中国北方沙漠化的若干问题

随着经济、社会的发展,沙漠化问题对自然环境和社会发展的影响愈来愈深刻,已得到国际社会的普遍重视,作为沙漠化问题极其严重的国家,我国在对沙漠化的认识及治理上,经过多年工作取得了一些成就.本文根据已有的经验和研究成果,就中国北方沙漠化的成因、发展过程、灾害评价及防治机理等方面做一简单探讨,以便为今后更好地开展沙漠化研究工作起一定的参考作用.     

Quaternary deposits in the Maltese Islands: a microcosm of environmental change in Mediterranean lands

The Quaternary deposits of the Mediterranean countries provide clear evidence of past environments, and of environmental change. Modern work enables the reinterpretation of these deposits and shows arid glacial stages and humid interglacial stages, with the Holocene characterised by considerable human impact, mostly resulting from agricultural activity. In this paper, examples of typical Mediterranean Quaternary lithofacies, including tufa and slope, fluvial, coastal, aeolian and cave deposits are described from the Maltese Islands. The deposits are correlated and their climatic signal is interpreted to provide a first modern assessment of Quaternary environmental change in the Maltese Islands.     

Evidence of extreme wave events from boulder deposits on the south-east coast of Malta (Central Mediterranean)

Large boulder accumulations have been observed on various coasts bordering the Mediterranean and have been associated with extreme wave events such as powerful storms or tsunamis. This study provides an in-depth analysis of 430 boulder deposits, located along a 3.5 km stretch of rocky coast situated on the SE of the Maltese Islands. It includes a geomorphometric analysis of the observed boulders and use of numerical modelling to estimate wave height required to initiate boulder movement. Comparisons of aerial imagery over a period of 46 years have made it possible to identify boulder movement that could only be attributed to storm waves, given that no local tsunamigenic event has been recorded over this time period. Positioned in the central Mediterranean, the Maltese Islands are exposed to potential tsunamis generated by seismic activity associated with the Malta Escarpment, and the Calabrian and Hellenic arcs. Although imprints from historic tsunami impact cannot be excluded, results indicate that the area is exposed to strong storm waves that are capable of displacing some of the very large boulders observed on site.     

Assessment of LULC and climate change on the hydrology of Ashti Catchment,India using VIC model

The assessment of land use land cover (LULC) and climate change over the hydrology of a catchment has become inevitable and is an essential aspect to understand the water resources-related problems within the catchment. For large catchments, mesoscale models such as variable infiltration capacity (VIC) model are required for appropriate hydrological assessment. In this study, Ashti Catchment (sub-catchment of Godavari Basin in India) is considered as a case study to evaluate the impacts of LULC changes and rainfall trends on the hydrological variables using VIC model. The land cover data and rainfall trends for 40 years (1971–2010) were used as driving input parameters to simulate the hydrological changes over the Ashti Catchment and the results are compared with observed runoff. The good agreement between observed and simulated streamflows emphasises that the VIC model is able to evaluate the hydrological changes within the major catchment, satisfactorily. Further, the study shows that evapotranspiration is predominantly governed by the vegetation classes. Evapotranspiration is higher for the forest cover as compared to the evapotranspiration for shrubland/grassland, as the trees with deeper roots draws the soil moisture from the deeper soil layers. The results show that the spatial extent of change in rainfall trends is small as compared to the total catchment. The hydrological response of the catchment shows that small changes in monsoon rainfall predominantly contribute to runoff, which results in higher changes in runoff as the potential evapotranspiration within the catchments is achieved. The study also emphasises that the hydrological implications of climate change are not very significant on the Ashti Catchment, during the last 40 years (1971–2010).     

Vegetation recovery and landscape change assessment at Chiufenershan landslide area caused by Chichi earthquake in central Taiwan

This study discusses vegetation recovery and land cover change with reference to the Chiufenershan landslide, a major disaster caused by the Chichi earthquake, 21 September 1999. Image classification technology, landscape indicators from multi-temporal remotely sensed data and a field survey provide the data. Image differencing methods and threshold values coupled with pre- and post-quake satellite images were used. Multi-temporal images in combination with various vegetation indices were drawn on to classify land cover patterns and discuss differences and suitability of indices. Landscape indicators and field investigations fed into an investigation of vegetation recovery and landscape change. The study results show that the best image classification system is original wavebands coupled with a cropping management factor index (CMFI). The land cover analysis shows that areas of forest and grass are increasing and areas of landslide are decreasing. From the field investigation, because the left and right sides of the landslide area were not disturbed by the earthquake, their calculated similarity index is the highest (30.08%). Miscanthus floridulus is the most dominant pioneer plant at the landslide collapse area with an importance value index (IVI) of 63.6%.     

