塔里木盆地西北部3种典型下垫面风沙活动特征

风沙流结构是风沙活动特征和土壤风蚀发生过程研究的核心内容。选取塔里木盆地西北部阿克苏地区棉田、枣园和沙漠-绿洲过渡带3种典型下垫面为研究对象,对比分析3次强风条件下不同耕作方式的农田地表和沙漠-绿洲过渡带的风沙流结构特征。结果表明:沙漠-绿洲过渡带由于近似于天然的流沙面,风沙流结构符合幂函数规律,在0~30 cm高度内的输沙量占到总输沙量的88.3%,这一结果高于在塔克拉玛干沙漠其他地区的观测水平;在农田下垫面条件下,由于受到土壤耕作方式和地表植被的影响,风沙流结构发生了很大变异,在0~2 m高度内不再符合幂函数变化规律;沙漠-绿洲过渡带表现出比农田下垫面更大的风沙流的强度,强度从4.08 g·m-1到187.69 g·m-1;覆膜棉花的种植在一定程度上抑制了农田的土壤风蚀。     

旱地保护性耕作土壤风蚀模型研究

在分析国外风蚀模型资料的基础上,建立了适用于保护性耕作的风蚀模型。该模型以小时为步长,根据气象数据、地表土壤水分、秸秆残茬覆盖率及地表粗糙度,模拟不同耕作体系下农田土壤风蚀流失量情况;针对保护性耕作的特点,考虑到残茬覆盖对土壤含水量和地表粗糙度的影响;通过田间风蚀测定数据的验证,证明所建立的保护性耕作风蚀模型的模拟值与实测值比较吻合。     

呼伦贝尔沙质草原风蚀坑地表风沙流结构特征

在呼伦贝尔沙质草原北部沙带中段风蚀坑集中分布区内,选取不同发育阶段的风蚀坑,通过同步观测风蚀坑地表(0～200 cm)风速及输沙通量,分析并比较风沙流结构特征,为呼伦贝尔沙质草原风蚀坑治理提供理论依据。研究表明:在裸地沙斑、活跃发展、固定阶段及重新活化阶段的风蚀坑,风速廓线基本遵循对数分布规律;而在未风蚀草地、消亡阶段的风蚀坑,气流受下垫面扰动,呈"S"形分布。风蚀坑各发育阶段输沙量与高度的最优拟合模型为负指数模型,不同发育阶段风蚀坑内部风沙流输沙量差异较为明显;超过95%的输沙量均在地表0～30 cm高度内,且63. 97%～90. 96%的输沙量集中分布在距地表10 cm高度内。风沙流跃移高度与风速正相关,依次为:活跃发展重新活化裸地沙斑固定阶段消亡阶段未风蚀草地。通过分析风沙流通量系数,可知在裸地沙斑、活跃发展及重新活化阶段,输沙量有向高层移动的趋势;而在其他阶段,由于植被盖度较高,使得风沙流多集中在近地层。     

残茬高度对土壤风蚀量影响的试验研究

在内蒙古自治区武川县建立农田土壤风蚀试验区,采用内蒙古农业大学研制的移动式风蚀风洞和旋风分离式集沙仪,观测不同残茬高度条件下农田土壤的风蚀情况.试验结果表明:土壤风蚀量和扬起沙尘的高度随风速的增加而增加,随着作物秸秆残茬高度的增加而降低,且风蚀量与高度变化符合指数函数关系,土壤颗粒主要集中在近地表层内运动.保护性耕作可明显地提高起沙风速,减少农田土壤损失,当秸秆高度为30 cm时,风蚀量仅为传统耕地的1/4左右.     

