Spectral properties, iron oxide content and provenance of Namib dune sands

This paper applies multispectral remote sensing techniques to map the Fe-oxide content over the entire Namib sand sea. Spectrometric analysis is applied to field samples to identify the reflectance properties of the dune sands which enable remotely sensed Fe-oxide mapping. The results indicate that the pattern of dune colour in the Namib sand sea arises from the mixing of at least two distinct sources of sand; a red component of high Fe-oxide content (present as a coating on the sand grains) which derives from the inland regions, particularly from major embayments into the Southern African escarpment; and a yellow coastal component of low Fe-oxide content which is brought into the area by northward-moving aeolian transport processes. These major provenances are separated by a mixing zone between 20 km and 90 km from the coast throughout the entire length of the sand sea. Previous workers have also recognised a third, fluvial, provenance, but the methodology applied here is not able to map this source as a distinct spectral component.     

腾格里沙漠沙丘沉积物粒度特征及其空间差异

沉积物粒度特征对于研究物源、衡量搬运能量具有重要意义。分析了腾格里沙漠45个沙丘顶部样品的粒度特征,并计算了30 a输沙势。结果表明：（1）沙丘沙以细沙（71%）和中沙（20%）为主,平均粒径2.38 Φ,分选系数0.40 Φ;平均粒径与分选系数、偏度呈良好的线性关系。（2）分选为“极好”和“好”的样品整体分布在沙漠中部和西南部,前者概率累计曲线趋于近对称、中等峰态,为二段式,后者趋于正偏、中等或尖窄峰态,为三段式;而沙漠边缘分选较差,概率累计曲线为多段式。（3）盛行起沙风为西北风。西北和东北部属中风能环境,风况属单峰型和复杂型;南部和东南部分别属低、中风能环境,均双峰型风况。研究区沙丘沙源应以下伏河湖相沉积物就地起沙为主。沙漠边缘河湖相沉积物应该为中部区沙丘沙提供了物源,西南部沙丘沙可能源自石羊河下游的冲洪积物,风力分选作用较长,边缘沙丘沙则应来源于该区河湖相沉积物就地起沙,风力分选不充分。粒度参数空间分布特征与沙丘类型和规模之间存在一定的耦合关系。     

萨拉乌苏河流域萨拉乌苏组砂丘砂沉积特征

The Salawusu Formation of Milanggouwan section in Salawusu River Valley includes 7 layers of paleo-mobile dune sands, and 4 layers of paleo-fixed and semi-fixed dune sands. Their structures have been observed and their grain size, surface textural features and several main chemical elements have been analyzed. The results showed that： 1） Some of the aeolian structural characteristics of these dune sands are similar to that of the recent dune sands. 2） They are also similar to the recent dune sands in grain size components, and parameters of Mz,σ, Sk and Kg, as well as in several main chemical components. 3） The scattergrams of Mz-σ and SiO2-Al2O3＋TOFE and the probability curves of grain size showed that these paleo-dune sands are different from paleosols and fluvio-lacustrine facies, but are consistency with recent dune sands. 4） Quartz sands have well roundness and surface textural features such as dish-shaped pits, crescent-shaped pits, pockmarked pits, upturned cleavage plates, siliceous precipitates and siliceous crevasses, indicating that they had been carried for a long time by the wind. As the 11 layers of paleo-dune sands possess the aeolian characteristics in structure, grain size, surface textural features and chemical elements, the origin of their formation should be attributed to eolation.     

Sedimentary characteristics of paleo-aeolian dune sands of Salawusu Formation in the Salawusu River Valley

