Wind erosion from military training lands in the Mojave Desert, California, U.S.A.

Military training activities reduce vegetation cover, disturb crusts, and degrade soil aggregates, making the land more vulnerable to wind erosion. The objective of this study was to quantify wind erosion rates for typical conditions at the Marine Corps Air Ground Combat Center, Twentynine Palms, CA, U.S.A. Five Big Spring Number Eight (BSNE) sampler stations were installed at each of five sites. Each BSNE station consisted of five BSNE samplers with the lowest sampler at 0·05 m and the highest sampler at 1·0 m above the soil surface. Once a month, sediment was collected from the samplers for analysis. Occurrence of saltating soil aggregates was recorded every hour using Sensits, one at each site. The site with the most erosion had a sediment discharge of 311 kg m⁻¹ over a period of 17 months. Other sites eroded much less because of significant rock cover or the presence of a crust. Hourly sediment discharge was estimated combining hourly Sensit count and monthly sediment discharge measured using BSNE samplers. More simultaneously measured data are needed to better characterize the relationship between these two and reconstruct a detailed time-series of wind erosion. This measured time-series can then be used for comparison with simulation results from process-based wind erosion models such as the Wind Erosion Prediction System (WEPS), once it has been adapted to the unique aspects of military lands.     

库鲁克沙漠风沙地貌与沙丘移动

库鲁克沙漠位于塔里木河下游以东,是塔克拉玛干沙漠的重要组成部分。利用风况资料和Google Earth卫星影像,对该沙漠的风沙地貌及其移动特征进行分析。结果表明:库鲁克沙漠风能环境属于低至中等;合成输沙势方向为西南至西南偏西方向;方向变率属于中等。具有风积和风蚀两种地貌类型,风积地貌类型主要包括平沙地、灌丛沙丘、新月形沙垄、新月形沙丘及沙丘链、复合新月形沙丘和复合型沙丘链,风蚀地貌类型主要为雅丹。沙漠西部新月形沙丘的移动方向为西南偏西方向,与当地合成风向大体一致。沙丘移动速率为9.5~37.8 m·a^-1,呈现明显的空间差异,主要取决于当地风况、沙丘高度和沙丘密度等因素,与沙丘高度和沙丘密度呈指数负相关关系。沙丘的形成发育及其移动是由多种因素相互作用的复杂过程,而这种复杂性塑造了丰富的风沙地貌类型及其区域差异性。     

Relationship between erosion and sediment yield in drainage basins of loess gully-hilly areas

From a long-term point of view, the balance between erosion and sediment yield in a drainage system can basically realize, i.e., the delivery ratio can be close to 1. However, substantial variations among individual rainfall events or between annual delivery ratio exist, causing frequent sediment retaining or re-erosion and re-delivery of the retained sediments in a short period of time. Thus the delivery ratio will be < 1 or > 1. The sediment delivery ratio is closely related to the spatial distribution of rainfall and magnitude of rise and fall of peak flood and that of runoff depth in the drainage system. Delivery ratio of single event in a drainage system and changes of delivery capacity of silt-laden runoff in various classes of gullies can be expressed by transformation mechanism of shear force of a single rainstorm event with flood resulting from increase and decrease of peak flood per unit area.     

Relationship between erosion and sediment yield in drainage basins of loess gully-hilly areas

From a long-term point of view, the balance between erosion and sediment yield in a drainage system can basically realize, i.e., the delivery ratio can be close to 1. However, substantial variations among individual rainfall events or between annual delivery ratio exist, causing frequent sediment retaining or re-erosion and re-delivery of the retained sediments in a short period of time. Thus the delivery ratio will be < 1 or > 1. The sediment delivery ratio is closely related to the spatial distribution of rainfall and magnitude of rise and fall of peak flood and that of runoff depth in the drainage system. Delivery ratio of single event in a drainage system and changes of delivery capacity of silt-laden runoff in various classes of gullies can be expressed by transformation mechanism of shear force of a single rainstorm event with flood resulting from increase and decrease of peak flood per unit area.     

