Invasions in Marine Communities: Contrasting Species Richness and Community Composition Across Habitats and Salinity

While many studies of non-native species have examined either soft-bottom or hard-bottom marine communities, including artificial structures at docks and marinas, formal comparisons across these habitat types are rare. The number of non-indigenous species (NIS) may differ among habitats, due to differences in species delivery (trade history) and susceptibility to invasions. In this study, we quantitatively compared NIS to native species richness and distribution and examined community similarity across hard-bottom and soft-sediment habitats in San Francisco Bay, California (USA). Benthic invertebrates were sampled using settlement panels (hard-bottom habitats) and sediment grabs (soft-bottom habitats) in 13 paired sites, including eight in higher salinity areas and five in lower salinity areas during 2 years. Mean NIS richness was greatest in hard-bottom habitat at high salinity, being significantly higher than each (a) native species at high salinity and (b) NIS richness at low salinity. In contrast, mean NIS richness in soft-bottom communities was not significantly different from native species richness in either high- or low-salinity waters, nor was there a difference in NIS richness between salinities. For hard-bottom communities, NIS represented an average of 79% of total species richness per sample at high salinity and 78% at low salinity, whereas the comparable values for soft bottom were 46 and 60%, respectively. On average, NIS occurred at a significantly higher frequency (percent of samples) than native species for hard-bottom habitats at both salinities, but this was not the case for soft-bottom habitats. Finally, NIS contributed significantly to the existing community structure (dissimilarity) across habitat types and salinities. Our results show that NIS richness and occurrence frequency is highest in hard-bottom and high-salinity habitat for this Bay but also that NIS contribute strongly to species richness and community structure across each habitat evaluated.     

The effect of human disturbance on foraging behavior and habitat use in piping plover (Charadrius melodus)

Piping plovers breed in coastal areas where they experience intense competition with man. I studied habitat use (using transects) and foraging behavior (using focal animals) at three habitats on each of three nesting beaches over a 2-yr period (1988–1989) in New Jersey, USA, to understand how plovers use space. Piping plovers forage along in tidal oceanfront, in the dunes, and in backbays, and their relative use of tehse habitats partially depends on the presence of people. Within each habitat the plovers select sites that contain fewer people than the habitat as a whole. The time devoted to vigilance (when they are not searching for food) is directly related to the number of people near them, and to the overall human use of that habitat. Thus, in habitats with few people the plovers can spend 90% of their foraging time actively searching for prey and feeding, whereas on beaches with many people they may spend less than 50% of their foraging time in direct feeding behaviors. A diversity of habitats allows the birds to move between habitats to minimize interactions with people and maximize the time devoted to foraging. The results suggest that it is critical to maintain high habitat diversity in coastal environments to help mitigate competition with people.     

Inter‐annual variability of southerly winds in a coastal area of the Atacama Desert: implications for the export of aeolian sediments to the adjacent marine environment

The analysis of the aeolian content of marine cores collected off the coast of the Atacama Desert (Mejillones Bay, Chile) suggests that marine sediments can record inter‐annual to inter‐decadal variations in the regional southerly winds responsible for particle entrainment at the surface of the nearby desert. However, the establishment of a simple and direct correlation between the sediment and wind records is complicated by the difference of time scales between the erosion and accumulation processes. The aim of this work is to: (i) assess the inter‐annual variability of the surface winds responsible for the sand movements; and (ii) determine whether the integration over periods of several months completely smoothes the rapid changes in characteristics of the transported and deposited aeolian material. To accomplish this aim, 14 years of 10 m hourly wind speed, measured at the Cerro Moreno (Antofagasta) Airport between 1991 and 2003 and at the Orica Station between 2000 and 2004, were analyzed. For each year, the wind speed statistical distribution can be represented by a combination of two to three Weibull functions. Winds of the lowest Weibull mode are too weak to move the sand grains at the surface of the pampa; this is not the case for the intermediate mode and especially for the highest speed mode which are able to erode the arid surface and transport particles to the bay. In each individual year of the period of study, the highest speed mode only accounted for a limited number of strong erosion events. Quantitative analysis of the distribution of the friction velocities and of their impact on erosion using a saltation model suggests that, although all wind speeds above threshold produce erosion events, values around 0·45 m sec^?1 contribute less to the erosion flux. This gap allows separation of the erosion events into low and high saltation modes. The correlation (r = 0·997) between the importance of the third Weibull mode and the extent of higher rate saltation indicates that the inter‐annual variability of the erosion at the surface of the pampa, as well as the transport of coarse particles (>100 μm), are directly related to inter‐annual variations in the prevalence of the strongest winds. Finally, a transport and deposition model is used to assess the possible impact of the wind inter‐annual variability on the deposition flux of mineral particles in the bay. The results suggest that inter‐annual differences in the wind speed distributions have a quantifiable effect on the intensity and size‐distribution of this deposition flux. This observation suggests that a detailed analysis of the sediment cores collected from the bay could be used for reconstructing the inter‐annual variability of past winds.     