The Salawusu Formation of Milanggouwan section in Salawusu River Valley in-cludes 7 layers of paleo-mobile dune sands, and 4 layers of paleo-fixed and semi-fixed dune sands. Their structures have been observed and their grain size, surface textural features and several main chemical elements have been analyzed. The results showed that: 1) Some of the aeolian structural characteristics of these dune sands are similar to that of the recent dune sands. 2) They are also similar to the recent dune sands in grain size components, and parameters of Mz, σ, Sk and Kg, as well as in several main chemical components. 3) The scattergrams of Mz-σ and SiO2–Al2O3+TOFE and the probability curves of grain size showed that these paleo-dune sands are different from paleosols and fluvio-lacustrine facies, but are consistency with recent dune sands. 4) Quartz sands have well roundness and surface textural features such as dish-shaped pits, crescent-shaped pits, pockmarked pits, upturned cleavage plates, siliceous precipitates and siliceous crevasses, indicating that they had been carried for a long time by the wind. As the 11 layers of paleo-dune sands possess the aeolian characteristics in structure, grain size, surface textural features and chemical elements, the origin of their formation should be attributed to eolation.     

Vegetation of dune sands of Olkhon Island on Baikal and some questions concerning its protection

The need for the conservation of vegetation on dune sands of Olkhon Island is substantiated. Psammophytic phytocenoses evolving on the sands are of rare occurrence, in their composition, structure and spread, for the Prebaikalia. Endemic and relict plant species constitute a rarity core of the flora of these cenoses. The state protection method for several tracts of sand landscape is suggested for biodiversity sustenance on the island.     

Fire-induced transformation of bog soils in the Ust’-Selenginskaya depression

A case study of the drained soils of the Posol’skii bog massif in the Republic of Buryatia showed a fire-induced degradation of peat soils resulting in pyrogenic formations which are distinguished for a peculiar kind of morphological and chemical properties.     

Dynamics of nebkhas superimposed on a parabolic dune and their effect on the dune dynamics

We report here on a bare barchan dune in Israel that converted over the last 60 years to a shrub-covered parabolic dune due to changes in land use. Thirty nebkhas (sand mounds) that were formed by sand trapped around shrubs growing on the dune were monitored during winter of 2004–2005. The rates of erosion or deposition were measured at five points in the nebkhas by erosion pins. All nebkhas were shown to undergo erosion or deposition activity. Nebkhas on the windward slope of the dune experienced primarily erosion. Those on the lee slope grew slowly by the light accumulation of sand. The largest nebkhas were found on the dune crest; they built up through the accumulation of sand that was eroded from the windward slope. There were no significant differences between the rates of erosion/deposition of the five study points placed in each nebkha. However, there were significant differences between the rates of erosion/deposition of the nebkhas on the three dynamic segments of the dunes (windward, crest and lee). A change in dune dynamics was observed by the emergence of shrubs on the crest. These shrubs trapped sand and increased the crest height. The sand trapped on the crest was not deposited on the lee side. In that case, the dune becomes narrower, higher, with a concave shape (of the windward slope), during the transformation from a barchan to a parabolic dune.     

新月形沙丘与线形沙丘共生现象探讨——以撒哈拉沙漠为例

沙丘共生问题是风沙地貌研究的热点,目前尚缺乏较为深入的探讨。以共生沙丘分布最为广泛的撒哈拉沙漠为例,基于Google Earth高清卫星影像对新月形沙丘和简单线形沙丘共生区域进行参数识别,并对其区域风况特征和形成发育环境进行分析,以探讨共生沙丘形成的可能原因。结果表明：撒哈拉沙漠共有17处典型的共生沙丘区域,是世界上最大的共生沙丘分布区。区域及单个共生沙丘形态参数之间均存在一定相关性,但并不具有理论上应具有的良好相关性,表明影响沙丘共生的因素较为复杂。共生沙丘在低、中、高风能环境以及不同风向变率下均可发育,但主要在低风能环境、中等风向变率,锐双峰风况下形成。单一的起沙风风向是共生沙丘形成的重要条件,合成输沙势方向与沙丘走向基本一致。除风况外,障碍物如山脉、河流等因素同样对沙丘共生发挥了重要作用。     

