呼伦贝尔地区土地荒漠化动态变化

呼伦贝尔地区是中国重要的天然草原和畜牧基地, 随着该地区经济和社会的发展及人类对资源的不合理利用, 土地荒漠化现象加重。笔者应用RS和GIS技术, 以1970 年MSS、2000 年ETM和 2007年CBERS数据为数据源, 主要采用人工目视解译方法, 并辅助野外调查验证, 获得三期解译数据, 并利用空间分析、网格剖分方法, 对呼伦贝尔地区荒漠化的时空变化情况进行研究。结果表明: 近40年来, 该地区土地荒漠化总面积不断增加, 1970 年该地区土地荒漠化面积为7408.76 km2 , 2000年为7 539.52 km2 , 2007年增加到7 852.12 km2 , 共增加面积443.36 km2。1970-2000年间, 沙漠化减轻、盐碱化加重的面积为134.09 km2 , 沙漠化加重、盐碱化减轻的面积为53.35 km2 ; 2000- 2007年间, 沙漠化减轻、盐碱化加重的面积为41.71 km2 , 沙漠化加重、盐碱化减轻的面积为172.8 km2。     

Landscape change and sandy desertification in arid areas: a case study in the Zhangye Region of Gansu Province, China

The Zhangye Region of Gansu Province is an important agricultural base in arid northwestern China. During the twentieth century, especially in the last five decades, the region has experienced sandy desertification. To document the status and causes of this deterioration, satellite images, meteorological and socioeconomic data to assess landscape change from 1993 to 2002 were interpreted and analyzed. The results show that during the intervening 9-year period the area of sandy lands has increased by 642.2 km², which consist of aeolian sand dune (357.1 km²) and potential sandy land (216.3 km²). Although the development and reversion of sandy desertification co-exist, the sandy desertification in this area seems serious and is attributable to the irrational use of water and land.     

Wadi Bakht revisited: Holocene climate change and prehistoric occupation in the Gilf Kebir region of the Eastern Sahara,SW Egypt

Geoarchaeological and chronological evidence from the remote Gilf Kebir Plateau in southwest Egypt suggests a new model for the influence of early and mid‐Holocene precipitation regimes on land‐use strategies of prehistoric settlers in what is now the center of the largest hyperarid area on earth. We hypothesize that the quantitatively higher, daytime, monsoon summer rainfall characteristic of the early Holocene (9300–5400 ¹⁴C yr B.P./8400–4300 yr B.C.) resulted in less grass growth on the plateau compared to the winter rains that presumably fell in the cool nights during the terminal phase of the Holocene pluvial (5400–4500 yr B.P./4300–3300 yr B.C.). The unparalleled climatic transition at 5400 yr B.P. (4300 yr B.C.) caused a fundamental environmental change that resulted in different patterns of human behavior, economy, and land use in the canyon‐like valleys and on the plains surrounding the plateau. The model emphasizes the crucial impact of seasonal rainfall distribution on cultural landscapes in arid regions and the lower significance of annual precipitation rates, with implications for future numeric climate models. It also serves as an example of how past climate changes have affected human societies. © 2004 Wiley Periodicals, Inc.     

Re-evaluating the impacts of human activity and environmental change on desertification in the Minqin Oasis, China

The Minqin Oasis and its adjacent regions in northern China experienced significant desertification beginning 2,000 years ago and continuing to the present, and numerous studies have claimed that human activities, especially the flourishing of agriculture, have played a major role in environmental change in this region. Our analysis suggests that the observed desertification was mainly controlled by changes in the water component of the ecosystem and the arid climate. The impacts of cultivation on desertification from 2,000 years ago to the mid-1900s appear to have been relatively minor compared to the impacts of the area’s arid climate and its native geomorphological processes. Although human activity has increased from the late-1940s to the present, and the areas of the oasis reclaimed for agriculture have reached a maximum, desertification over the past 50 years appears to be a continuing process that began thousands of years ago, and is mainly controlled by decreasing water levels caused by the arid climate, local geomorphological processes and overuse of water in the upstream. Although both human activities and climate variation are important drivers of the desertification process, and it is not possible to completely separate the human influence from the climate impact, key factors on controlling desertification should be investigated before we place the blame solely on the flourishing of agriculture in this region.     

The co-production of livelihoods and land use change: Case studies from South Africa and Ghana

Land use change and livelihood systems are often analyzed separately or with one “driving” the other. This “driver-feedback” relationship has been buttressed by approaches to social process that are often far too static. Actors are confronted with a bundle of choices that they must negotiate as they create pathways of change. These choices are always bound up in relations of power and the knowledges that are the conditions for and results of these relations. We suggest that land uses and livelihood are different manifestations of the social processes by which individuals and groups negotiate the everyday conditions that shape their lives. We propose a framework that extends current understandings of the relationship between land use change and livelihoods by treating social relations of power as the entry point into this complex relationship. We underpin our arguments with empirical examples from South Africa and Ghana that locate power/knowledge relations in the context of social change in both study areas.     