沙漠公路风沙土路基风蚀破坏试验研究

以沙漠公路风沙土路基为研究对象,通过室内风蚀风洞试验研究路基的风蚀破坏规律,以及路基不同断面对风沙流运动的影响。以路基高度、路基边坡坡率和路基宽度作为路基断面主要设计参数,研究不同路基断面下风沙流扰动、增速、减速、恢复的过程,以及路基周围风速流场的变化特征,分析路基病害较未病害时路基周围流场的变化。试验结果表明：路基高度和边坡坡率对风沙流运动的影响较大。随路基高度增加,路基对风沙流流场扰动增强,迎风坡坡顶处吹蚀破坏和背风坡坡底处堆蚀破坏越显著,在确定的路基边坡坡率下,路基模型高度为250 mm较模型高度为60 mm时,迎风坡坡顶风速增加1.13倍,背风坡坡底风速减小2.53倍,建议沙漠公路路基高度宜小于2.5 m。进一步,在确定的路基高度下,比较不同的边坡坡率对路基沿程风速的影响,发现当路基边坡坡率为1:1.75时,路基沿程风速变化不明显,沙漠公路风沙土路基不宜被风蚀破坏。     

Assessing the role of winter grazing in historic land degradation,Mývatnssveit,northeast Iceland

This paper assesses the contribution of historical and traditional winter grazing to long‐term land degradation in northeast Iceland. To do so, indicators of soil erosion from two contrasting historical winter grazing areas, set in a tephrochronological framework, are compared against their temporal and regional land degradation contexts. The observations made indicate distinctive and different landscape responses to historical winter grazing depending on location. In both study areas, there is an accelerated level of wind and water erosion with settlement at ca. A.D. 874 through to A.D. 1477. One of these areas had a subsequent reduction in erosion rates to considerably below the regional average, possibly as a result of adaptive land management; the second, more inherently sensitive area, is now subarctic desert. These findings confirm early land management practices as a major factor in Icelandic land degradation, they contribute to explanations of early settlement success and failure, and highlight the significance of historical approaches in addressing contemporary issues of land degradation and conservation responses. © 2004 Wiley Periodicals, Inc.     

Kitchen waste for Sporosarcina pasteurii cultivation and its application in wind erosion control of desert soil via microbially induced carbonate precipitation

