The response of dune morphological transformation and sedimentological reorganization to wind reduction in the northern Mu Us Desert.

The development and transformation of barchan-parabolic dune can be led by vegetationestablishment, which may be induced by climate change (precipitation, temperature, andwind strength) and/or human intervention. The impact of wind strength change-inducedvegetation restoration on dunes morphology and theirs surface sedimentary features isneglected in the Maowusu Sandy Land. In this study, we combined datasets of NormalizedDifference Vegetation Index (NDVI) and climatic factors to analyze temporal changes invegetation growth and their response to changes in temperature, precipitation and windstrength in the northern margin of Maowusu Sandy Land from 1982 to 2015. Growing seasonNDVI is related to the significant decrease in drift potential (DP) during the entire studyperiod. Further temporal analyses indicate that the growing season NDVI trends are largelycontributed by wind strength and temperature changes during the earlier study period1982-2006. And then, the increasing NDVI is consistent with the slightly increasing trend ofprecipitation during the recent study period 2006-2015. Thus, the transformation ofthe transitional dune cannot be explained by the increasing trend of wind strengthchange-induced vegetation alone. During the recent period, once dunes are covered byvegetation, the change in wind strength cannot mobilize the stable dunes becausethe vegetation provides an effective buffer preventing sand erosion. To reveal theresponse of sedimentological reorganization during the dune transformation processes,grain-size characteristics along the longitudinal profile of three different types of duneswere examined. From barchan dune through transition dune to parabolic dune, withthe increase of the fine sands (125-250μm) proportions, the mean grain size MZgradually decreases; in addition, as the very fine sands (<125μm) class increases, thesorting σ1 of sand dunes gradually became worse. The decreasing wind strengthlead to partly transport of fine sands on the upper part of dune windward slope,resulting in the progress coarsening and the reduction of dune height at the crestarea. No distinct trend in sorting and mean grain size on the windward slope oftransition dune, indicating that sand in transport had little influence on the particle sizedistributions. Conversely, the progressive of sorting and coarsening of sands towards thecrest of parabolic dune, implying that vegetation limited the sands from upwind ofdune, changed the effective source of dune into the underlying source deposits orreworking pre-existing aeolian deposits and trapped the sands on the crest area. [ABSTRACT FROM AUTHOR]