Palynological Evidence for Climatic Change and Human Activity during the Holocene on Minorca (Balearic Islands)

Four pollen diagrams from Minorca (Balearic Islands) have been correlated with other previously studied sequences from Majorca and Minorca to define a Holocene landscape sequence for the region from 8000 yr B.P. to the present. The lower part of the pollen diagrams reflects a climatic phase with more rain and less-marked seasonality than today. Significant quantities ofCorylus, Buxus,and mesophilous taxa are found. In the middle part, between 5000 and 4000 yr B.P., a strong change is recorded in composition and structure of the vegetational landscape, with vegetation appearing that was adapted to Mediterranean conditions. This episode coincided with the first human colonization of the island and also with a widespread climatic change in the western Mediterranean region. The change in taxa was complex and some sclerophyllous taxa suchOleaplayed an important role in the transformation of the landscape physiognomy from the mid-Holocene until the present. Although human activities have removed much of the Mediterranean vegetation on the Balearic Islands, it seems clear that the changes have been brought about, in part, by increasing dryness.     

近27a来典型白云岩流域岩溶碳汇变化及其调控机制——以贵州施秉黄洲河流域为例

以贵州省施秉县黄洲河典型白云岩岩溶小流域为例,基于白云石化学平衡热力学方法分别定量估算出1990-1992年、2001-2003年及2016-2018年白云岩流域的年均岩溶碳汇强度,并分析其对气候变化、土地利用调控的响应,结果表明:（1）流域内第二个时段年均有效降雨最大,其次是第一个时段,第三个时段的最小;（2）流域内主要以有林地为主,旱地、建设用地持续增加但增长速率减缓,总体上流域植被覆盖度呈现上升趋势;（3）流域整体的岩溶碳汇强度由大到小依次为2002年、1990年、2016年,水田与旱地对岩溶碳汇贡献较大;（4）气候变化与土地利用共同控制岩溶碳汇,碳汇强度可能不随地类正向演替而增大。      

Evidence of extreme wave events from boulder deposits on the south-east coast of Malta (Central Mediterranean)

Large boulder accumulations have been observed on various coasts bordering the Mediterranean and have been associated with extreme wave events such as powerful storms or tsunamis. This study provides an in-depth analysis of 430 boulder deposits, located along a 3.5 km stretch of rocky coast situated on the SE of the Maltese Islands. It includes a geomorphometric analysis of the observed boulders and use of numerical modelling to estimate wave height required to initiate boulder movement. Comparisons of aerial imagery over a period of 46 years have made it possible to identify boulder movement that could only be attributed to storm waves, given that no local tsunamigenic event has been recorded over this time period. Positioned in the central Mediterranean, the Maltese Islands are exposed to potential tsunamis generated by seismic activity associated with the Malta Escarpment, and the Calabrian and Hellenic arcs. Although imprints from historic tsunami impact cannot be excluded, results indicate that the area is exposed to strong storm waves that are capable of displacing some of the very large boulders observed on site.

     

The relations between land use and karst rocky desertification in a typical karst area,China

Karst rocky desertification (KRD) is one major type of desertification which is under irrational human impact on the vulnerable eco-geo-environment. In this study, Zhudong fengcong rocky desertification landscape was selected to investigate the land use types distribution law in different rock types and the KRD land in different land use types. KRD data was determined by user–computer interactive interpreting method from Aster images in 2004, according to the exposed ratio of rock, the coverage of vegetation and soil in 0.2 km² unit, integrating with land utilizing present situation map, hydrogeology map, relief map, vegetation map, soil distribution map, as well as the practical investigation and the population census datum in 2002. Results showed that the occurrence ratio of KRD land is different in land use types and rocky assemblages obviously; land cover has a strong impact upon KRD. The sloping cropland distributed in homogenous limestone has a higher occurrence ratio of light KRD, secondly, is in the limestone interbedded with clastic rock. Light KRD land was dominated by shrubland, and sloping cropland accounts for 11.67% of it, moderate KRD land was dominated by moderate coverage grass slopes, strong and extremely strong KRD was dominated by rocky dry land which is difficult to use.     