Kitchen waste and wind erosion are two worldwide environmental concerns. This study investigated the feasibility of using kitchen waste for Sporosarcina pasteurii cultivation and its application in wind erosion control of desert soil via microbially induced carbonate precipitation (MICP). Enzymatic hydrolysis was adopted to improve the release and recovery of protein in kitchen waste for subsequent microorganism production. After conditions optimized, the maximum biomass concentration (OD₆₀₀) and urease activity of Sporosarcina pasteurii in the kitchen waste-based medium reached 4.19, and 14.32 mM urea min^?1, respectively, which were comparable to those obtained in conventional standard media. The harvested Sporosarcina pasteurii was then used to catalyze the precipitation of calcium carbonate in the desert soil, and its performance in wind erosion control was evaluated through wind tunnel tests. The microbially mediated calcium carbonate could significantly decrease wind erosion loss of the desert soil even after 12 wet–dry or freeze–thaw cycles. Scanning electron microscopy (SEM) with energy-dispersive X-ray (EDX) confirmed the bridge effect of calcium carbonate crystals in the soil matrix. The kitchen waste, as a cost-effective alternative nutrient for bacterial cultivation and carbonate precipitation, showed great potential for large-scale applications in wind erosion control of desert soils.

     

Dynamic processes acting on a longitudinal (seif) sand dune

ABSTRACT Field measurements were made on a longitudinal dune in the Sinai Desert in order to understand its morphology and dynamics. The field measurements contradicted the wind structure indicated by the helicoidal flow theory. Rather, it was found that winds coming from two basically different directions at different times and striking the dune obliquely were responsible for sand transport and erosion or deposition along the lee flank.
The essence of this mechanism is the deflection of the wind airflow on the lee flank of the dune to a direction parallel to the crest line. The occurrence of erosion or deposition depends upon the angle of incidence between the wind and the crest line. When this angle is < 40° the velocity of the deflected wind is higher than on the crest line or the windward flank and longitudinal sand transport occurs. When the angle is less acute (> 40°) the velocity of the deflected wind drops and deposition takes place on the lee flank.
The angle of incidence in each wind storm is changed intermittently between 30° and 100° along the dune because the dune meanders and because of the sinuous outline of the crest line. In this manner sand transport and erosion or deposition occurs along the lee flank depending on the angle of incidence between the wind and the crest line. As a result of the deflection of the wind the dune elongates at an average rate of more than 1 m per month. Peaks and saddles along the crest line advance at an average rate of 0.7 m per month.
The lack of uniformity in the effects of the wind on both sides of the dune creates a lack of uniformity in the rate of erosion and deposition. This can explain the formation of peaks along the crest line of the dune.     

Hidden Components in Tropical Seascapes: Deep-Estuary Habitats Support Unique Fish Assemblages

Tropical coastal seascapes are biodiverse and highly productive systems composed of an interacting mix of habitats. They provide crucial ecosystem services that support people’s livelihoods, yet key components of these seascapes remain unstudied. We know little about the deep (>2 m) subtidal areas of tropical estuaries, because, due to gear restrictions, there have been no detailed studies of the habitats they contain and the fish that use them. Consequently, potentially important functions and linkages with surrounding habitats remain unknown. Using unbaited videos, an approach capable of sampling the full breadth of benthic habitats and whole fish assemblages, we investigated patterns of fish occupancy of the deep subtidal habitats (2–20 m) in one of Australia’s largest tropical estuaries. We identified 19 taxa not previously recorded from estuaries of tropical eastern Australia, along with 36 previously identified estuary taxa. Three recognisable fish assemblages were associated with distinct benthic habitat types: open bottom fine sediment, seagrass and structurally complex rocky areas. In deep water, habitats often overlooked in shallow water become important, and there are sharp differences in habitat function. Deep subtidal habitats are potentially an important zone for direct interaction between estuary and marine fauna, with a range of consequences for intertidal habitat use and nursery ground functioning. The interface between marine areas and the shallow-water estuary may be richer and more complex than previously recognised.     