库姆塔格沙漠风沙地貌遗产的旅游开发

对库姆塔格沙漠风沙地貌遗产进行旅游开发,既有利于“大敦煌”地区人-地关系的和谐演进,又有利于全面推进“大敦煌”地区旅游业的可持续发展。应用观察法、描述法、系统调查分析法等定性研究方法,在阐述库姆塔格沙漠风沙地貌遗产旅游开发意义的基础上,建设性地提出将库姆塔格沙漠风沙地貌遗产开发为旅游产品、旅游商品和旅游节事的途径、方式和方法。最后,根据风沙地貌特征和旅游发展需要,指出对库姆塔格沙漠风沙地貌遗产进行旅游开发时应该注意的生态环境保护、旅游形象和安全管理、基础设施建设等问题。     

Nest site characteristics and nesting success of the Western Burrowing Owl in the eastern Mojave Desert

We evaluated nest site selection at two spatial scales (microsite, territory) and reproductive success of Western Burrowing Owls (Athene cunicularia hypugaea) at three spatial scales (microsite, territory, landscape) in the eastern Mojave Desert. We used binary logistic regression within an information-theoretic approach to assess factors influencing nest site choice and nesting success. Microsite-scale variables favored by owls included burrows excavated by desert tortoise (Gopherus agassizii), burrows with a large mound of excavated soil at the entrance, and a greater number of satellite burrows within 5 m of the nest burrow. At the territory scale, owls preferred patches with greater cover of creosote bush (Larrea tridentata) within 50 m of the nest burrow. An interaction between the presence or absence of a calcic soil horizon layer over the top of the burrow (microsite) and the number of burrows within 50 m (territory) influenced nest site choice. Nesting success was influenced by a greater number of burrows within 5 m of the nest burrow. Total cool season precipitation was a predictor of nesting success at the landscape scale. Conservation strategies can rely on management of habitat for favored and productive nesting sites for this declining species.     

Sediment deposition in the flood plain of Stemple Creek Watershed, northern California

Over the past 150 years, major land use changes have occurred in the Stemple Creek Watershed in northern California that have caused erosion to move soils from the upland to the flood plain, stream channels, and the bay. The purpose of this study is to document the recent (1954 to present) sediment deposition patterns in the flood plain area adjacent to Stemple Creek using the ¹³⁷Cesium technique. Sediment deposition ranged from 0.26 to 1.84 cm year⁻¹ for the period from 1964 to 2002 with an average of 0.85±0.41 cm year⁻¹. Sediment deposition rates were higher for the 1954 to 1964 period with a range of 0.31–3.50 cm year⁻¹ and an average of 1.29±1.04 cm year⁻¹. These data indicate that sediment deposition in the flood plain has decreased since the middle 1950s, probably related to reduction in row crop agriculture and an increase in pasturelands. This study shows that the flood plains in the Stemple Creek Watershed are a significant sink for the soils being eroded from the upland area. Given the significance of the flood plain for trapping eroded materials before they reach the stream channels or the bay, efforts need to be made to manage these flood plain areas to insure that they do not change and become a source rather than a sink for eroded materials as improved management practices on the upland areas reduce sediment input to the flood plain.     