中国过去300年土地利用变化及其气候效应

以两种植被数据为基础,分别利用区域和全球气候模式对过去300年土地利用和地表覆盖变化的气候效应进行了模拟研究。结果表明,耕地面积不断扩大所造成的自然植被破坏可能对区域性气候产生显著影响。通过对不同时期植被特征下地面温度、降水和低层大气环流的比较分析发现,中国东部地区耕地取代自然植被后,全年平均温度有所降低,且存在明显季节差异。植被退化地区的夏季温度有明显升高而冬季温度则显著降低; 同时夏季降水和850hPa风场发生显著变化： 夏季降水明显减少,而这一结果与低层(850hPa)大气环流的反气旋性增强相联系,即植被退化使中国东部夏季风环流减弱,这与目前观测事实是一致的。土地利用引起的地表覆盖的变化可能是东亚季风减弱的原因之一。     

Tholeiitic, calc-alkaline and (?)alkaline igneous rocks of the Shortland Islands, Solomon Islands

The Shortland Islands lie in a northeast-southwest line across the western end of Solomon Islands, immediately adjacent to Bougainville. Three major islands dominate the group.Fauro and surrounding islands, in the northeast, have an altered basement suite comprising tholeiite, icelandite and tholeiitic dacite. This is intruded by a high-level calc-alkaline assemblage of microdiorite, hornblende andesite and rhyodacite and overlain by volcanogenic sandstones derived from an andesitic to dacitic volcano. Pyroclastics comprising high-alumina basalt and pyroxene andesite overlie the volcanogenic sandstones. The tholeiitic basement lavas may be of Late Oligocene to Early Miocene age, and the calc-alkaline rocks are probably also pre-Pliocene in age.Alu, in the centre of the group, also has an altered tholeiitic lava basement, which is intruded by a quartz diorite body and overlain by hypersthene-augite basaltic andesite. Pliocene siltstone and Quaternary shallow marine carbonates cover these igneous rocks over much of the island.Mono, in the southwest, has a small basement exposure of altered pillowed hawaiite, overlain by Miocene pelagic limestone, Pliocene siltstone and Quaternary reef limestone. Isolated clasts of pyroxene andesite and ?benmoreite occur in streams and on beaches.The younger, calc-alkaline suites on all islands were formed in an island arc environment, possibly related to subduction from the southwest beneath the New Britain Trench. The basement lavas on Alu are probably early island arc tholeiites, and both these lavas and the calc-alkaline rocks of Alu share a common trend on variation diagrams. The two igneous suites of Fauro, however, have distinctly different trends. The basement lavas have some chemical similarities with oceanic tholeiites, but an early island arc origin for these lavas cannot be ruled out. The altered hawaiite and benmoreite on Mono probably originated in an oceanic island environment.     

黑河流域陆地-大气相互作用研究的几点思考

陆地和大气之间是相互作用、相互影响的,不仅陆面分布与地表过程对大气变化有着响应过程,而且陆面物理过程、地表特征分布对大气过程也有着重要影响。我国西北地区地形分布极不均匀,是水资源变化和气候变化的敏感区与脆弱地区。这里,由于海拔高度起伏造就了以水为主线的上游山区冰雪、冻土—中游森林、绿洲—下游戈壁荒漠的多个自然景观带共存的内陆河流域,是开展陆—气相互作用研究的理想场所。文章集中黑河流域水循环过程、冰雪/冻土与大气相互作用、降水异质性、人类活动影响以及尺度等问题,阐述了流域研究现状以及研究热点,指出发挥各学科优势,将大尺度的大气过程与中间尺度和小尺度的陆面水文/生态过程结合,建立流域尺度大气—水文—生态过程真正的双向耦合模式,不仅研究气候变化对陆面水文、生态的影响,同时探讨陆面小尺度过程对大气的反馈机理,探索流域尺度的水循环过程和驱动机理,为水资源合理利用提供理论基础。     

An 11 000-year record of vegetation and environment from Lago di Martignano,Latium, Italy