Potentiality of land and water resources in African Sahara: a case study of south Egypt

The investigated area is located south Egypt, between latitudes 22°00′N and 24°15′N, and longitudes 28°00′E and 30°00′E. It covers a total area of about 95,000.17 km². The area was remotely sensed to identify landscape and its land and water resources. A reconnaissance survey followed by detailed one was done to verify the information resulted from satellite images. The prevailing deposits of the area could be expressed as (1) the Nubian sandstone, (2) the Quaternary sediments, and (3) the sand dunes belt. Fourteen main and sub-main landforms were recognized, i.e., sand sheets (high, moderately high, moderate, and low), depressions (high, moderately high, moderate, and low), dry valleys, peniplains, footslopes, barchans, tablelands, and scattered hills. Associated soils were distinguished and classified as Typic Torripsamments, Typic Haplocalcids, Typic Torrifluvents, and Typic Haplodurids. Spatial variability of soil and water characteristics was identified through using ordinary Kriging interpolation method. Land surface temperatures in both summer and winter seasons were derived from thermal band, and soil temperature regimes were defined digitally as hyperthermic. Water potentiality was identified and classified according to salinity and sodicity hazards to C2-S1 and C3-S1. Using GIS techniques, soil potentiality spatial model (SPSM) was designed to get potentiality classes, i.e., high, moderately high, moderate, low, and very low.     

Monitoring desertification by remote sensing using the Tasselled Cap transform for long-term change detection

Sensitive areas like oases are threatened by climatic variations and human activities that can catalyze desertification processes. Remote sensing the Earth surface from satellites is a good tool to monitor such types of change through several techniques. In this paper a remote sensing method that has been widely used for vegetated areas is adapted to study dry regions. The method consists of a combination of the Change Vector Analysis and the Tasselled Cap (TC) transform. To adapt it to dryland conditions a new set of parameters for the TC transform is hereby calculated for the Landsat 8 OLI system. The new TC parameters are tested in the analysis of the surface change in Azraq Oasis, Jordan, over a time span of 30 years (1984–2013) for Landsat satellites images. Azraq is considered a good testing site since in the early 1990s it has been subject to a complete drying up of the superficial springs, mainly due to over-exploitation of the groundwater basin. Results show that the chosen technique is able to detect the expected change on the surface, consistent with photo-interpretation and historical information available.     

Unusually abundant refractory inclusions from Sahara 97159 (EH3): a comparative study with other groups of chondrites

Sixty-eight refractory inclusions and fragments were found in two polished thin sections of the Sahara 97159 EH3 chondrite, indicative of the highest abundance of refractory inclusions (22/cm², or 0.06 vol.%) in enstatite chondrites studied to date. All of the inclusions are intensely altered, mainly producing feldspathoids and albite, CaO depletion and minor Ti-rich compounds, such as Ti-sulfides. The alteration assemblages and FeO-poor spinel suggest that the reactions took place under reducing and SiO₂-rich conditions. This is consistent with the redox state of the host enstatite chondrite. The presence of Ti sulfides and low FeO alteration phases distinguishes alteration of E chondrite refractory inclusions from that of carbonaceous and ordinary chondrites.Most of the inclusions are referred to as Type A-like (35) and spinel-rich (26), respectively. Assuming melilite has been altered, these inclusions could be analogues of individual concentrically zoned objects of fluffy melilite-spinel-rich (Type A) and spinel-pyroxene-rich inclusions from carbonaceous chondrites such as the Ningqiang (CV anomalous) and Y 81020 (CO3) chondrites. Two inclusions consist mainly of Ca-pyroxene, fine-grained alteration products (feldspathoids and albite) and spinel. They are probably altered fragments of Ca-pyroxene-plagioclase-rich (Type C) inclusions, assuming all plagioclase has been altered to produce the fine-grained groundmass. Five other inclusions are hibonite and/or corundum bearing, similar to those reported in carbonaceous chondrites. Abundance ratios of various types of the inclusions from Sahara 97159 are similar to those from Ningqiang and Y 81020.Most of the observations, including mineral assemblages, mineral chemistry, texture, bulk compositions, O isotopic compositions and REE patterns, of the Sahara inclusions suggest a common reservoir of refractory inclusions in enstatite, ordinary and carbonaceous chondrites. The apparent differences, such as absence of melilite and anorthite, rare Wark-Lovering rim and small size, can be explained by intense alteration due to large change of postformation environment of these inclusions, size sorting and collision during transfer. Hence, these differences are not inconsistent with the common reservoir model. Refractory inclusions in non-carbonaceous chondrites may put additional constraints on origins of refractory inclusions, and provide hints for a spatial relationship of their host meteorites.     

