Gurbantunggut Desert Dune Landform And Its Development Environment

In this thesis,the high-resolution remote sensing images and meteorological data used are from Gaofen-1 satellite,Google Earth,Bigemap,and Modis.Field observation and sampling,indoor testing including sediment particle size classification,chemical elements,mineral composition,microstructure SEM,magnetic susceptibility,soil organic carbon,organic matter and other nutrient testing are used to study the aeolian geomorphology and its development environment in Gurbantunggut Desert.This thesis focuses on four issues:First,what types of aeolian geomorphology are there in the Gurbantunggut Desert?What are their aeolian geomorphology characteristics and their distribution patterns?Second,what is the environment of the wind regime in the study area?What are the temporal and spatial changes at this environment?What is the relationship between wind regime and various dunes landforms?Third,what are the similarities and differences of sediments in various types of desert landscapes and how to impact on the dune landforms?Fourth,what is the composition of the flora in the study area?And what are the temporal and spatial changes of vegetation coverage and soil nutrients in different sites and depths of different dune types?And how ecoenvironment impact on the dune landforms?After an in-depth analysis of the above issues,the conclusions are as follows:1.According to the change process of the fixed,semi fixed and liquidity took place alternativly in Quaternary Period,the wind energy,the shape and scale,which have occurred continuously in the study area,the dune landform of Gurbantunggut Desert is divided into three categories:horizontal,vertical and symmetrical sand dunes,29 species in total.The spatial distribution map of different dune types with a total area of 41,000 square kilometers was drawn.Among them,fixed and semi-fixed dunes occupy 83.35%,and mobile dunes are 16.65%.2.The morphological parameters such as the length of the windward slope,the length of the leeward slope,the width of the ridge,the length of the sand ridge,the average ridge line direction,the width of the gap,the number of intersection nodes,the angle between the main and auxiliary beams,the area size and the height were measured.The length of each type of dune is divided into two orders of magnitude,bounded by 1km;the height is divided into three orders of magnitude,which are 10m,10-3 0m,and more than 30m;the spacing can also be divided into three orders of magnitude:100m,3 00m,and 1km.Except for symmetrical dunes,both horizontal and vertical dunes have development trends related to wind energy.Unlike other studies of desert dunes,the height,ridgeline length,and spacing of the dunes in the Gurbantunggut Desert do not correspond well.3.The Gurbantunggut Desert is controlled by the westerly circulation throughout the year,and it will also be affected by the Mongolia-Siberian high in winter.There was little change in air pressure throughout the year.The surface wind field mainly has four characteristics of branching,turning,convergence and divergence,which vary significantly from month to month.Except for winter,there are two branches,mostly around 86.5 °E and 88 °E.Convergence and divergence occur mainly in the marginal areas of the desert.From 1960 to 2018,the average wind speed in the study area was 2.0m·s-1,and the average maximum wind speed was 4.9m·s-1,both of which began to increase sharply in spring.The wind regime environment is negatively correlated with both temperature and precipitation.The main direction of wind and sand is west,the secondary direction is north.In terms of time,spring and summer are higher,while winter is the lowest.Spatially,it is the largest in the north and the smallest in the East.Since 1960,the annual total sand transport potential in the study area has fluctuated twice,showing an overall downward trend.The average annual sand transport potential is 106UV,which is a low wind regime environment.The Wind Rose Diagram generally has a wide single-peak wind condition,and the RDP in all four seasons is east-southeast.In terms of time,it is the largest in summer and the smallest in winter.Spatially,it is highest in the west and lowest in the east.The horizontal dunes are dominated by the narrow single wind state of northwest by west.The longitudinal dunes are dominated by the northwest and north sharp bimodal wind state.The symmetrical dunes are dominated by the complex wind conditions of northwest by west,southwest and north.The wind regime environment corresponds well with the distribution and morphology of various dune landforms.The size and direction of sand transport potential energy affect the shape and scale of sand dunes.The change of sand transport direction also impacts on the trend of dune ridge line.4.The color of the sediments in the Gurbantunggut Desert is yellow,red,and mixed colors which formation related to the landform location.The desert is mainly composed of fine sand and medium sand.The grain size of the desert gradually narrows from northwest to southeast.The natural frequency distribution curve of sediment particle size is dominated by bimodal.The average particle size is 2.08? and the sorting,skewness and kurtosis range are large.Except for the barchan dunes(chains),parabolic dunes and compound honeycomb dunes that are dominated by aeolian sedimentary environments,the rest are dominated by shallow seas.It is a good responde between the scale distribution of various sand dunes and the grain size characteristics of sediments.5.The quartz particles in the sediment are mainly round,and the roundness is mostly angular.From the perspective of mechanical action:dished pits under the action of aeolian forces have a greater probability of appearing in the sand dunes with smaller distances.The occurrence of rubbing marks under the action of glaciers in the north of the central desert is greater than that in the south and east,and it is related to the distance of transportation.The size of the overall pit is directly related to the granularity characteristics.From the perspective of chemical action:the northern dunes are related to the silicon substances accompanying the stripping from the western mountains,while the southern dunes are affected by complex wind conditions and silicon-soluble substances accumulate.In all types of sand dune sediments,the content of SiO2 and Ba is the highest.The differences of common and trace elements in various dunes are small.In different parts of the dune,the content of the top of the slope is usually the lowest,and the windward and leeward slopes are significantly different.Compared with the average content of UCC,the trace element Co showed extremely significant enrichment,and the enrichment of barchan dunes(chains),parabolic dunes and dendritic longitudinal ridges is higher.The losses of Cu,Nb and Th are serious,and the leaching degree of grid-like dunes,ridge-honeycomb dunes(H)and compound honeycomb dunes are greater.The leaching coefficient and the residual coefficient are well fitted.The sand material is deposited in a cold and dry environment and lacks an effective chemical weathering process.6.There are 158 species of plants,31 families,and 118 genera in the whole study area,including 36 species of trees and shrubs and 122 species of herbs.The short-lived plants are the dominant desert life forms.Since 2000,the vegetation coverage rate was mostly less than 20%,and the main body of the desert showed a negative change,and the vegetation in the east and west extension zone recovered and improved.The water content increases with depth,and the wet sand layer at the foot of the slope is higher than the top of the slope.The organic carbon content is slightly higher in the west,east and north of the main desert,and lower in most areas of the south of the center.The organic matter content is highest in the southwest of the main body of the desert,and very low on the west and east sides.The distribution of the content of alkali-hydrolyzed nitrogen showed obvious characteristics of more middle part and less two sides.The overall topsoil of the desert is alkaline and the total salt content is not high.The heterogeneity of soil nutrient content in different dune types and different dune locations is stronger,and the southern part is more conducive to vegetation growth than the northern part.In general,soil water and nutrients determine the species and growth of vegetation,and the composition and coverage of vegetation flora affect the size of sand dunes,and the growth period affects the sand surface mobility.