Dynamics of aeolian desertification and its driving forces in the Horqin Sandy Land,Northern China

Aeolian desertification is one of the most serious environmental and socioeconomic problems in arid, semi-arid, and dry subhumid zones. Understanding desertification processes and causes is important to provide reasonable and effective control measures for preventing desertification. With satellite remote sensing images as data source to assess the temporal and spatial dynamics of desertification from 1975 to 2010 in the Horqin Sandy Land, dynamic changes of aeolian desertification were detected using the human–machine interactive interpretation method. The driving factors of local desertification were analyzed based on natural and socioeconomic data. The results show that aeolian desertified land in the study area covered 30,199 km² in 2010, accounting for 24.1 % of the study area. The total area of aeolian desertified land obviously expanded from 30,884 km² in 1975 to 32,071 km² in 1990, and gradually decreased to 30,199 km² in 2010; aeolian desertified land represented an increasing trend firstly and then decreased. During the past 35 years, the gravity centers of desertified lands that are classified as extremely severe and severe generally migrated to the northeast, whereas those that are moderate and slight migrated to the northwest. The migration distance of severely desertified land was the largest, which indicated the southern desertified lands were improved during the last few decades. In addition, the climatic variation in the past 35 years has been favorable to desertification in the Horqin Sandy Land. Aeolian desertified land rapidly expanded from 1975 to 1990 under the combined effects of climate changes and unreasonable human activities. After the 1990s, the main driving factors responsible for the decrease in desertification were positive human activities, such as the series of antidesertification and ecological restoration projects.     

济南市空气中颗粒物来源与防治对策

颗粒物(总悬浮颗粒物TSP及可吸入颗粒物PM10)已成为济南市空气污染的首要污染物,其主要来源为扬尘、煤烟尘和风沙尘.三类尘对TSP和PM10的贡献分别为扬尘:34%和30%、煤烟尘:25%和19%、风沙尘:18%和22%.文中在阐明颗粒物源解析的分析方法及结果基础上,提出了颗粒物污染的防治对策.     

Changes in wind erosion over a 25-year restoration chronosequence on the south edge of the Tengger Desert,China: implications for preventing desertification

Wind erosion is a primary cause of desertification as well as being a serious ecological problem in arid and semi-arid areas across the world. To determine mechanisms for restoring desertified lands, an unrestored shifting sand dune and three formerly shifting sand dunes (desertified lands) that had been enclosed and afforested for 5, 15, and 25 years were selected for evaluation on the south edge of the Tengger Desert, China. Based on sampling heights between 0.2 and 3 m, the critical threshold average wind speed was 6.5 m s^?1 at 2 m where the sand transport rate was reduced from 285.9 kg m^?2 h^?1 on the unrestored dunes to 9.1 and 1.8 kg m^?2 h^?1 on the sites afforested and enclosed for 5 and 15 years, respectively. The percentage of wind eroded area was reduced from 99.9% on the unrestored dune to 94.5, 9.0, and 0.5% on the sites afforested and enclosed for 5, 15, and 25 years, respectively. Wind erosion was effectively reduced after 15 years. Although there were different driving factors for wind erosion mitigation on the different restoration stages, an increase in the vegetation cover, surface roughness, soil shear strength, soil clay content, organic matter, and reduction in the near-surface wind speed were the primary variables associated with the restoration chronosequence. We conclude that reducing the wind speed and developing a biological crust through vegetation restoration were the critical components for restoration of desertified land.     

Impact of Sand Dune Stabilization Structures on Soil and Yield of Millet in the Semi-Arid Region of NW Nigeria

The low-rainfall ecologies of the northern fringes of Nigeria are prone to desertification and sand dune activities that are phenomenal and extensive. Stabilization structures put in place by various governmental and non-governmental agencies to check desertification in northwestern Nigeria were evaluated with respect to efficiency, impact on soil development and yield of millet. The study focused on the active and stabilized sand dune formations in NW Nigeria. Various stabilization techniques were identified within Gidan Kaura (the study site) and results were compared with an unstabilized sand dune (control site). Results obtained indicated that the sand dunes within the study area are still active despite the numerous stabilization structures, some of which were established over 15 years ago. Shelterbelts were the most effective techniques in sand dune stabilization and soil development when properly sited across wind direction. Shelterbelts recorded significantly higher levels of pH, organic carbon, total nitrogen, exchangeable bases and micronutrients except for copper, when compared with all other treatments. The least effective of all the structures was mechanical fencing, probably due to the inadequate quantity of plant residues used in its construction. The impact of the various structures on the physical and chemical soil properties was evaluated for surface soils as were the structures on the yield of millet in stabilized dunes and non-dune areas. The results are discussed in depth in this paper.     