巴丹吉林沙漠沙山粒度组成与沙山地貌分带

为查明巴丹吉林沙漠东南部沙山的成因与发育机制,在沙山密集分布的中心地区选择典型高大沙山作为研究对象,将单个沙山的物质组成与地貌分带相结合进行系统、定量的研究.通过粒度分析获得了沙山不同剖面、不同部位沉积物的粒度组成和各粒级含量的变化等数据,并进一步探讨了粒度组成和含量变化与沙山地貌分带、形成风动力条件之间的相互关系.得出以下主要结论:1.巴丹吉林沙漠沙山粒度组成为粗粉砂、极细砂、细砂、中砂、粗砂.其中细砂含量最高,中砂、粗砂次之,极细砂和粗粉砂含量均较少.2.沙山迎风坡表层沉积物的粒度比迎风坡下层和背风坡表层要粗,其搬运介质的平均动能也最大.3.从沙山坡脚到坡顶粒度组成均呈现由粗变细的趋势,这是由它们的形成过程和受到的动力作用存在差异决定的.4.沙山迎风坡不同部位的坡度、沙丘类型与分布在纵向上存在明显差异,可将其分为风蚀粗化的平沙洼地带、稀疏简单的新月形沙丘或沙丘链带、密集叠置的新月形沙丘及沙丘链带、陡峭的主峰带等4个地貌带.5.组成沙山的风沙物质不是一次搬运到达沙山中上部的,而是经过了多次的风力搬运阶段才达到的.     

库姆塔格沙漠地表物质组成、来源和风化过程

通过对库姆塔格沙漠地表沉积物样品进行重矿物和主量元素分析,获得了其矿物和元素组成特征:矿物种类多,绿帘石和角闪石含量为主;化学组成上以Si、Al为主,和上陆壳平均化学组成相比,除Si、Ca外都有一定的亏损,Fe、Mg、Ca、P、Ti、Mn等元素的变异系数较高。库姆塔格沙漠地表沙物质组成特征与阿尔金山北麓出露的岩石和冲、洪积扇物质组成基本一致,与塔克拉玛干沙漠也有很大的共性,反映了库姆塔格沙漠地表沙物质主要来源于阿尔金山。沙漠北区强烈的东北风将阿奇克谷地和疏勒河下游的河湖相沉积物搬运至沙漠腹地,构成另一个重要的沙物质来源。A-CN-K图解揭示了库姆塔格沙漠地表物质化学风化程度很低,处于较弱的去Na、Ca阶段,其他元素未发生明显的化学风化或迁移;A-CNK-FM图解表明,库姆塔格沙漠地表物质在搬运、沉积过程中Fe、Mg等元素发生显著分异,其原因主要是铁镁质矿物由于磨损、分选作用遭破碎和风化,使粒度较粗的沙漠沙Fe、Mg等元素相对亏损。     

Impacts of interrelated biotic and abiotic processes during the past 125 000 years of landscape evolution in the Northern Mojave Desert, Nevada, USA

Interrelated, biotic (flora and fauna) and abiotic (pedogenesis and hydrology) processes were examined at four sites (30, and approximately 1000–3000, 7000–12 000, and 125 000 years before present) in the northern Mojave Desert. Data collected at each included floral and faunal surveys; soil texture, structure, and morphology; and soil hydraulic properties. Separate measurements were made in shrub undercanopy and intercanopy microsites. At all sites, shrubs made up greater than 86 percent of total perennial cover, being least on the youngest site (4 percent) and most on the 7000–12 000-year-old site (31 percent). In the intercanopy, winter annual density was highest on the 1000- to 3000-year-old site (249 plants/m²) and lowest on the oldest site (4 plants/m²). Faunal activity, measured by burrow density, was highest on the 1000–3000- and 7000–12 000-year-old sites (0.21 burrows/m²) and density was twice as high in the undercanopy versus the intercanopy. Burrow density was lower at the two oldest sites, although density was not statistically greater in the undercanopy than intercanopy. At the older sites, the soil water balance was increasingly controlled by Av horizons in intercanopy soils in which saturated hydraulic conductivity (K_sat) decreased 95 percent from the youngest to the oldest site. No significant reduction in K_sat in undercanopy soils was observed. Decreases in the intercanopy sites correlated with decreases in annual plant density and bioturbation, suggesting these processes are interrelated with surface age.     