沙漠公路防护林不同林带位置的风沙流结构

利用BSNE集沙仪对沙漠公路两侧防护林的近地表风沙流结构进行研究,结果表明:(1)随着高度的增加,不同林带位置上部的输沙量趋于一致,各点风沙流输沙量差异主要集中在近地表处,而植被覆盖与否对近地表气流中的输沙量有决定性作用,输沙量表现为:迎风面流沙地林带间背风面林带内。(2)迎风面及流沙地风沙流输沙量主要分布在距地表20 cm高度内,背风面则集中分布在50 cm高度内,均占观测高度输沙总量的74%以上,林带间及林带内风沙流输沙量在各高度层分布较为平均,介于11%~23%之间。(3)护林体系外(迎风面、背风面及流沙地),风沙流输沙垂直分布差异很大,输沙量随高度增加呈幂函数形式降低,而防护林体系内(林带间及林带内),风沙流垂直分布差异趋于减小,输沙量随高度增加呈多项式形式先降低后增加。     

河北坝上风蚀对农田土壤肥力水平影响研究

河北坝上地区风多风大,冬春季节降水少,使得大片农田长期处于强烈的风蚀之中.由于地表土壤养分的大量流失,农田土壤生产能力下降,导致荒漠化进程加剧.针对传统和保护性耕作农田土壤及风蚀物养分的变化,研究分析了土壤的风蚀和有机物及养分衰减的定量关系及其衰减的机理.结果表明:风蚀过程是农田土壤退化的重要路径,可以通过风蚀物中有机质和养分的含量估算农田土壤的有机质和养分的损失量.土壤风蚀过程中,保护性耕作比传统耕作可以减少风蚀量62.56%.有机质损失减少31.05%,全氮损失减少29.15%,全磷损失减少32.25%,全钾损失减少66.11%;有机质及养分主要集中在细微的土壤颗粒之中.风蚀对土壤营养物质及有机质的流失高于土壤的流失,风蚀是土壤退化的重要原因,恶化环境的同时造成了严重的经济损失.可以采用保护性耕作技术防止农田沙漠化和提高作物产量.     

保护性耕作技术对农田环境的影响研究

根据保护性耕作在我国的实施情况并结合国外已有研究结果,我们认为保护性耕作的内涵为：保护性耕作措施就是对农田实行少耕或免耕,尽可能减少对土壤的扰动,并以秸秆覆盖地表,达到减少劳动强度和生产投入,防止农田风蚀和水蚀并提高土壤肥力和抗旱能力的一种农田耕作技术。并对保护性耕作措施在改善农田作物生长环境方面的作用：有效提高农田水分利用效率;有效保持水土,大幅度地减少水土流失,减少大部分的田间起沙,降低农田地表土壤养分和水分的流失;有效提高土壤生物和微生物的数量与活性,增加土壤肥力,改善土壤结构,降低地表温度,减少地表蒸发等方面的最新研究成果进行了综述。此外,还叙述了保护性耕作对农田病虫害和杂草的影响。最后提出了在我国开展保护性耕作的必要性及其工作重点。     

土壤风蚀量随残茬高度的变化规律研究

在内蒙古自治区武川县建立农田土壤风蚀试验区,采用内蒙古农业大学研制的移动式风蚀风洞和旋风分离式集沙仪,直接在农田上观测不同残茬高度条件下的农田风蚀土壤损失情况。试验结果表明:土壤风蚀量和扬起沙尘的高度随风速的增加而增加,随着作物秸秆残茬高度的增加而降低,且输沙量与高度变化符合指数函数关系,土壤颗粒主要集中在近地表层内运动。保护性耕作可明显地提高启沙风速,减少农田土壤损失,当秸秆高度为30 cm时,风蚀量仅为传统耕地的1/4左右。     

沙河洼农田地表风沙运动与土壤风蚀的初步研究

本文通过对农田不同地表类型的粗糙度，对近地层气流运动状态、风沙流结构特征、输沙量进行了研究，指出改变农田地表性质，就可在一定程度上防止土壤风蚀的发生。     

小麦留茬对陕北农田风蚀影响的室内风洞模拟

作为风蚀区主要保护性耕作措施之一,秸秆留茬覆盖可以通过增加地表粗糙度(Z0)减少近地表风速和侵蚀动力,并缩短风蚀颗粒的搬运距离和搬运高度,从而减少地表风蚀量.本研究采用室内模拟风洞实验,测定并分析了陕北2种主要土壤类型(风沙土和黄绵土)在4个风速、3种小麦留茬高度和2种留茬行距处理下土壤风蚀强度和在0～60 cm风洞断...     