Desertification in Russia: Problems and solutions (an example in the Republic of Kalmykia-Khalmg Tangch)

During the second half of the 20th century Kalmykia has undergone severe desertification. Under Soviet rule, rangelands were increasingly devoted to animal production, and pastures were converted to cropland in a campaign to increase crops. Pastures were grazed two to three times their sustainable production, saiga populations and habitat greatly decreased, more than 17 million ha were subjected to wind erosion, 380,000 ha were transformed into moving sands, and 106,000 ha were ruined by secondary salinization and waterlogging. By the 1990s almost 80% of the Republic had undergone desertification, and 13% had been transformed into a true desert. In 1986 the General Scheme of Desertification Control was formulated. The scheme called for rotating pastures, reclaiming blown sand using silviculture, tilling overgrazed pastures and sowing fodder plants, and developing water supplies for pastures. In its early years the scheme has been successful. But the management of restored pastures usually reverts to the same farms responsible for the poor conditions, and there is great apprehension that degradation could reoccur. This case study concludes that the general cattle and agriculture development in Kalmykia is unviable for ecological and economic reasons, that Kalmykia should implement an adaptive policy oriented toward conservation and accommodating the interrelation and variability of land resources, that the desertification problem can be solved only by changing agrarian policy as a whole, and that a desertification control program must become an integral part of economic and social development of the Republic.     

Community Based Interventions as a Strategy to Combat Desertification in the Arid and Semi-Arid Rangelands of Kajiado District, Kenya

Vegetation degradation, especially the disappearance of woody vegetation and a diminished grass cover, has aroused the concern of the Maasai community (semi-nomadic pastoralists) of Kajiado District, Kenya. The district is one of Kenya’s arid and semi-arid districts. Over recent years, they have observed their land resources deteriorate due to the desertification process caused by the land use practices of man. They have identified indicators of desertification such as increase of bare lands, which have been invaded by previously unknown grasses and weeds that are of no economic value, and also the disappearance of some useful plant species. It is due to the above concerns that a group of 30 farmers have been very keen to participate in on-farm research to strategize on ways to halt and even reverse the desertification process. The participatory research has identified useful trees that the farmers have been planting around homesteads, as woodlots on their farms to provide woodfuel, shade, and to act as windbreaks. They have also identified species for planting as live fences instead of using thorny tree branches as fencing material, which contributes further to the desertification process. Due to the termite menace on young tree seedlings, the farmers use indigenous knowledge to prepare concoctions using locally available materials, which they apply to planting holes and on seedlings. During awareness campaigns, the farmer research group highlights the need to conserve vegetation resources and also expounds on the concept of planting two trees after one is felled.     

玛纳斯河流域荒漠草地沙化遥感监测研究

以1989—2016年玛纳斯河流域TM/OLI遥感影像为数据源,利用混合像元分解技术,计算玛纳斯河流域草地总覆盖度和裸沙面积。在此基础上通过监测年与基期年的比较,计算草地覆盖度相对基期年的减少率和裸沙面积相对基期年的增加率两个监测指标,依据《天然草地退化、沙化、盐渍化的分级指标》(GB 19377—2003),对计算出的两个指标分别进行沙化等级评定和赋值,将两种评定结果相综合来监测草地沙化。结果表明,玛纳斯河流域近30年来荒漠草地沙漠化总体呈现先增加后降低的趋势。分析表明,玛纳斯河流域草地沙化是人为和自然因素双重作用的结果。     

Assessing the effects of dam building on land degradation in central Iran with Landsat LST and LULC time series