A wind tunnel simulation and field verification of desert dust deposition (Avdat Experimental Station, Negev Desert)

The deposition of natural dust in an area of 53 ha, situated in the northern Negev desert, is investigated in detail both in the wind tunnel (dust storm simulations over a topographic scale model) and in the field. The wind tunnel results and the field results show a high degree of agreement, indicating that scale-model simulation may be considered an important technique for future loess and desert research. More dust settles on windward slopes than on leeward slopes, which is in contradistinction with the widespread wind shadow concept. Air-flow separation zones immediately downwind of steep windward slopes have an important impact on dust deposition too. In the case of dust deposition on topographic scale models, a restricted height distortion of the model will not necessarily lead to serious problems. In addition, wind tunnel blockage percentages up to 13% may be allowed in order to obtain acceptable dust deposition patterns for the scale model. A mean gross dust deposition of about 200–250 g m^?2 year^?1 is calculated for the northern Negev desert for 1987. Thus, if the settled dust can be protected against erosion in the cultivated areas in the Negev, the dust content of the top soil will markedly increase with time. However, it has to be borne in mind that cultivation activities themselves may also contribute to a higher soil erosion and, hence, to a higher dust content in the atmosphere. At any rate, a higher dust content in the top soil will unquestionably have an important positive effect on agricultural yields. From the air dust concentration data and the dust deposition data, a deposition velocity of 4.7cms^?1 can be calculated for Avdat dust.     

Changes in Habitat Availability for Multiple Life Stages of Diamondback Terrapins (<Emphasis Type="Italic">Malaclemys terrapin</Emphasis>) in Chesapeake Bay in Response to Sea Level Rise

Global sea level rise (SLR) will significantly alter coastal landscapes through inundation and erosion of low-lying areas. Animals that display area fidelity and rely on fringing coastal habitats during multiple life stages, such as diamondback terrapins (Malaclemys terrapin Schoepff 1793), are likely to be particularly vulnerable to SLR-induced changes. We used a combination of empirical nest survey data and results from a regional SLR model to explore the long-term availability of known nesting locations and the modeled availability of fringing coastal habitats under multiple SLR scenarios for diamondback terrapin in the MD portion of Chesapeake Bay and the MD coastal bays. All SLR scenarios projected the rapid inundation of historically used nesting locations of diamondback terrapins with 25%–55% loss within the next 10 years and over 80% loss by the end of the century. Model trajectories of habitat losses or gains depended on habitat type and location. A key foraging habitat, brackish marsh, was projected to decline 6%–94%, with projections varying spatially and among scenarios. Despite predicted losses of extant beach habitats, future gains in beach habitat due to erosion and overwash were projected to reach 40%–600%. These results demonstrate the potential vulnerability of diamondback terrapins to SLR in Chesapeake Bay and underscore the possibility of compounding negative effects of SLR on animals whose habitat requirements differ among life stages. More broadly, this study highlights the vulnerability of species dependent on fringing coastal habitats and emphasizes the need for a long-term perspective for coastal development in the face of SLR.     

A methodology for the study of the relation between coastal cliff erosion and the mechanical strength of soils and rock masses

A methodology is proposed to make approximate estimates of the destructive force of waves at the bottoms of cliffs where no accurate bathymetric data are available, by means of correlation between the erosion rate of rocky coasts and the mechanical strength of soils and rock masses. The correlation used makes it possible to obtain a linear semi-logarithmic expression between the long-term average erosion rate (from an engineering standpoint) of coasts consisting of different lithologies, wave energy, and the uniaxial compressive strength of soils and rock masses forming the cliffs. The uniaxial compressive strength of soils consisting of landslide debris was measured using a pocket penetrometer and the Rock Mass index (RMi) method was used for rock masses. These methods were chosen after critical analysis of the methodologies currently available. The proposed approach was tested in the Cilento area of southern Italy, and in particular along a 6 km stretch of coast typified by rock masses and landslide debris that are particularly susceptible to erosion. This coastline is exposed to south-westerly waves which in deep water reach significant heights (between 1 and 3 m) and significant wave periods (between 4 and 7 s). Estimates of the coastal erosion rates were made by studying the variations, especially in restricted headland areas, occurring over two time spans, 30 and 45 years, respectively by comparing topographic maps and aerial photographs taken at different times. These comparisons give approximate indications of retreats of 15 m over the time span of 30 years (average erosion rate of 0.5 m year⁻¹) and of 35 m over the time span of 45 years (average erosion rate of ca 0.8 m year⁻¹). These data do have a local significance but clearly show how quick these processes sometimes are. Lastly, the study of a notch incised by wave action on a concrete sea wall built to protect a terrace made it possible to quantify the impact of erosion on concrete. It was possible to obtain RMi-values through field observations. Furthermore, it was possible to obtain the constants of the Hoek and Brown failure criterion using RMi. On the basis of RMi-values, the rock masses studied were defined as ‘moderately strong’ to ‘strong’ and, according to the Hoek and Brown criterion, as ‘poor’ to ‘fair’. A semilogarithmic linear relation was found between the strength of landslide debris, rock masses and concrete, as well as their respective long-term erosion. Consequently, a rough estimate of the destructive force of waves (ca 24 MPa) was calculated. This value is given by the product of the mean value of their hydraulic pressure for a non-dimensional constant which, in turn, takes into account the sandy-pebbly beach sediment at the foot of the cliffs that acts as an abrasive on the rock mass.     