Transverse dune trailing ridges and vegetation succession

We describe the evolution of, and vegetation succession on, a previously undescribed landform: transverse dune trailing ridges at El Farallón transgressive dunefield in the state of Veracruz, Mexico. Three-dimensional clinometer/compass and tape topographic surveys were conducted in conjunction with 1 m² contiguous percent cover and presence/absence vegetation survey transects at eight locations across two adjacent trailing ridges. At the study site, and elsewhere, the transverse dune trailing ridges are formed by vegetation colonization of the lateral margins of active transverse, barchanoidal transverse, and aklé or network dunes. For simplicity, all trailing ridges formed from these dune types are referred to as transverse dune trailing ridges. Because there are several transverse dunes in the dunefield, multiple trailing ridges can be formed at one time. Two adjacent trailing ridges were examined. The shortest length ridge was 70 m long, and evolving from a 2.5 m-high transverse dune, while the longer ridge was 140 m long, and evolving from an 8 m-high dune. Trailing ridge length is a proxy measure of ridge age, since the longer the ridge, the greater the length of time since initial formation. With increasing age or distance upwind, species diversity increased, as well as species horizontal extent and percent cover. In turn, the degree of bare sand decreased. Overall, the data indicate a successional trend in the vegetation presence and cover with increasing age upwind. Those species most tolerant to burial (Croton and Palafoxia) begin the process of trailing ridge formation. Ipomoea and Canavalia are less tolerant to burial and also are typically the next colonizing species. Trachypogon does not tolerate sand burial or deposition very well and only appears after significant stabilization has taken place. The ridges display a moderately defined successional sequence in plant colonization and percentage cover with time (and upwind distance). They are significant geomorphologically as a unique landform in transgressive dunefields, and also because they may be the only remaining indication of transverse dune presence, and net dune migration direction once the dunefield is stabilized and in a final evolutionary state.     

Shelf-margin clinoforms and prediction of deepwater sands

Early Eocene successions from Spitsbergen and offshore Ireland, showing well‐developed shelf‐margin clinoforms and a variety of deepwater sands, are used to develop models to predict the presence or absence of turbidite sands in clinoform strata without significant slope disturbance/ponding by salt or mud diapers. The studied clinoforms formed in front of narrow to moderate width (10–60 km) shelves and have slopes, 2–4°, that are typical of accreting shelf margins. The clinoforms are evaluated in terms of both shelf‐transiting sediment‐delivery systems and the resultant partitioning of the sand and mud budget along their different segments. Although this sediment‐budget partitioning is controlled by sediment type and flux, shelf width and gradient, process regime on the shelf and relative sea‐level behaviour, the most tell‐tale or predictive signs in the stratigraphic record appear to be (1) sediment‐delivery system type, (2) degree of shelf‐edge channelling and (3) character of shelf‐edge trajectory through time. The clinoform data sets from the Porcupine Basin (wells and 3‐D seismic) and from the Central Basin on Spitsbergen (outcrops) suggest that river‐dominated deltas are the most efficient delivery systems for dispersing sand into deep water beyond the shelf‐slope break. In addition, low‐angle or flat, channelled shelf‐edge trajectories associate with co‐eval deepwater slope and basin‐floor sands, whereas rising trajectories tend to associate with muddy slopes and basin floors. Characteristic features of the shelf‐edge, slope and basin‐floor segments of clinoforms for these trajectory types are documented. Seismic lines along the slope to basin‐floor transects tend to show apparent up‐dip sandstone pinchouts, but most of these are likely to be simply sidelap features. Dip lines aligned along the axes of sandy fairways show that stratigraphic traps are unlikely, unless slope channels become mud‐filled or are structurally partitioned. Another feature that is prominent in the data sets examined is the lack of slope onlap. During the relative rise of sea level back up to the shelf, the clinoform slopes are generally mud‐prone and they are characteristically aggradational.     

A new tool for modeling dune field evolution based on an accessible, GUI version of the Werner dune model

Research into aeolian dune form and dynamics has benefited from simple and abstract cellular automata computer models. Many of these models are based upon a seminal framework proposed by Werner (1995). Unfortunately, most versions of this model are not publicly available or are not provided in a format that promotes widespread use. In our view, this hinders progress in linking model simulations to empirical data (and vice versa). To this end, we introduce an accessible, graphical user interface (GUI) version of the Werner model. The novelty of this contribution is that it provides a simple interface and detailed instructions that encourage widespread use and extension of the Werner dune model for research and training purposes. By lowering barriers for researchers to develop and test hypotheses about aeolian dune and dune field patterns, this release addresses recent calls to improve access to earth surface models.     