Mineralogical maturity in dunefields of North America, Africa and Australia

Studies of dunefields in central and western North America show that mineralogical maturity can provide new insights into the origin and evolution of aeolian sand bodies. Many of the world's great sand seas in Africa, Asia and Australia are quartz-dominated and thus can be considered to be mineralogically mature. The Algodones (California) and Parker (Arizona) dunes in the southwestern United States are also mature, but have inherited a high degree of mineralogical maturity from quartz-rich sedimentary rocks drained by the Colorado River. In Libya, sediments of the Zallaf sand sea, which are almost pure quartz, may have originated in a similar fashion. The Fort Morgan (Colorado) and Casper (Wyoming) dunefields in the central Great Plains of North America, and the Namib sand sea of southern Africa have an intermediate degree of mineralogical maturity because their sources are large rivers that drained both unweathered plutonic and metamorphic rocks and mature sedimentary rocks. Mojave Desert dunefields in the southwestern United States are quite immature because they are in basins adjacent to plutonic rocks that were their sources. Other dunefields in the Great Plains of North America (those in Nebraska and Texas) are more mature than any possible source sediments and therefore reflect mineralogical evolution over time. Such changes in composition can occur because of either of two opposing long-term states of the dunefield. In one state, dunes are stable for long periods of time and chemical weathering depletes feldspars and other weatherable minerals in the sediment body. In the other state, which is most likely for the Great Plains, abrasion and ballistic impacts deplete the carbonate minerals and feldspars because the dunes are active for longer periods than they are stable.     

Spatial distribution of surface conditions and runoff generation in small arid watersheds, Zin Valley Badlands, Israel

High rill density may be regarded as indicative of frequent and integrated runoff along a drainage network. However, field observations of soil development and rill geometry in small, first-order catchments (0.1 to 1 ha) of the Zin Valley Badlands, northern Negev, Israel, suggest a pattern of partial area contribution and frequent flow discontinuities along hillslopes and channels. Changing soil properties, associated with an increase of slope angle and slope length, appear to be responsible for high infiltration on the slopes, leading to nonuniform runoff generation within small drainage basins. Runoff observation, sprinkling tests, and soil analysis along ridges and sideslopes were carried out to test this hypothesis. The results confirmed that infiltration capacity on the sideslopes is significantly higher than on the ridges. Under current rainfall conditions, only extreme rainfall intensities are sufficient to generate runoff along entire slopes. The discontinuous nature of most runoff events causes erosion on ridges and deposition on slopes, which enhances soil development on the valley sideslopes, creating a positive feedback on infiltration rate and depth. This demonstrates that the links between within-storm rainfall conditions and spatial distribution of soil characteristics have to be incorporated into our understanding of landscape development in badlands.     

Effectiveness of grade-control structures in reducing erosion along incised river channels: the case of Hotophia Creek, Mississippi

Herein, we undertake a geomorphological analysis in which spatial and temporal trends of bed and bank erosion along an 18-km length of Hotophia Creek, Mississippi, are estimated for the period between 1961 and 2050. The evaluation was undertaken for two scenarios of channel response to channelization during 1961–1963. One scenario represents the ‘actual’ response of the channel and includes the effects of installing a series of grade-control structures (GCS) between 1980 and 1996, while the other represents a hypothetical scenario in which the channel is left to adjust naturally. This allows the effectiveness of GCS in reducing in-channel erosion to be assessed. The analysis relies on the availability of channel survey data to develop empirical bed and bank response models for each adjustment scenario, supplemented by bank stability modelling to predict future rates of bank erosion. Results indicate that channel erosion rates decline nonlinearly with respect to time since 1961, for both adjustment scenarios. However, by the year 2050, the “with” GCS adjustment scenario results in the cumulative removal of some 663,000 (9%) extra tonnes of sediment relative to the “without” GCS scenario. Most (63%) of this excess is derived from enhanced bed erosion during 1976–1985 and 1985–1992, with the remainder derived from increased bank erosion during 1985–1992. Detailed analysis of the patterns of erosion and deposition, and their association with the GCS, provides evidence to support the view that GCS installed along Hotophia Creek have, for the most part, been ineffective in reducing channel erosion rates. This is because the GCS were installed too late to prevent bed degradation, caused by the 1961–1963 channelization, migrating upstream. In addition, some structures have disrupted the downstream transmission of bed material from eroded reaches upstream, exacerbating bed degradation and bank erosion in incised reaches downstream.     