植被沙障对近地表风沙流特征影响的风洞实验

植被沙障在一些地区已成为沙害防治的有效手段,其应用也越来越广泛,但对其治沙机理尚不很清楚.在盖度为10%,15%,20%,30%,40%,60%情况下,对植被沙障的防风固沙效益进行了风洞试验.实验风速设置为6,8,11 m/s,测定不同植被盖度的风速廓线特征、风沙流结构特征及其防沙效果.实验结果表明:①积沙总量随盖度增加而逐渐降低,风沙流中的砂粒分布在一定的高度范围内,但分布的高度随盖度的增加呈下降趋势;②植株的茂密程度对风沙流的结构有明显影响,盖度越高,积沙量越集中在下部;③盖度并不是导致积沙量为零的唯一指标,风蚀是否发生,还与植被的疏透度、防护林的高度等有关.     

Wind tunnel test on the effect of metal net fences on sand flux in a Gobi Desert,China

The Lanzhou-Xinjiang High-speed Railway runs through an expansive windy area in a Gobi Desert, and sand-blocking fences were built to protect the railway from destruction by wind-blown sand. However, the shielding effect of the sand-blocking fence is below the expectation. In this study, effects of metal net fences with porosities of 0.5 and 0.7 were tested in a wind tunnel to determine the effectiveness of the employed two kinds of fences in reducing wind velocity and restraining wind-blown sand. Specifically, the horizontal wind velocities and sediment flux densities above the gravel surface were measured under different free-stream wind velocities for the following conditions: no fence at all, single fence with a porosity of 0.5, single fence with a porosity of 0.7, double fences with a porosity of 0.5, and double fences with a porosity of 0.7. Experimental results showed that the horizontal wind velocity was more significantly decreased by the fence with a porosity of 0.5, especially for the double fences. The horizontal wind velocity decreased approximately 65% at a distance of 3.25 m(i.e., 13 H, where H denotes the fence height) downwind the double fences, and no reverse flow or vortex was observed on the leeward side. The sediment flux density decreased exponentially with height above the gravel surface downwind in all tested fences. The reduction percentage of total sediment flux density was higher for the fence with a porosity of 0.5 than for the fence with a porosity of 0.7, especially for the double fences. Furthermore, the decreasing percentage of total sediment flux density decreased with increasing free-stream wind velocity. The results suggest that compared with metal net fence with a porosity of 0.7, the metal net fence with a porosity of 0.5 is more effective for controlling wind-blown sand in the expansive windy area where the Lanzhou-Xinjiang High-speed Railway runs through.     

沙漠地区风沙活动特征——以中国科学院风沙观测场为例

运用中国科学院风沙科学观测场的实测资料,对腾格里沙漠风沙环境特征进行初步分析,内容包括起沙风、风沙活动强度、风沙流结构和沙漠边界层的风速廓线.该地区的起沙风以6～8 m/s为主,占总起沙风的71.63%,其次为8～10 m/s,占19.24%,两者之和占90.87%;大风日数为4天;风向以W-N组风向为主;占全年的53.14%.年输沙势为36.56VU,风能属于低风能环境,单一主风向和单风态风环境.风沙流主要集中在地表的0.1 m,占总输沙量的95.46%.观测场近地层厚度大于50 m.     

Effect of the W-beam central guardrails on wind-blown sand deposition on desert expressways in sandy regions