Sand movement patterns in the Western Desert of Egypt: an environmental concern

Wind action is the most dominant agent for erosion and deposition in the vast Western Desert of Egypt. Analysis of wind data from seven meteorological stations distributed along the Western Desert reveals that this desert is characterized by high-energy wind environments along the northern and southern edges and low-energy wind environments throughout the rest of the desert. Accordingly, sand drift potential follows the pattern of wind energy. Maximum sand drift potential was observed at the southern edge (571 vector units, which equals 40 m³/m width/year). Sand drift direction was observed towards the southeast except at the southern part of the desert where the trend of sand movement was towards southwest. The major dune type recognized on satellite images was the simple linear type. Linear dunes are generally associated with bimodal wind regime. Rates of sand drift potential and sand dune migration were greatest at East of Owinate region at the extreme southern part of the desert. Measurements of crescentic sand dune advance from two satellite images reveal a maximum advance rate of about 9 m/year at the southern part of the desert. Dune movement creates potential hazard to the infrastructures in this open desert.     

Defining geo-habitats for groundwater ecosystem assessments: an example from England and Wales (UK)

Groundwater ecosystems comprising micro-organisms and metazoans provide an important contribution to global biodiversity. Their complexity depends on geology, which determines the physical habitat available, and the chemical conditions within it. Despite this, methods of classifying groundwater habitats using geological data are not well established and researchers have called for higher resolution habitat frameworks. A novel habitat typology for England and Wales (UK) is proposed, which distinguishes 11 geological habitats (geo-habitats) on hydrogeological principles and maps their distribution. Hydrogeological and hydrochemical data are used to determine the characteristics of each geo-habitat, and demonstrate their differences. Using these abiotic parameters, a new method to determine abiotic habitat quality is then developed. The geo-habitats had significantly different characteristics, validating the classification system. All geo-habitats were highly heterogeneous, containing both high quality habitat patches that are likely to be suitable for fauna, and areas of low quality that may limit faunal distributions. Karstic and porous habitats generally were higher quality than fractured habitats. Overall, 70% of England and Wales are covered by lower quality fractured habitats, with only 13% covered by higher quality habitats. The main areas of high quality habitats occur in central England as north–south trending belts, possibly facilitating dispersal along this axis. They are separated by low quality geo-habitats that may prevent east-west dispersal of fauna. In south-west England and Wales suitable geo-habitats occur as small isolated patches. Overall, this paper provides a new national-scale typology that is adaptable for studies in other geographic areas.     