This study aimed to analyze the impact of Zayandehrood Dam on desertification using the spatio-temporal dynamics of land use/land cover (LULC) and land surface temperature (LST) in an arid environment in central Iran from 1987 to 2014. The LULC and LST images were calculated from Landsat TM, ETM+, and OLI data, and their accuracies were assessed against reference data using error matrix and linear regression analysis. Results showed that salty and bare lands increased up to 57,302 ha, while agricultural lands declined substantially (28,275.58 ha) in the region. The changes in LULC classes resulted in dramatic variations in LST values. The average temperature showed a 5.03 °C increase, and the minimum temperature increased by 5.66 °C. LST had an increasing trend in bare lands (8.74 °C), poor rangelands (6.8 °C), agricultural lands (9.46 °C), salty lands (9.6 °C), and residential areas (3.18 °C) in this 27-year period. Rainfall and temperature trend analysis revealed that the main cause of these extreme changes in LULC and LST was largely attributed to the drying up of Zayandehrood River due to dam construction and allocating water mainly for industrial sectors. Results indicate that in addition to LULC changes, the spatio-temporal variations of LST can be used as an effective index in desertification assessment and monitoring in arid environments.     

Application of wind-profiling radar data to the analysis of dust weather in the Taklimakan Desert

The Urumqi Institute of Desert Meteorology of the China Meteorological Administration carried out an atmospheric scientific experiment to detect dust weather using a wind-profiling radar in the hinterland of the Taklimakan Desert in April 2010. Based on the wind-profiling data obtained from this experiment, this paper seeks to (a) analyze the characteristics of the horizontal wind field and vertical velocity of a breaking dust weather in a desert hinterland; (b) calculate and give the radar echo intensity and vertical distribution of a dust storm, blowing sand, and floating dust weather; and (c) discuss the atmosphere dust counts/concentration derived from the wind-profiling radar data. Studies show that: (a) A wind-profiling radar is an upper-air atmospheric remote sensing system that effectively detects and monitors dust. It captures the beginning and ending of a dust weather process as well as monitors the sand and dust being transported in the air in terms of height, thickness, and vertical intensity. (b) The echo intensity of a blowing sand and dust storm weather episode in Taklimakan is about ?1~10 dBZ while that of floating dust ?1~?15 dBZ, indicating that the dust echo intensity is significantly weaker than that of precipitation but stronger than that of clear air. (c) The vertical shear of horizontal wind and the maintenance of low-level east wind are usually dynamic factors causing a dust weather process in Taklimakan. The moment that the low-level horizontal wind field finds a shear over time, it often coincides with the onset of a sand blowing and dust storm weather process. (d) When a blowing sand or dust storm weather event occurs, the atmospheric vertical velocity tends to be of upward motion. This vertical upward movement of the atmosphere supported with a fast horizontal wind and a dry underlying surface carries dust particles from the ground up to the air to form blown sand or a dust storm.     

Desertification in Australia: An eye to grass roots and landscapes

Desertification in some form is estimated to have occurred over about 42% of the 5 million km² of arid and semiarid lands in Australia. The most common form of desertification is loss of perennial grasses from grasslands, savannas, and open woodlands, often with a replacement by inedible shrubs. Desertification continues to be a problem, especially during droughts when grazing pressures reduce ground cover, laying bare landscapes to wind and water erosion. But two national programs, Drought Alert and Landcare, are giving new hope in controlling land degradation. Both use a grassroots approach by promoting action through local pastoralist and farmer groups and by encouraging the use of effective techniques for rehabilitating landscapes. A strategic application of ponding banks and contour traps with an eye to the landscape has proven successful in stopping and reversing desertification processes.     

A holistic approach towards assessment of severity of land degradation along the Great Wall in northern Shaanxi Province,China

The farming and grazing interlocked transitional zone along theGreat Wall in northern Shaanxi Province is particularly vulnerable to desertification due to its fragile ecosystem and intensive human activity. Studies reveal that desertification isboth a natural and anthropogenic process. Four desertificationindicators (vegetative cover, proportion of drifting sand area, desertification rate, and population pressure) were used to assess the severity of desertification in a GIS. The first threefactors were derived from multitemporal remote sensing and landinventory data. The last factor was calculated from census data.It was found that the overall severity of land degradation in thestudy area has worsened during the last two decades with severely, highly and moderately degraded land accounting for 84.2% of the total area in 1998. While the area affected by desertification has increased, the rate of desertification has also accelerated from 0.74 to 0.87%. Risk of land degradation in the study area has increased, on an average, by 155% since 1985. Incorporation of both natural and anthropogenic factors inthe analysis provides realistic assessment of risk of desertification.     