Chad Basin: Paleoenvironments of the Sahara since the Late Miocene

Since the mid 1990s, the Mission paléoanthropologique francotchadienne (MPFT) conducts yearly paleontological field investigations of the Miocene-Pliocene of the Chad Basin. This article synthesizes some of the results of the MPFT, with focus on the Chad Basin development during the Neogene. We propose an overview of the depositional paleoenvironments of this part of Africa at different scales of time and space, based on a multidisciplinary approach (sedimentary geology, geomorphology, geophysic, numerical simulations and geochronology). The Miocene-Pliocene paleoenvironments are examined through the sedimentary archives of the early hominids levels and the Holocene Lake Mega-Chad episode illustrates the last major paleoenvironmental change in this area. The sedimentary record of the Chad Basin since the Late Miocene can be schematized as the result of recurrent interactions from lake to desert environments.     

Carbonate metasomatism in the lithospheric mantle: peridotitic xenoliths from a melilititic district of the Sahara basin

The petrological and geochemical study of harzburgitic and dunitic xenoliths from the melilititic district of In Teria (Algerian Sahara) shows that the lighospheric mantle of this region has been affected by a multi-stage metasomatism. The first metasomatic event is related to the injection of alkali silicated (basaltic or kimberlitic) melt and was responsible for the crystallization of phlogopite at depths ranging between 80 and 100 km and the crystallization of amphibole at about 60 km. During this first event, carbonate probably precipitated in the garnet stability field. In a second stage, the spinal peridotites suffered strong mineral changes resulting in an extensive formation of high-Cr endiopside and leading to conversion of harzburgite and dunite into lherzolite and wehrlite. These changes are associated with an enrichment in the most incompatible trace elements including light REE (rare-earth elements), Ta, Th and variable values of ratios such as Th/La and Ta/La. This second event is atributed to the injection (under conditions of decarbonatation and release of CO₂) of a carbonatitic melt resulting from incipient melting of the garnet peridotites, which were previously carbonated. This interpretation is corroborated by the calculation of a diffusion-percolation model which reproduces well the observed distribution of incompatible trace elements in the spinel peridotites. Given the proposed sequence of events, it appears that most of the specificities of the In Teria xenoliths can be explained by the successive geochemical modifications induced within the lithospheric mantle during reheating.     

贵州贞丰-关岭花江喀斯特石漠化过程中岩土体化学元素含量与石漠化差异性关系研究

不同等级石漠化地区岩体和土体中化学元素有较大的差异,表现在石漠化演化过程中不断被改变,化学元素的差异性对石漠化等级差异性的形成有着内在的关联性。文章以贵州贞丰-关岭花江石漠化治理示范区为研究区,选取11处样地的岩石样和土样,对其进行室内实验分析,以了解该地区岩石和土壤的化学元素含量,从而研究其含量的差异性与石漠化等级之间的关系。结果显示:① 岩体中CaO/ MgO的值越大,Rb/Sr值越低,石漠化等级越高。②在碳酸盐母岩逐渐溶蚀和风化成土的过程中,岩体中Ca、Mg离子被带走,导致成土后土体中Ca、Mg离子含量降低,但强度石漠化地区的土体中Mg离子含量却增加。③不同等级石漠化地区的样品化学元素流失和富集的程度略有差异,一般强度和潜在石漠化地区(离子)含量要高于轻度和中度石漠化地区。④土体中Rb/Sr值越大,石漠化等级越强。该研究可以为示范区的水土流失及石漠化治理提供理论和实践依据。      

Women and desertification: The question of responsibility

Campaigns against desertification frequently address women, who are held responsible for rapid population growth and biomass burning. It is shown here how desertification is caused by the erosion of social coherence. This diagnosis requires a fundamental change in anti-desertification policies.     