布古里沙漠部分地区风沙环境特征分析

布古里沙漠位于喀什绿洲和叶尔羌河绿洲之间,具有独特的地貌特征和风沙环境特征。通过对布古里沙漠部分地区的气象资料分析和野外实地风沙观测,对其风沙环境特征进行了分析。结果表明：布古里沙漠的沙粒平均粒径是0.16 mm,起沙时间集中在每年的4～9月,风向主要是西北风和东北风,偏西北风略强;在2 m高处测量的裸露沙面起动风速的是3.0 m/s,植被覆盖率为7%,起动风速为5.2 m/s,植被覆盖率为14%,起动风速为6.8 m/s;当平均风速为6.7 m/s时,气流输运沙子主要在近地表面0～10 cm,,风沙流中含沙量随垂直高度呈指数衰减,给出了风沙流的含沙量随垂直高度分布的相关方程和参数。     

固定沙丘风蚀坑风沙动力学观测研究

风蚀坑是固定沙丘活化的标志,也是沙漠化的首要环节。本文利用三杯风速仪、风向标及阶梯式集沙仪,对浑善达克沙地南缘固定沙丘风蚀坑的气流及输沙进行了观测。结果表明,气流进入风蚀坑后,经历了扩散减速—辐合加速—分离减速—逐渐恢复的过程。入风方向的微小变化、地形及植被导致风蚀坑气流结构、强度及输沙模式趋于复杂。与轴线平行（< 10°）的纵向气流使侵蚀坑内减速区西移,风速及输沙率由坑底向两侧壁及积沙区增加;与轴线斜交（≥ 10°）的气流使减速区东移,气流沿两侧壁向东加速及输沙。积沙区顶部的气流汇集与植被的作用使其加积增高。气流—形态相互作用使风蚀坑加深和纵向延伸并伴随侧向扩展。     

Effects of sand burial on dune plants: a review

Burial of different growth stages of plants （e.g., adult plants, seedlings and seeds） is frequent in dune ecosystems. The soil micro-environment, which differs from surface conditions, influences the survival and growth of dune plants. To sum up knowledge about the survival mechanisms of plants under sand burial and to promote practical rehabilitation of dune vegetation, we reviewed relevant published literature and concluded that： （1） Focus in recent years has been on impacts of sand burial on seed germination and seedling emergence. Generally, shallow burial increased seed germination and seedling emergence, but deeper burial was negative. Buried at the same depth, large seeds showed higher germination and seedling emergence rates, attributed to larger energy reserves. （2） Survival, growth and reproduction rates of dune plants show plasticity in response to sand burial. Long-term deep burial is fatal because it creates a physical barrier which overcomes the vertical growth of plants, reduces photosynthetic leaf area, and limits oxygen availability to roots. Modest burial, on the other hand, is advantageous for growth and reproduction of many dune plants, due to protection from excessive temperature and drought. （3） There are few reports concerning effects of sand burial on plant physiology, but a limited number of studies indicate that partial burial increases water use efficiency, chlorophyll content, transpiration rate and net photosynthetic rates. The antioxidant protective enzyme system and osmolyte balance were reported to be involved in the mechanisms of dune plant resistance to burial.     

Influential factors on the repose angle of desert sands

The repose angle is one of the most significant macroscopic parameters in describing the behavior of granular materials. Under a static condition, the repose angle is the steepest angle at which sediment particles can rest without motion. In this paper, we use existing data and aeolian physics to analyze the main factors that influence the repose angle of sand dunes, and we investigate different repose angles involving various states and types of materials. We have determined that different factors have differential influence on the magnitude of the repose angle. Our results show that for powdery (<400-μm diameter) desert sands, the main influential factor on the magnitude of repose angle is the molecular force among particles. Particle size does not influence the repose angle of desert sands directly, but has an indirect impact by affecting the grit sphericity and surface roughness, of which the grit sphericity acts as a major factor. Even at the same average particle size, the repose angle differs with different grain compositions. Furthermore, with increasing unevenness in grain composition, the repose angle increases correspondingly. Sand texture also has a direct influence on the repose angle of desert sands. In two sand samples having the same grain composition but different textures, the repose angles may be different. Water content has a stronger influence on the repose angle than any other factor. However, the relationship between the repose angle and water content is not a simple direct proportion. In fact, with increasing water content, the repose angle first increases and then decreases. These research results will be useful for understanding the mechanisms of dune transport, variations of dune morphology, and the stability and fluidity of dune sands.     