石河子垦区农业生态环境

对垦区农业环境影响较突出的水污染状况，土壤次生盐渍化及土地沙化等环境问题进行研究分析，认为：垦区农业环境生态保护要兼顾垦区内外，绿洲内制约农业经济发展的重要问题仍然是水资源合理利用和土壤沙漠化问题，城市生态要严格控制工业废水的排放。     

Sandy desertification change and its driving forces in western Jilin Province, North China

This paper investigates the sandy desertification change between 1986 and 2000 in the western Jilin province, North China. Land use and land cover data were obtained from Landsat TM data by using a supervised classification approach. We summarized the total area of desertified land by each county, as well as the area for each of the four categories of desertified land. The changes of different types of land use and land cover between 1986 and 2000 were calculated and analyzed. Taking Tongyu and Qianan as examples, both human and natural driving forces of the sandy desertification were analyzed. Our analyses indicate that the material sources and windy, warm and dry climate are the immanent causes of potential land desertification, while the irrational human activities, such as deforestation, reclaiming and grazing in the grassland, are the external causes of potential land desertification. However, rational human activities, such as planting trees and restoring grassland can reverse the land desertification process. Furthermore, the countermeasures and suggestions for the sustainable development in ecotone between agriculture and animal husbandry in North China are put forward.     

Land desertification monitoring and assessment in Yulin of Northwest China using remote sensing and geographic information systems (GIS)

The objective of this study is to develop techniques for assessing and analysing land desertification in Yulin of Northwest China, as a typical monitoring region through the use of remotely sensed data and geographic information systems (GIS). The methodology included the use of Landsat TM data from 1987, 1996 and 2006, supplemented by aerial photos in 1960, topographic maps, field work and use of other existing data. From this, land cover, the Normalised Difference Vegetation Index (NDVI), farmland, woodland and grassland maps at 1:100,000 were prepared for land desertification monitoring in the area. In the study, all data was entered into a GIS using ILWIS software to perform land desertification monitoring. The results indicate that land desertification in the area has been developing rapidly during the past 40 years. Although land desertification has to some extent been controlled in the area by planting grasses and trees, the issue of land desertification is still serious. The study also demonstrates an example of why the integration of remote sensing with GIS is critical for the monitoring of environmental changes in arid and semi-arid regions, e.g. in land desertification monitoring in the Yulin pilot area. However, land desertification monitoring using remote sensing and GIS still needs to be continued and also refined for the purpose of long-term monitoring and the management of fragile ecosystems in the area.     

The relative role of climate change and human activities in the desertification process in Yulin region of northwest China

To overcome the shortcoming of existing studies, this paper put forward a statistical vegetation–climate relationship model with integrated temporal and spatial characteristics. Based on this model, we quantitatively discriminated on the grid scale the relative role of climate change and human activities in the desertification dynamics from 1986 to 2000 in Yulin region. Yulin region’s desertification development occurred mainly in the southern hilly and gully area and its reverse in the northwest sand and marsh area. This spatial pattern was especially evident and has never changed thoroughly. From the first time section (1986–1990) to the second (1991–1995), the desertification was developing as a whole, and either in the desertification development district or in the reverse district human activities’ role was always occupying an overwhelmingly dominant position (they were 98.7% and 101.4%, respectively), the role of climate change was extremely slight. From the second time section (1991–1995) to the third (1996–2000), the desertification process was reaching a state of stability, in the desertification development district the role of climate change was nearly equivalent to that of human activities (they were 46.2% and 53.8% separately), and yet in the desertification reverse district, the role of human activities came up to 119.0%, the role of climate change amounted to ?19.0%. In addition, the relative role of climate change and human activities possessed great spatial heterogeneity. The above conclusion rather coincides with the qualitative analysis in many literatures, which indicates that this method has certain rationality and can be utilized as a reference for the monitoring and studying of desertification in other areas.     