Sediment concentration changes in runoff pathways from a forest road network and the resultant spatial pattern of catchment connectivity

Hydrological connectivity is a term often used to describe the internal linkages between runoff and sediment generation in upper parts of catchments and the receiving waters. In this paper, we identify two types of connectivity: direct connectivity via new channels or gullies, and diffuse connectivity as surface runoff reaches the stream network via overland flow pathways. Using a forest road network as an example of a landscape element with a high runoff source strength, we demonstrate the spatial distribution of these two types of linkages in a 57 km² catchment in southeastern Australia. Field surveys and empirical modelling indicate that direct connectivity occurs primarily due to gully development at road culverts, where the average sediment transport distance is 89 m below the road outlet. The majority of road outlets were characterised by dispersive flow pathways where the maximum potential sediment transport distance is measured as the available hillslope length below the road outlet. This length has a mean value of 120 m for this catchment. Reductions in sediment concentration in runoff plumes from both pathways are modelled using an exponential decay function and data derived from large rainfall simulator experiments in the catchment. The concept of the volume to breakthrough is used to model the potential delivery of runoff from dispersive pathways. Of the surveyed road drains (n=218), only 11 are predicted to deliver runoff to a stream and the greatest contributor of runoff occurs at a stream crossing where a road segment discharges directly into the stream. The methodology described here can be used to assess the spatial distribution and likely impact of dispersive and gullied pathways on in-stream water quality.     

川中丘陵区和三峡地区小流域侵蚀产沙的塘库沉积137Cs断代

选择川中丘陵区和三峡地区四川盐亭、南充和重庆开县的4个小流域,采集塘库沉积泥沙137Cs样品,确定了1963年以来塘库淤沙量,并据此分析了流域输沙模数和侵蚀模数。研究表明,开县春秋沟的淤沙模数最高,为1869t.km-2.a-1;盐亭武家沟和集流沟分别为701t.km-2.a-1和710 t.km-2.a-1;南充天马湾沟为566 t.km-2.a-1。对小流域地貌特征的分析和谷地水田取样结果表明,除塘库淤积区外,各小流域谷地内基本无泥沙淤积。因此,除南充天马湾沟按现有水面面积作为淤积面积求算的淤沙模数明显偏小外,其他小流域的塘库淤沙模数基本可以表征各研究小流域的侵蚀模数。对研究小流域侵蚀产沙影响因素的分析表明,除降雨和土地利用状况外,地形起伏、土壤抗蚀性及岩层产状也是三地侵蚀程度差异的重要原因。     

Holocene history of lacustrine and marsh sediments in a dune-blocked drainage, Southwestern Nebraska Sand Hills, U.S.A.

As many as 2500 interdune lakes lie within the Nebraska Sand Hills, a 50000 km stabilized sand sea. The few published data on cores from these lakes indicate they are typically underlain by less than two m of Holocene lacustrine sediments. However, three lakes in the southwestern Sand Hills, Swan, Blue, and Crescent, contain anomalously thick marsh (peat) and lacustrine (gyttja) sediments. Swan Lake basin contains as much as 8 m of peat, which was deposited between about 9000 and 3300 years ago. This peat is conformably overlain by as much as 10.5 m of gyttja. The sediment record in Blue lake, which is 3 km downgradient from Swan lake, dates back to only about 6000 years ago. Less than two m of peat, which was deposited from 6000 to 5000 years ago, is overlain by 12 m of gyttja deposited in the last 4300 years. Crescent Lake basin, one km downgradient from Blue Lake, has a similar sediment history except for a lack of known peat deposits. Recently, a 8-km long segment of a paleovalley was documented running beneath the three lakes and connecting to the head of Blue Creek Valley. Blockage of this paleovalley by dune sand during two arid intervals, one shortly before 10500 yr BP and one in the mid-Holocene, has resulted in a 25 m rise in the regional water table. This made possible the deposition of organic-rich sediment in all three lakes. Although these lakes, especially Swan, would seem ideal places to look for a nearly complete record of Holocene climatic fluctuations, the paleoclimatic record is confounded by the effect dune dams have on the water table. In Swan Lake, the abrupt conversion from marsh to lacustrine deposition 3300 years ago does not simply record the change to a wetter regional climate; it reflects the complex local hydrologic changes surrounding the emplacement and sealing of dune dams, as well as regional climate.     