基于Landsat-X GEVI的贵州纳雍地区2003-2015年岩溶石漠化分布变化遥感调查

岩溶石漠化是困扰中国西南岩溶地区发展的一种脆弱的生态环境,为了解贵州纳雍地区岩溶石漠化的改善情况,基于Landsat数据利用改进增强型植被指数模型（GEVI）方法提取了2003年和2015年的岩溶石漠化信息,分别为540.06 km2和390.99 km2,并将两期岩溶石漠化信息进行叠加分析和对比研究,发现该地区岩溶石漠化面积减少了149.07 km2,改善率（减少率）达12.88%,尤其是原成片分布的石漠化区域（如朝阳谷、滥坝和猫场等地）多呈碎斑状缩小,且发现研究区岩溶石漠化位置有自南西向北东迁移的现象,迁移面积为289.47 km2,以中度岩溶石漠化为主,说明治理与破坏同步,防治形势仍很严峻,但岩溶石漠化总面积减少,生态状况呈良性发展态势,反映出近年来综合治理成效显著。      

Paleorivers and geoarchaeology in the southern Egyptian Sahara

Interpretation of Shuttle Imaging Radar (SIR) images acquired during the November 1981 flight of Columbia led to the idea that a paleodrainage system of regional and perhaps transcontinental proportions crossed southern Egypt and northern Sudan prior to the onset of Quaternary aridity. Three seasons of field investigations in two locales (Wadi Arid and Wadi Safsaf, some 70-80 km apart) near the Sudan border of southern Egypt confirmed initial interpretations of the radar images and produced geologic evidence of fluvial deposition in broad “radar river” valleys (designated RR-1) whose presence is now obscured by eolian sand sheets. Development of an integrated, regional river system probably occurred in the late Paleogene or early Neogene. the river courses eventually were disrupted by tectonism, volcanism, and stream piracy. Their broad valleys were almost fully aggraded long before the middle Pleistocene appearance of man in the area. Some of the large paleovalleys on the radar images contain narrow (0.05-2.0 km wide), braided inset channels (designated RR-2). the RR-2 channels, we believe, represent the last episodes of running water in the valleys during the Quaternary pluvials. In Wadi Arid (the type area for the RR-1 valleys) 36 backhoe trenches and manual excavations yielded Acheulian handaxes, flakes, and cores from nearshore alluvial sediments and surface and shallow subsurface locales. These assemblages are typologically Middle to Late Acheulian and date from ca. 0.15th 0.5 million years ago. the unabraded, unrolled, buried artifacts and their geological contexts indicate that human groups were widely present in a subhumid riparian environment along the edges of the ancient valleys, while these localities were undergoing episodic, local aggradation. Scarce Middle Paleolithic and abundant Neolithic assemblages are widespread along the edges of Wadi Arid and bordering interfluves. In Wadi Safsaf, another broad RR-1 valley, geologic evidence from 20 backhoe excavations demonstrates that an RR-2 channel complex is inset into the alluvial fill in the central part of the valley. No artifacts were found in the alluvium excavated there, but Late Acheulian, Middle Paleolithic, and Neolithic surface assemblages are present nearby. Stratigraphic relations indicate the RR-2 channels are late Pleistocene in age; they were already fully aggraded and their surfaces deflated before an eolian sand sheet of Holocene age was deposited on them. Bir Safsaf, on the northern edge of Wadi Safsaf, was a magnet for Late Acheulian populations, and the paleovalley just south of the bir is bordered with extensive alignments of artifacts, mainly handaxes. Some of these handaxes were found in situ, embedded in alluvial sediments, while others appear to have been exposed on the surface by deflation of the valley fill. The accumulated data support a provisional archaeo-geochronological framework for the last half-million years in the Wadi Arid-Wadi Safsaf area. This framework provides a new geomorphic explanation for the widespread distribution of buried and exposed Middle Acheulian and Late Acheulian assemblages. the interpretation emphasizes the importance of exploring the non-oasis zones for their archaeological and geochronological potential. Although our research has literally only scratched the surface, it demonstrates the potential of radar imaging for defining ancient drainage patterns in arid regions and their associated habitats for human occupation.     

典型喀斯特石漠化地区植被动态监测与土地利用变化的影响分析

基于2001至2014年MOD13Q1数据集、数字地面高程数据以及中梁山地区多期土地覆盖数据,进行植被覆盖度（FVC）估算及其变化趋势模拟、多期土地利用转移矩阵分析,探讨中梁山地区植被覆盖度动态变化特征、土地利用的时空变化特征以及土地利用和地形同植被覆盖度间的响应机制。研究结果表明：中梁山76.69%的区域为植被改善区,退化区面积占总面积的10.12%,存在明显的改善趋势,生态情况得到良好恢复;人类活动对中梁山区域影响方式主要表现为耕地向林地和建设用地转化的特点;植被生长趋势的空间异质性与坡度有关,坡陡区植被改善面积约为退化面积的14倍,缓坡区仅为7倍;植被退化现象受人览活动的影响较大,而人类晃动对植被改善影响较小,植被改善主要与植物的自然生长演替有关。     

