【作者】 解云虎；

【导师】 汪季； 党晓宏；

【作者基本信息】 内蒙古农业大学 ， 水土保持与荒漠化防治， 2020， 博士

【摘要】 荒漠-绿洲过渡带是荒漠和绿洲两种自然景观转化最为剧烈、表现最突出的地区,是介于荒漠和绿洲之间的特殊生态脆弱带。腾格里沙漠东南缘常年受西风环流控制,干旱少雨,蒸发量大,光照充足,无霜期长,风大沙多,多年来不合理的人为活动,使该区土地沙化,草场退化,生态失调,自然环境十分恶劣,不仅严重制约着本地经济社会的发展,对东中部地区的生态安全和环境质量也构成严重威胁。针对腾格里沙漠东南缘荒漠-绿洲过渡带所面临严峻的土地沙化形势,亟需开展荒漠-绿洲过渡带沙化土地治理工作。本研究以腾格里沙漠东南缘格林滩为研究区,分析近30年格林滩土地沙化现状及演化趋势,确定风蚀发生敏感区位置,既荒漠-绿洲过渡带范围,分析土地沙化气候因素响应,并以此为依据,在格林滩荒漠-绿洲过渡带组建完善的绿洲防护体系,通过野外观测其风沙流特征、地表蚀积状况、沙尘沉降规律等评价防护体系防风阻沙效益,主要得出以下几点结论:(1)格林滩沙化土地类型划分为重度沙化土地、中度沙化土地、轻度沙化土地及未沙化土地,面积分别为15.23km2、23.98km2、26.69km2、13.64km2,分别占研究区总面积的23.11%、36.39%、40.50%和17.15%。轻度沙化土地主要分布于研究区西部、南部及农田区的北部及东部,中度沙化土地主要分布于农田外围与荒漠的过渡地区,重度沙化土地分布于研究区中部和南部。中度沙化土地为研究区沙化土地中转化最为频繁的土地利用类型,其分布区是潜在的土地沙化发生区,以此确定该区域为荒漠-绿洲过渡带。(2)荒漠-绿洲过渡带组建完整防护体系,防护体系组成西北～东南向由裸沙丘、沙障固沙带、灌草防风阻沙带和农田防护林网组成,其中农田防护林网主林带以两行一带为主,副林带主要以一行一带为主。灌草防风阻沙带位于农田防护林网和腾格里沙漠之间的过渡区,以天然灌木为主,覆盖度在10%～25%之间,带宽约500m。机械沙障固沙带位于灌草防风阻沙带外围裸沙丘,东北～西南向长度2.5km,宽290m,沙障材料为麦草,规格为1m×1m,防护体系划分为三个防护段面,分别为BF断面(包含裸沙丘和农田防护林网)、BSSF断面(包含裸沙丘、沙障固沙带、灌草防风阻沙带和农田防护林网)和BSF断面(包含裸沙丘、灌草防风阻沙带和农田防护林网)。(3)防护体系近地层0～30cm风速变化明显,随着高度的增加防风效能值降低,6.67m/s测风条件下,靠近地表植被影响显著层防风效能值最高可达87.46。不同防护带内随高度的变化风速廓线整体呈J型分布,且符合对数函数分布规律,研究区风沙输送主要发生在4月、5月和10月,农田防护林网的输沙量:BSSF断面<BSF断面<BF断面,防护体系对阻滞风沙输移效果显著,平均相对湿度与月总输沙量之间存在显著的负相关关系,月平均风速和沙尘暴日数的增加是月总输沙量增加的主要影响因素。(4)研究区蚀积状态主要以侵蚀为主,BSSF断面在不同月份由裸沙丘-沙障固沙带-灌草防风阻沙带侵蚀厚度逐渐降低,到农田防护林网略有堆积,不同风速梯度条件下,随着风速的加大,平均侵蚀厚度增加,BSSF断面农田防护林网主要以堆积为主,相比其他两个防护断面,堆积厚度相对增加,侵蚀厚度减少。蚀积强度的变化与蚀积量之间存在着明显的相关性,BSSF断面在阻滞风沙、降低侵蚀强度相对比其他两个防护段面效果更明显。(5)沙障固沙带表土平均粒径1.79Φ,相对比裸沙丘细化,灌草防风阻沙带和农田防护林网沉积物颗粒峰度值分别为1.0212和1.0020,均大于裸沙丘,土壤颗粒粒度分布相比裸沙丘分散。沉积物颗粒频率分布曲线均呈单峰型,沙障固沙带和灌草防风阻沙带颗粒分布相对比裸沙丘峰值降低且提前出现,颗粒分布范围变宽,研究区内细沙和中沙颗粒容易受到风沙活动的影响,极细沙和细沙为主要的风蚀颗粒,是影响防护体系内沉积物颗粒相对粗细的关键组分。(6)防护体系降尘主要发生在4月和5月,由裸沙丘-农田防护林方向降尘量逐渐减少,不同防护断面间相同防护带沙尘沉降速率BSSF断面>BSF断面>BF断面,BSSF断面裸沙丘和沙障固沙带沙尘沉降速率和风速之间存在着显著的线性相关关系。随着风速的增加,各防护带沙尘沉降速率逐渐增加,沙尘沉降颗粒物主要以局地物质为主,远源物质含量较低。更多还原

【Abstract】 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.更多还原