| Desert-oasis ecotone is a special ecological fragile zone between desert and oasis,where the transformation of two kinds of natural landscapes is the most intense and prominent.The southeast edge of the Tengger Desert is controlled by the westerly circulation all the year round.It is located on the edge of the East Asian monsoon.It is drought and little rain,high evaporation,has sufficient sunlight,has a long frost-free period,is windy and Sandy,and has been subjected to unreasonable human activities for many years,resulting in desertification of the land and degradation of the grassland in the area,the ecological imbalance and the bad natural environment not only restrict the development of local economy and society,but also threaten the ecological security and environmental quality of the East and central region.In view of the severe situation of desertification in the desert-oasis ecotone on the southeastern edge of the Tengger Desert,it is urgent to carry out desertification control work in the desert-oasis ecotone.In this study,the present situation and evolution trend of land desertification in Green Beach in the southeast edge of Tengger Desert were analyzed,and the location of sensitive area for wind erosion was determined,based on the analysis of the response of climatic factors to land desertification,a perfect protective system of oasis was constructed in the Gelintan desert-oasis ecotone,through field observation of the characteristics of wind-blown sand flow,surface erosion and deposition,and the law of sand-dust deposition,the benefit of wind and sand prevention of the protection system is evaluated,the main conclusions are as follows:(1)The types of sandy land in Green Beach are divided into heavy sandy land,moderate sandy land,light sandy land and unsandy land,the area is 15.23 km2,23.98 km2,26.69 km2,13.64 km2,respectively,they accounted for 23.11%,36.39%,40.50%and 17.15%of the total area respectively.The lightly desertified land is mainly distributed in the west,south and the north and east of the farmland area,the moderately desertified land is mainly distributed in the transitional area between the periphery of farmland and the desert,and the heavily desertified land is distributed in the central and south of the research area,the moderate desertification land is the most frequently transformed land use type in the study area,and its distribution area is the potential land desertification area,so this area is defined as the desert-oasis transition zone.(2)A complete protective system has been established in the desert-oasis ecotone,comprising bare sand dunes,sand-barrier belts,shrub-grass windbreak sand-blocking belts and farmland shelterbelt nets in the northwest-southeast direction,the main forest belt of farmland shelterbelt net is two rows,three rows and four rows are distributed in the southeast of farmland,and the secondary forest belt is one row.The shrub-grass windbreak zone is located in the transitional zone between the farmland shelterbelt and the Tengger Desert.It is mainly composed of natural shrubs,with a coverage of 10-25%and a bandwidth of about 500m.The sand-fixing belt of mechanical sand-barrier is located in the bare sand dune around the wind-resistant sand-barrier and shrub-grass.The length of sand-barrier is 2.5km and the width is 290m in the northeast-southwest Direction.The sand-barrier type is wheat grass,the size is 1m×1m,the length is about 2.5km and the width is 290m.The protection system is divided into three sections,BF section(including bare sand Dune and farmland shelterbelt),BSSF section(including bare sand Dune,sand barrier belt,shrub-grass belt and farmland shelterbelt)and BSF section(including bare sand Dune,shrub-grass belt and farmland shelterbelt).(3)The wind speed of 0-30cm in the surface layer of the protection system changes obviously.With the increase of the height,the wind-proof efficiency value decreases.The wind speed profiles in the different shelterbelts with different heights are J-shaped,and accord with the law of logarithmic function distribution.The sand transport in the study area mainly occurs in April,May and October,The amount of sediment transported is arranged as BSSF Section>BSF Section>BF section,the protection system has a significant effect on arresting wind and sand transport,and there is a significant negative correlation between average relative humidity and monthly total sediment transport,the increase of monthly average wind speed and the number of dust storm days are the main influencing factors for the increase of monthly total sediment.(4)The erosion and deposition state in the study area is mainly erosion,and the erosion thickness of the BSSF section decreases gradually in different months from bare sand dune,sand barrier sand,sand-fixing belt,shrub-grass windbreak sand-resisting belt to farmland shelterbelt,and there is a slight accumulation under different wind speed gradient,with the increase of wind speed,the average erosion thickness increases,and the accumulation of farmland shelterbelt net in BSSF section is dominant,compared with the other two sections,the accumulation thickness increases and erosion thickness decreases.There is obvious correlation between the change of erosion deposition intensity and the amount of erosion deposition.The effect of BSSF section is more obvious than the other two sections in blocking sand and reducing erosion intensity.(5)The sand-barrier belt is finer than bare sand Dune,the sand peak value of the sand-barrier and the farmland shelterbelt is bigger than bare sand Dune,and the soil particle size distribution is more dispersed than bare sand Dune.The sediment particle frequency distribution curves are unimodal,the sand-barrier belt and the shrub-grass belt have lower peak value and appear earlier than the bare sand dune,and the particle distribution range is wider,fine and medium sand particles are easily affected by wind-blown sand activities in the study area,and extremely fine sand and fine sand are the main wind erosion particles,which are the key components affecting the relative thickness of sediment particles in the protection system.(6)The dustfall of the protection system occurred mainly in April and May,the dustfall amount from bare sand dune to farmland shelterbelt decreased gradually,and the dust deposition rate of the same protection belt was higher in the BSSF section>in the BSF section>in the section BF,there is a significant linear correlation between sand-dust deposition rate and wind speed in bare sand dune and sand-barrier zone of BSSF section.With the increase of wind speed,the settling velocity of sand-dust in each protection zone increases gradually.The settling particulate matter is mainly local matter,and the remote matter content is low. |
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