No abstract

Despite the importance of desert dust at global and regional scales, its exact provenance is often unclear. The Taklimakan Desert in northwest China is a common source of high‐frequency regional dust storms and is also a large source of global dust production. On the basis of field observations and the determination of the fraction of aeolian dust in surface samples, we characterized the relative intensity of windblown sand/dust processes in the Taklimakan and the volume of dust emitted (PM10) during these processes. Major dust sources were degraded lands on the eastern desert margin, the Gobi and alluvial, fluvial and aeolian sediments occurring on the desert margin. These areas have high PM10 emission capacity due to high‐surface PM10 concentrations and intensive windblown sand/dust activity. Despite having intensive windblown sand activity, the central desert had lower PM10 dust emission capacity (<1·6 kg day−1 m−2 in spring, <0·08 kg day−1 m−2 in other seasons) due to lower surface PM10 fraction. The dry Taitema Lake bed was a source of potentially high dust emissions (at least 4·4–17 kg day−1 m−2 for the monitoring period) due to the intensity windblown sand/dust activities, despite low PM10 concentrations. The dry river beds on the southeastern desert margin had lower dust emission potential due to low PM10 concentrations and windblown sand/dust activity. Most dust emission sources lie in the paths of prevailing winds, leading to aeolian dust transported to and deposited in the desert hinterland or Hotan, Yutian and Minfeng areas, where wind stream convergence leads to high‐frequency dust storms. Copyright © 2011 John Wiley & Sons, Ltd.

Abstract. Rivers flow across aeolian dunes and develop braided stream channels. Both aeolian and fluvial sediment supplies regulate sediment transport and deposition in such cross-dune braided rivers. Here we show a significant selective deposition in response to both aeolian and fluvial sediment supplies in the Ulan Buh desert braided channel. The Ulan Buh desert is the main coarse sediment source for this desert braided channel, and the mean percentage of the coarser ( > 0.08 mm) grains on the aeolian dunes surface is 95.34 %. The lateral selective deposition process is developed by the interaction between the flows and the aeolian-fluvial sediment supplies, causing the coarser sediments (> 0.08 mm) from aeolian sand supply and bank erosion to accumulate in the channel centre and the finer fluvial sediments (< 0.08 mm) to be deposited on the bar and floodplain surfaces, forming a coarser-grained thalweg bed bounded by finer-grained floodplain surfaces. This lateral selective deposition reduces the downstream sediment transport and is a primary reason for the formation of an "aboveground" river in the braided reach of the upper Yellow River in response to aeolian and fluvial sediment supplies.