an assessment of sand dunes as a dust source can be made. Large active linear dunes tend to contain little to no stored PM-10, yet they produce a low dust flux. Coppice dunes, or others stabilized by vegetation, contain appreciable PM-10 (probably dust deposited on the dunes) and have very high dust emission potential. There is a linear correlation between the amount of PM-10 stored in a dune and its potential dust flux. Saltation liberates loose fines stored in dunes, making them very efficient dust emitters compared to landforms where dust particles are unavailable for aeolian transport due to protective crusts or sediment cohesion. In cases where large dunes do not apparently store PM-10 yet emit dust when active, two hypotheses can be considered: 1) iron-oxide grain coatings are removed during saltation, creating dust, and 2) sand grains collide during saltation, abrading grains to create dust. Observations reveal that iron oxide coatings are present on some dune sands. Alternatively, our data suggests that low dust fluxes from dunes containing no stored dust may represent an estimate for the maximum amount of dust produced by sand abrasion. In addition, PI-SWERL results suggest that dust-bearing coppice dunes, which cover vast areas of China’s sandy deserts, may become major sources of dust in the future if overgrazing, depletion of groundwater, or drought destabilizes the vegetation that now partially covers these dunes.