海岸沙丘系统脆弱性评价研究进展与展望

海岸沙丘系统脆弱性评价揭示海岸沙丘系统脆弱性的基本特征,为海岸沙丘保护与利用提供重要依据,是海岸沙丘研究近期备受关注的一个重要方面。论文基于国内外海岸沙丘系统脆弱性评价研究相关概念、发展历程、评价指标及技术方法等的回顾,概括了其在概念内涵深化、指标体系完善、脆弱性因子辨识、技术方法发展以及评价结果应用等方面的主要进展;并针对当前概念定义难以共识、指标体系争议较大、评价方法存在局限性和理论基础略显薄弱等研究不足,提出明晰相关概念、完善指标体系、改进评价方法、强化机理研究及增强趋势研判等海岸沙丘系统脆弱性近期研究的主要方向。     

Sand dune movement in the Victoria Valley, Antarctica

We use vertical aerial photographs and LiDAR topographic survey data to estimate dune migration rates in the Victoria Valley dunefield, Antarctica, between 1961 and 2001. Results confirm that the dunes migrated an average of 1.5 m/year. These values are consistent with other estimates of dune migration from cold climate deserts and are significantly lower than estimates from warm deserts. Dune migration rates are retarded by the presence of entrained ice, soil moisture and a reversing wind regime. Dune absorption, merging and limb extension are apparent from the time-series images and account for significant changes in dune form and the field-scale dune pattern. Dune-field pattern analysis shows an overall increase in dune-field organization with an increase in mean dune spacing and a reduction in total crest length and defect density. These data suggest that dunes in other cold desert environments on Earth, Mars or Titan, that may also have inter-bedded frozen laminae, still have the potential to migrate and organize, albeit at lower rates than dunes in warm deserts.     

Variation between bee communities on a sand dune complex in the Great Basin Desert,North America: Implications for sand dune conservation

Sand dunes across the Mojave and Great Basin Deserts house rich bee communities. The pollination services these bees provide can be vital in maintaining the diverse, and often endemic, dune flora. These dune environments, however, are threatened by intense off-highway vehicle (OHV) use. Conservation efforts adopted by land managers often consist of setting aside a portion of a dune system that is off-limits to OHV use, but little work has been done showing the extent to which this protects native bee communities. A two-year study of bee communities on a Great Basin sand dune complex in Dugway Proving Ground located in northwestern Utah revealed low similarity index values between closely situated collecting plots (1–40 km apart). Similarity values ranged from 0.13 to 0.70 for species composition, and from 0.07 to 0.57 when similarity was weighted by abundance. Distance between plots had no significant relationship to similarity when richness and abundance were considered. Bee similarity between plots was significantly correlated with floral similarity. These results indicate that dune conservation strategies that preserve “representative” portions of dune systems may be insufficient to protect bees and the pollination services they provide.     

Wind velocity and sand transport on a barchan dune

We present measurements of wind velocity and sand flux performed on the windward side of a large barchan dune in Jericoacoara, northeastern Brazil. From the measured profile, we calculate the air shear stress using an analytical approximation and treat the problem of flow separation by an heuristic model. We find that the results from this approach agree well with our field data. Moreover, using the calculated shear velocity, we predict the sand flux according to well-known equilibrium relations and with a phenomenological continuum saltation model that includes saturation transients and thus allows for nonequilibrium conditions. Based on the field data and theoretical predicted results, we indicate the principal differences between saturated and nonsaturated sand flux models. Finally, we show that the measured dune moves with invariant shape and predict its velocity from our data and calculations.