齐齐哈尔市水土流失现状与趋势分析

齐齐哈尔市是黑龙江省水土流失重点治理区之一,也是全省风蚀最严重的地区,耕地水土流失面积占耕地面积的82.2%。分析了水蚀、风蚀的分布情况和草原"三化"状况,论述了水土流失变化趋势,水土流失严重,土壤肥力下降,治理速度落后于破坏速度。扎龙湿地中水利、交通、基础建设工程均占用了大面积湿地,由于干旱缺水造成了严重的水土流失。     

风蚀对中国北方脆弱生态系统碳循环的影响

风蚀是中国北方脆弱生态系统土壤质量退化和沙漠化的关键因素。文章基于土壤剖面普查和土壤侵蚀遥感调查数据,计算出风蚀土壤有机碳的侵蚀量和空间分布,并与风蚀区的净第一性生产力(NPP)比较。结果发现土壤风蚀区的一个显著特征是表层土壤有机质含量较小,并且随着土壤风蚀强度的增加,相应的表层土壤平均有机质含量和NPP基本上逐渐减小,而相应的土壤有机碳的侵蚀量却明显增大。在中国北方严重风蚀的脆弱生态区,土壤有机碳的侵蚀量超过了NPP,风蚀影响了生态系统的正常碳循环。     

Modeling Potential Shifts in Hawaiian Anchialine Pool Habitat and Introduced Fish Distribution due to Sea Level Rise

Global mean sea levels may rise between 0.75 and 1.9 m by 2100 changing the distribution and community structure of coastal ecosystems due to flooding, erosion, and saltwater intrusion. Although habitats will be inundated, ecosystems have the potential to shift inland, and endemic species may persist if conditions are favorable. Predictions of ecosystem migration due to sea level rise need to account for current stressors, which may reduce the resilience of these ecosystems. This study predicts the potential consequences of sea level rise on the groundwater-fed anchialine pool ecosystem in Hawaii. Scenarios of marine and groundwater inundation were compared with current patterns of habitat, introduced fishes, and land use. Results show that current habitats containing endemic anchialine shrimp will be increasingly inundated by marine waters. New habitats will emerge in areas that are low lying and undeveloped. Because of subsurface hydrologic connectivity, endemic shrimp are likely to populate these new habitats by moving through the coastal aquifer. In some areas, rising sea levels will provide surface connectivity between pools currently containing introduced fishes (tilapia, poeciliids) and up to 46 % of new or existing pools that do not contain these fish. Results predicting future habitat distribution and condition due to sea level rise will support conservation planning. Additionally, the interdisciplinary approach may provide guidance for efforts in other coastal aquatic ecosystems.     

沙漠公路风蚀破坏规律的数值模拟研究

通过Fluent软件对沙漠公路的风蚀破坏规律进行数值模拟研究。分析公路不同横断面时风沙流扰动、增速、减速、恢复的过程,确定路基(堑)高度、边坡坡率和路面宽度等公路断面设计参数对风沙流扰动的影响,提出沙漠公路路基(堑)风蚀破坏规律。结果表明：路面宽度的改变对路基沿程风速变化影响较小,各特征点处风速变化小于5%。路基(堑)高度和边坡坡率对风沙流扰动的影响较大。随路基(堑)高度增加,风沙流流场的扰动被增强,路基(堑)风蚀破坏越显著,当边坡坡率为1:1时,路基模型高度250 mm时的迎风路肩风速为模型高度60 mm时的 1.15倍,其背风坡脚风速降低45%;路堑模型高度250 mm时的背风堑顶风速为模型高度60 mm时的1.05倍,迎风堑脚处风速降低高达80%。建议沙漠公路宜采用中低路基(堑),不宜高填深挖。当路基(堑)高度一定,边坡坡率为1:1.75或1:2时,路基(堑)沿程风速变化平缓,沙漠路肩不易被吹蚀破坏;路堑中堑脚位置处不易出现堆积。其结论与室内风蚀风洞试验结果有很好的一致性     