Measurement of gas diffusion through soils: comparison of laboratory methods

Gas movement through soils is important for ecosystems and engineering in many ways such as for microbial and plant respiration, passive methane oxidation in landfill covers and oxidation of mine residues. Diffusion is one of the most important gas movement processes and the determination of the diffusion coefficient is a crucial step in any study. Five laboratory methods used for measuring the relative gas diffusion coefficient (D(s)/D(o)) were compared using a loamy sand, a porous media commonly found in agricultural fields and in several engineered structures, such as in landfill final covers. In the absence of macropores, all methods gave rather similar values of D(s)/D(o). Methods allowing the study of microscale variability indicated that the presence of macropores highly influenced gas movement, thus the value of D(s)/D(o), which, near a macropore may be one order of magnitude higher than in regions without macropores. Repacked columns do not allow the study of heterogeneity in D(s)/D(o). Natural spatial variability in D(s)/D(o) due to water distribution and preferential pathways can only be studied in large systems, but these systems are difficult to handle. Advantages and disadvantages of each method are discussed.     

Surface disturbances: Their role in accelerating desertification

Maintaining soil stability and normal water and nutrient cycles in desert systems is critical to avoiding desertification. These particular ecosystem processes are threatened by trampling of livestock and people, and by off-road vehicle use. Soil compaction and disruption of cryptobiotic soil surfaces (composed of cyanobacteria, lichens, and mosses) can result in decreased water availability to vascular plants through decreased water infiltration and increased albedo with possible decreased precipitation. Surface disturbance may also cause accelerated soil loss through wind and water erosion and decreased diversity and abundance of soil biota. In addition, nutrient cycles can be altered through lowered nitrogen and carbon inputs and slowed decomposition of soil organic matter, resulting in lower nutrient levels in associated vascular plants. Some cold desert systems may be especially susceptible to these disruptions due to the paucity of surface-rooting vascular plants for soil stabilization, fewer nitrogen-fixing higher plants, and lower soil temperatures, which slow nutrient cycles. Desert soils may recover slowly from surface disturbances, resulting in increased vulnerability to desertification. Recovery from compaction and decreased soil stability is estimated to take several hundred years. Re-establishment rates for soil bacterial and fungal populations are not known. The nitrogen fixation capability of soil requires at least 50 years to recover. Recovery of crusts can be hampered by large amounts of moving sediment, and re-establishment can be extremely difficult in some areas. Given the sensitivity of these resources and slow recovery times, desertification threatens million of hectares of semiarid lands in the United States.     

北方沙尘暴对杭州大气环境的影响及应对措施

简述了我国沙尘天气的形成与分级情况。分析了我国沙尘天气的发展趋势与原因及其对杭州大气环境的影响情况。指出我国沙尘天气的发展有越演越烈的趋势 ,对杭州大气环境的影响时间延长 ,频次增加 ,危害程度加重 ,范围扩大。对防治沙尘天气污染大气环境提出了应对措施。     

Native Seed Collection and Use in Arid Land Reclamation: A Low-Tech Approach

Loss of vegetation production in arid lands has been difficult to remediate and has signifi- cant economic impacts on human populations. Restoration efforts based on non-local materials and large-scale mechanization have not been capable of efficiently reversing the trend of environmental degradation. The use of traditional knowledge and simplified methods of seed harvesting, storing, marketing and soil preparation have proven that regeneration of native species and efficient land reclamation is possible in areas that have traditionally been considered degraded beyond redemption. This paper describes a method of land reclamation that combines tradition and simple mechanics that can be applied in all arid areas that face desertification. Because the work builds on cultural practices long used in non-industrialized societies, it is particularly adapted to rural areas. The methods described have the potential to open new low-tech economic opportunities to all segments of local non-urban populations while combating desertification and creating a more ecologically sound environment.     

甘家湖湿地边缘带土地荒漠化演变中土壤颗粒分形特征

采用分形理论,研究了甘家湖湿地边缘带不同景观变化类型土壤颗粒体积分形维数的特征。结果表明,（1）从芦苇湿地边缘、胡杨林土、梭梭灌木林土、芦苇湿地、耕地周边、耕地到盐化草甸土的土壤粒径变化可以看出：湿地边缘带土壤荒漠化演变中砂粒含量在逐渐上升,粉粒、粘粒含量逐渐下降。这表明湿地边缘带人为的放牧、开垦、牛羊践踏对土壤产生了...