Grain Size Characteristics Of The Surface Sand Of The Dunes In Cele Oasis-desert Zone

The Cele oasis-desert transition zone was the intermediate zone connecting the oasis and the desert.It was particularly affected by wind and sand throughout the year.Sand dunes was the main landform type in the transition zone.Through studying the grain size of sand dunes(Echo dunes,Nebkhas and Shadow dunes),It provides a theoretical basis for wind-proof and sand-fixed in the transition zone,reduction of wind-sand disasters in oasis areas,and improvement of the ecological environment stability in this area.The 308 sand materials on the surface of sand dunes were collected in this paper.Firstly,the surface grain size characteristics of Nebkhas under different coverage and different sizes of Echo dunes,Nebkhas and Shadow dunes were analyzed.Secondly,the variation of fractal dimension of different types of dunes and the relationship between fractal dimension and grain size were analyzed,discuss the influence of coverage and the size of obstacles on the grain size of sand dunes,and the characterization of the fractal dimension of sand material grain size.The following Conclusions:(1)As the coverage of the vegetation increases,the sand material grain size gradually become finer,the sorting becomes worse,the skewness becomes negative,and the kurtosis becomes narrower on the alhagi and tamarisk Nebkhas,the tamarisk Nebkhas grain size had the most obvious change(P<0.05).Under different coverage,the smallest grain size at the top of alhagi and tamarisk Nebkhas(68.248 and 62.010?m),and the largest grain size at the flanks(69.954 and 66.796?m),the skewness was Symmetrical and Fine,the sand material was Mesokurtic.(2)From the large,medium through small alhagi Echo dunes grain size gradually become finer,the sorting was getting worse.From the large,medium and small tamarix and karelinia Echo dunes grain size gradually become coarser,the sorting was getting worse and better.The vortex of Echo dune had the coarsest grain size and worst sorting,103.312?m and 1.786,the leeward slope of Echo dune had the finest grain size and better sorting,85.976?m and 1.424,the skewness was Symmetrical or Fine,the sand material was Mesokurtic.(3)The large,medium and small alhagi Nebkhas grain size became finer,the sorting was getting worse.From the large,medium and small Tamarix and Karelinia Nebkhas grain size gradually became coarser,the sorting was getting worse and better.The coarsest and finest grain size of Nebkhas appear on the windward slope and top of dune,respectively 77.365 and 72.282?m,the windward and leeward slope of Nebkhas were worst and better sorting,respectively 1.506 and 1.442,all the sand material were symmetrical Skewness and Mesokurtic kurtosis.(4)The large,medium and small alhagi and tamarisk Shadow dunes grain size gradually become finer,the sorting was getting better and worse.The large,medium and small karelinia Shadow dunes gradually become coarser,the sorting was getting better.The windward slope of Shadow dune had the coarsest grain size and worst sorting,86.035?m and 1.487,the leeward slope had the finest grain size and better sorting,82.308?m and 1.440,along the main wind direction,the sand grain size of dunes gradually become coarser,therefore,the extension of wind shadow dunes in the downward wind direction may cause the soil particles become to coarse and accelerate the speed of soil degradation.Different parts were Symmetrical skewness and Mesokurtic kurtosis.(5)From the fractal dimension of sand dune grain size,with the increase of shrub coverage,the fractal dimension of alhagi and tamarisk Nebkhas gradually increased.The fractal dimensions of large,medium and small alhagi and karelinia Echo sand dunes gradually decreased,and the fractal dimension of tamarisk Echo sand dunes gradually increased.The fractal dimension of large,medium and small alhagi and tamarisk Nebkhas gradually increased,while the fractal dimension of karelinia Nebkhas gradually decreased.The fractal dimensions of large,medium and small alhagi,tamarisk,and karelinia shadow dunes gradually increase.The fractal dimension of Echo dunes,Nebkhas and Shadow sand dunes had a very significant linear negative correlation with very fine sand,and had a significant linear positive correlation with sand particles,while the correlation with finer sand is not fixed.The above analysis shows that the greater vegetation coverage,the better wind-proof and sand-fixed effect of Nebkhas,therefore,in a degraded ecosystem,Nebkhas had a dual function.On the one hand,it is a sign of land degradation for the initial stage of environmental degradation.On the other hand,when there are more Nebkhas,it has the function of ecological protection.In addition,from the perspective of the types of shurbs,karelinia shurb is easier to intercept finer particles,while the alhagi and tamarisk shurb is easier to intercept coarse particles.From the size of dunes,The larger tamarisk and karelinia Nebkhas,the larger the Echo dunes and Nebkhas,it has stronger ability to intercept fine-grained materials near the surface,reducing the intrusion of fine dust in the atmosphere into the oasis.The larger shadow dune has the more coarse particles in the tail,it will easily evolute into linear dunes under suitable wind and landform conditions,which will harm the oasis ecology.Therefore,vegetation sand barriers should be setted reasonably in the transition zone,and the evolution process of shadow sand dunes should be paid attention to prevent sand dunes to invad the oasis.In addition,it is necessary to use groundwater resources rationally in oasis,divert water for irrigation to develop oasis agriculture,plan the area of oasis and agricultural reclamation reasonably,preventing soil erosion from aggravating.