Progress in the Research on the Impact of Wind Farms on Climate and Environment

Wind power has become one of the fastest growing renewable energy. With the large-scale deployment of wind farms in the world, people have started to pay attention to the impact of wind farms on the ecological environment and climate. This paper summarized the impact of wind farms on climate and ecological environment by investigating relevant literature: In the areas of wind farms, on the one hand, the set-up of wind turbines changes original aerodynamic roughness height and strengthens the dragging of the land surface against turbulence, directly affecting the turbulent motion of the boundary layer, resulting in the changes of intensity and pattern of material energy and water vapor exchange between land surface and near-surface atmosphere, further affecting the atmospheric circulation and climate. On the other hand, wind turbines convert the majority of the wind kinetic energy into electric energy, which produces the wake effect of the wind turbine. The budget patterns and spatial and temporal distribution of large-scale kinetic energy in the boundary layer are changed correspondingly, generating changes in various fluxes (heat flux, water vapor flux, etc.) in the atmosphere, which affect temperature, precipitation, and wind speed. Generally, the warming or cooling effect of wind farms on the near-surface is related to the stability of atmosphere. However, simulations in the global climate model showed that the average impact of wind farms on global climate is small, much smaller than the expected changes in greenhouse gas emissions and the interannual changes in natural climate.Wind power emits almost no carbon dioxide and pollutants. Compared with other traditional energy sources, it reduces water consumption but may generate some negative ecological impacts such as animal habitats, bird collisions, and noise, vision impact. However, some measures can be taken to mitigate these adverse effects.     

Wind erosion occurrence probabilities maps in the watershed of the Ningxia–Inner Mongolia reach of the Yellow River,China

The watershed of the Ningxia–Inner Mongolia reach of the Yellow River suffers serious wind erosion hazards and the areas with high wind erosion probabilities need to be identified to help in the building of the correct wind-sand blown hazard protection systems. In this study, the Integrated Wind-Erosion Modelling System model and Normalized Difference Vegetation Index (NDVI) data set were used to identify the distributions of threshold wind speeds and wind erosion occurrence probabilities. Through field observations, the relationships among NDVI, vegetation cover, frontal area (lateral cover), roughness length, and threshold friction velocity were obtained. Then, using these relationships, the spatial distributions of threshold wind speeds for wind erosion at a height of 10 m for the different months were mapped. The results show that the threshold wind speed ranged from 7.91 to 35.7 m/s. Based on the threshold wind speed distributions, the wind erosion occurrence probabilities of different months were calculated according to the current wind speed. The results show that the distributions of wind erosion occurrence probabilities and threshold wind speeds were related to each other. The resulting maps of threshold wind speeds and wind erosion occurrence probabilities would help environmental and agricultural researchers in determining some strategies for mitigating or adapting from wind erosion hazards.     

Study of Sand Dunes and Their Effect on Desertification of Cultivated Lands in Shaanxi Province, China Using Remote Sensing Techniques

About half of the arid and semi-arid lands in the world are deserts that comprise various types of aeolian sand dunes deposits. In Shaanxi Province, aeolian sand dunes cover considerable areas of the Yulin desert and northern Jinbian. Sand dunes are moving in the main wind direction and converting some agricultural area to wasteland. Remote sensing of sand dunes helps in the understanding of aeolian process and desertification. Remote sensing data combined with field studies are valuable in studying sand dunes, regional aeolian depositional history. In particular, active and inactive sand dunes of the north Shaanxi Province were studied using remote sensing and geographic information system. In this study, we describe the Landsat thematic mapper (TM) images, covering north Shaanxi Province, which were used to study the distribution, shape, size, trends, density and movement of sand dunes and their effect on desertification of cultivated lands. Estimation was made depending on soil erodibility factor (Ⅰ) and local climatic factor (C) during the period (June to September). The result indicates that soil erosion caused sand drift of 8.957 5, 7.03 ton for Yulin and Jinbian, respectively. The mean sand dunes movement rate were 4.37, 3.11 m, whereas, monthly sand dune advance rate were 1.092 5, 0.777 5 m, for the two locations, respectively. The study reveals that cultivated lands extended obliquely to the direction of sand dune movement are extremely affected, while other segments that extend parallel to the direction of the movement are not affected. Accordingly the north Shaanxi Province was divided into areas of different classes of potential risk. Moreover, blown sands and sand movement from neighboring highlands also affect the area of western desert.