Vulnerability and adaptive capacities to slope failure threat: a study of the Klang Valley Region

This article examines the relationship between vulnerability and adaptive capacities of urban dwellers to slope failure threats. The Klang Valley Region in Peninsular Malaysia was selected as the study area based on the increasing frequency and impact of slope failures in the last decade. The study identified, examined, and mapped 10 slope failure locations, and the vulnerability characteristics of urban dwellers staying in areas that are prone to and threatened by slope failures were described. The identified vulnerability indicators are related to factors such as (1) socio-economic status, (2) population, (3) external characteristics, (4) physical structure of dwellings, and (5) adaptation measures. Finally, the perceptions of the residents who are at risk of slope failure hazards and their inherent coping mechanisms were analyzed. A model describing the relationships among slope failure threats, vulnerability of urban dwellers, and their adaptive capacities was formulated.     

A mineralogical and geochemical study of polymict eucrite discovered in Sahara of southwest Algeria

NWA2268 is a polymict eucrite discovered in the Sahara, at southwest Algeria, close to the region of Tindouf. This meteorite weighs 65 g and presents a thin black fusion crust. The rock is fine- to medium-grained breccia and contains mineral fragments of plagioclases, pyroxenes, spinel, olivine and silica. The rock contains some basaltic fragments with sub-ophitic or cumulative textures, constituted by plagioclases and exsolved pigeonite. Pyroxferroite grains are present and locally destabilised in an association of hedenbergite, fayalite and silica. It also presents unequilibrated eucritic clast with heterogeneous pyroxenes and plagioclases compositions. Pyroxenes in the all of the other clasts have equilibrated composition, with exolved pigeonites with augite lamellaes. This polymict eucrite contains also partially devitrified glass that represents impact melts linked to impact event. None recrystallization of this glass confirms a lack of post-brecciation metamorphism. Diogenitic fragments are less abundant than 10 %. The oxygen isotopic composition of NWA2268 is Δ¹⁷O (?0.43). This meteorite is interpreted as belonging to the HED group attributed to the 4-Vesta asteroid.     

Geological exploration history of the Eastern Sahara

The major contributions to our knowledge of the geological history of the East Saharan countries are described. Much work has been published on the history and progress of geographical, socioeconomic and archaeological exploration in North Africa. Little attention, however, has been paid to the question of how our knowledge of the geology of this vast area was developed. Thus, even though progress in geology is vital to the development of Saharan countries, little has been recorded of this progress. Without an understanding of regional geology and without a good knowledge of groundwater, mineral and petroleum potentials, these countries would be in very different situations today. The author has, over the last 35 years, been involved in scientific research and exploration of petroleum, mineral and groundwater resources in Libya, Egypt, Sudan and Chad.     

喀斯特石漠化演变轨迹的典型案例研究——以贵州盘县为例

本文以1974年MSS、1999年TM、2007年TM影像为基本数据源,辅以实地踏勘,考虑一个完整的峰丛洼地等,扣除其平坝部分后作为评价单元,获得了贵州省盘县3个时期的石漠化数据并计算了石漠化和无石漠化土地的演变轨迹。相应于1974年、1999年、2007年3个时段,研究区土地退化演变轨迹可分为8种,并可进一步归纳为不变型、逆转减弱型、反复型和加重型4种演变过程类型,从1974年、1999年到2007年未发生过变化的不变型轨迹面积占较高的比例。研究区的喀斯特土地可分为石漠化土地、无石漠化土地、石漠化已恢复土地和潜在可恢复石漠化土地。     

Fuelwood and desertification: Sahel orthodoxies discussed on the basis of field data from the Gourma region in Mali

Until recently orthodoxies on fuelwood and desertification have formed the cornerstones of mainstream views in research and development related to natural resources in the Sahel. Based on an empirical study of the fuelwood situation in the Gourma region in Mali, this article throws a critical light on these viewpoints. There is no relationship between deforestation and domestic fuelwood consumption in the Gourma. The fuelwood used comes from dry wood collected from dead trees. Collection distances are, however, getting longer; so people need to use more time for the collection of wood, or more of their limited incomes have to be spent on buying fuelwood. Therefore, the fuelwood problem in the Gourma is of a social and economic rather than an ecological character. Sahel orthodoxies, which are manifested in the national Malian plan to fight desertification, are used by the Water and Forests Service to justify their policy of harassment towards the rural poor. These orthodox beliefs about environmental issues in drylands are generalizations which tend to gloss over important regional diversities. The data presented should therefore not be used to create new orthodoxies. They should rather be regarded as a warning not to use generalizations on local realities about which there is no reliable information.