Modelling the runoff-sediment yield relationship using a proportional function in hilly areas of the Loess Plateau, North China

Based on data observed at the 12 small watersheds in hilly areas of the Loess Plateau, North China, the relationship between event runoff volume and sediment yield is examined. The results reveal that the runoff-sediment yield relationship at the inter-event timescale is mainly determined by the runoff-sediment concentration relationship at the intra-event timescale. In the study area, the sediment concentration tends to be stable when the flow discharge exceeds a certain critical value. Many factors that are important for determining the characteristics of low-magnitude events, such as flow discharge, particle size of fluvial sediment, and accumulation of loose material on land surfaces prior to a rainstorm, appear to have little importance for high-magnitude events. Consequently, mean sediment concentration tends to be stable for large flood events, suggesting a strong similarity between the two flow-sediment relationships at inter-and intra-event temporal scales. Furthermore, a proportional function is proposed to predict event sediment yield, and the correspondence between the predicted and observed sediment yields is examined. The performance of the model is good for high-magnitude events, especially extreme events. The applicability of the proposed model at the annual timescale is also discussed.     

Factors affecting runoff and sediment yield on the semiarid loess area in Northern Shaanxi Province,China

The semiarid loess area in north Shaanxi Province is one of the most serious areas of water erosion in China. The Chinese government initiated the project “Grain-for-Green” for soil erosion control in 1999, with significant effect. Vegetation, rainfall, soil, and topography are the most dominant natural factors affecting soil erosion; therefore, the aim of this research was to investigate the effects of these four factors on runoff and soil loss at the runoff-plot scale over five years and use the Gray relational analysis methods to compare the impacts of these factors. Five runoff-measuring sites were established in five different vegetation types. The results show that the relative impacts of the four factors on runoff were: rainfall > soil > topography > vegetation, and the relative impacts of the factors on sediment yield were soil > runoff > rainfall > topography > vegetation. We also analyzed the weights of these four factors on runoff and sediment yield during the wettest year alone. For that year, the relative weights of the factors on runoff were topography > rainfall > soil > vegetation, and the relative weights of the factors on sediment yield were runoff > soil > rainfall > topography > vegetation.     

不同坡面植被空间布局对坡沟系统产流产沙影响的实验

植被在有效控制水土流失、改善生态环境中具有重要作用。为探讨坡面不同植被覆盖度、不同植被空间布局对坡沟系统侵蚀产沙的影响,以4 m长坡面(坡度为20°)和3 m长沟坡(坡度为50°)组成的坡沟系统为研究对象,采用不同放水流量(3.2 L/min、5.2 L/min)的放水冲刷实验,研究了不同放水流量、不同植被覆盖度、不同植被布设部位对坡-沟系统及沟坡侵蚀产沙的影响。结果表明,在实验条件下,不同植被布设部位在相同放水流量、相同植被覆盖度条件下对坡沟系统侵蚀产沙有明显影响,而对产流量无明显影响;沟坡部分侵蚀产沙量不随坡面植被覆盖度的增大而减小,相反呈增大趋势。说明在实验条件下,对坡沟系统而言,仅在坡面部分布设植被,尽管能在一定程度上减少坡沟系统侵蚀产沙,但并不能有效减小沟坡部分的侵蚀产沙,甚至引起沟坡部分侵蚀产沙的增大。因此,水土流失治理过程中采取有效措施进行坡沟兼治将是减少水土流失的有效手段。