Many desert expressways are affected by the deposition of the wind-blown sand,which might block the movement of vehicles or cause accidents.W-beam central guardrails,which are used to improve the safety of desert expressways,are thought to influence the deposition of the wind-blown sand,but this has yet not to be studied adequately.To address this issue,we conducted a wind tunnel test to simulate and explore how the W-beam central guardrails affect the airflow,the wind-blown sand flux and the deposition of the wind-blown sand on desert expressways in sandy regions.The subgrade model is 3.5 cm high and 80.0 cm wide,with a bank slope ratio of 1:3.The W-beam central guardrails model is 3.7 cm high,which included a 1.4-cm-high W-beam and a 2.3-cm-high stand column.The wind velocity was measured by using pitot-static tubes placed at nine different heights(1,2,3,5,7,10,15,30 and 50 cm)above the floor of the chamber.The vertical distribution of the wind-blown sand flux in the wind tunnel was measured by using the sand sampler,which was sectioned into 20 intervals.In addition,we measured the wind-blown sand flux in the field at K50 of the Bachu-Shache desert expressway in the Taklimakan Desert on 11 May 2016,by using a customized 78-cm-high gradient sand sampler for the sand flux structure test.Obstruction by the subgrade leads to the formation of two weak wind zones located at the foot of the windward slope and at the leeward slope of the subgrade,and the wind velocity on the leeward side weakens significantly.The W-beam central guardrails decrease the leeward wind velocity,whereas the velocity increases through the bottom gaps and over the top of the W-beam central guardrails.The vertical distribution of the wind-blown sand flux measured by wind tunnel follows neither a power-law nor an exponential function when affected by either the subgrade or the W-beam central guardrails.At 0.0H and 0.5H(where H=3.5 cm,which is the height of the subgrade),the sand transport is less at the 3 cm height from the subgrade surface than at the 1 and 5 cm heights as a result of obstruction by the W-beam central guardrails,and the maximum sand transportation occurs at the 5 cm height affected by the subgrade surface.The average saltation height in the presence of the W-beam central guardrails is greater than the subgrade height.The field test shows that the sand deposits on the overtaking lane leeward of the W-beam central guardrails and that the thickness of the deposited sand is determined by the difference in the sand mass transported between the inlet and outlet points,which is consistent with the position of the minimum wind velocity in the wind tunnel test.The results of this study could help us to understand the hazards of the wind-blown sand onto subgrade with the W-beam central guardrails.     

Sand flux estimation during a sand-dust storm at Tazhong area of Taklimakan Desert, China

In this paper, the sand transport during a sand-dust storm in the Tazhong area of the central Taklimakan Desert from 11:29 to 23:56 on July 19, 2008 was observed and measured in real time. The sand flux at Tazhong was estimated using sand transport empirical formulas. The critical friction velocity at Tazhong was 0.24 m/s and the functional relation between the wind speed and sediment discharge at the height of 2 m was established. It was also found that the calculated values by Lettau's sediment discharge formula were close to those of the instrument measurements. The horizontal sand flux and the vertical sand flux during this sand-dust storm at Tazhong were respectively 258.67×10-4 kg/(m·s) and 40.07×10-7 kg/(m2·s).     

灌木林优化配置格局对土壤风蚀的影响

低覆盖度时,灌木林的水平配置格局成为制约土壤风蚀的重要因素。以宁夏盐池县风沙区人工灌木林基地为试验区,研究了不同下垫面类型和不同配置格局的灌木沙障对风速、近地表输沙率和地表粗糙度的影响。结果表明:灌木林的防治土壤风蚀能力与灌木林的种类、高度和配置格局有直接关系:行带式配置能显著提高灌木林的防风效果,其中以沙柳林效果最佳;三行一带、平均高1.5m、行距1.5m、插深0.5m配置规格的沙柳沙障对地表土壤风蚀的控制效果最好,但防护范围限15倍带高以内;在行数一定的情况下,沙障高度越低,控制土壤风蚀能力越强。     

策勒绿洲-荒漠过渡带风沙前沿近地表沙尘水平通量观测

沙漠地区近地表水平输送的沙尘物质通量及其随高度的变化是沙尘输送过程的重要表现特征。在塔克拉玛干沙漠南缘策勒绿洲-荒漠过渡带风沙前沿平坦沙地的风沙观测场,利用BSNE集沙仪对近地表（2 m）不同高度沙尘物质的水平输送进行了观测,对其随高度变化特征进行了分析,并对近地表水平运动的沙尘通量进行了计算。结果表明：观测点沙尘物质的水平通量随高度的增加而减小,与高度的关系可用幂函数和指数函数表示;55%～58%的沙尘量在地表0.5 m高度以内传输;73%～75%在地表1 m高度以内传输;87%～89%在地表1.5 m高度以内传输;2010年5月25日至2011年5月24日,通过0～2 m高度的单宽总输沙量为1 846.7 kg•m^-1;其中PM80、PM50的输送量分别为1 192.0 kg•m^-1、387.9 kg•m^-1。