A pollen diagram from Lago di Martignano, a maar lake in central Italy, provides an 11000-year record of vegetation and environment change. The earliest pollen spectra are dominated by Artemisia and Gramineae, representing late glacial steppe vegetation typical of the Mediterranean region. Broad-leaved forests were established by ca. 11 000 yr BP. Although Quercus initially dominated their canopy, a wide range of other mesophyllous trees were also present. Pollen values for sclerophyllous tree and shrub taxa characteristic of Mediterranean woodlands and scrub are initially low (<10%). After ca. 7000 yr BP, however, they begin to increase and rise to a peak of >40% of total land pollen at ca. 6700 yr BP, with Olea europaea the single most abundant taxon. Human influence upon the vegetation only becomes significant somewhat after this peak, with progressive clearance of woodland and expansion of herbaceous communities. Castanea sativa and luglans regia pollen is recorded consistently from the beginning of the rise in pollen values for taxa characteristic of Mediterranean scrub communities. Pollen values for arable crops increase progressively after ca. 5500 yr BP, following the peak pollen values for taxa characteristic of Mediterranean scrub vegetation. Late glacial and Holocene climate changes have been complex in this region, with the present character of the climate developing only during the last millennium. Rates of change of pollen spectra peak during this period.     

1896–2006 Sahelian annual rainfall variability and runoff increase of Sahelian Rivers

Updated rainfall data to 2006 confirm that the Sahelian rainfall has increased since the end of the 1990s, but the annual average rainfall is still as low as during the drought of the 1970s. The decrease of rainfall is higher in the Northwest and lower in the Southeast Sahel. The increase of temperature over West Africa during the end of the 20th century induced an increase of Potential Evaporation, which might reduce the runoff. However, the joint effect of climate change and of human activities on land cover over more than three decades is responsible for an increase of the runoff coefficients of the West African Sahelian Rivers since the 1970s, despite the rainfall shortage during the same period, as revealed by the analysis of runoff from Mauritania, Burkina-Faso and Niger. The runoff coefficients have increased in regions with less than 750 mm of annual rainfall, under Sahelian and subdesertic climates, leading to increased flood peaks, occurring earlier in the season. Even if it is difficult to separate which part of this runoff coefficient increase is due to climate change alone or to human impact on land cover, the highest values are observed in the most inhabited areas, where land cover is dominated by cultivated areas. This climatic/human impact on land cover is so huge that it has changed since decades the hydrological regimes of the Sahelian Rivers, from the small watershed to the largest one, such as the Niger River at Niamey.     

Dynamics of land use/cover changes and the analysis of landscape fragmentation in Dhaka Metropolitan, Bangladesh

Rapid urban expansion due to large scale land use/cover change, particularly in developing countries becomes a matter of concern since urbanization drives environmental change at multiple scales. Dhaka, the capital of Bangladesh, has been experienced break-neck urban growth in the last few decades that resulted many adverse impacts on the environment. This paper was an attempt to document spatio-temporal pattern of land use/cover changes, and to quantify the landscape structures in Dhaka Metropolitan of Bangladesh. Using multi-temporal remotely sensed data with GIS, dynamics of land use/cover changes was evaluated and a transition matrix was computed to understand the rate and pattern of land use/cover change. Derived land use statistics subsequently integrated with landscape metrics to determine the impact of land use change on landscape fragmentation. Significant changes in land use/cover were noticed in Dhaka over the study period, 1975–2005. Rapid urbanization was manifested by a large reduction of agricultural land since urban built-up area increased from 5,500?ha in 1975 to 20,549?ha in 2005. At the same time, cultivated land decreased from 12,040 to 6,236?ha in the same period. Likewise, wetland and vegetation cover reduced to about 6,027 and 2,812?ha, respectively. Consequently, sharp changes in landscape pattern and composition were observed. The landscape became highly fragmented as a result of rapid increase in the built-up areas. The analysis revealed that mean patch size decreased while the number of patches increased. Landscape diversity declined, urban dominance amplified, and the overall landscape mosaics became more continuous, homogenous and clumped. In order to devise sustainable land use planning and to determine future landscape changes for sound resource management strategies, the present study is expected to have significant implications in rapidly urbanizing cities of the world in delivering baseline information about long term land use change and its impact on landscape structure.     

Natural resources,land use and degradation in the coastal zone of Arauco and the Nahuelbuta Range,Central Chile

Studies of soil, sediments and vegetation cover on the coastal zone and at the Nahuelbuta Range, Province of Arauco, Central Chile, often provide insights into the landscape development and vegetation succession during the Quaternary. The present vegetation reflects the climatic changes operating since the Pleistocene and the degradation brought about by human action since the land opening by colonists. Increasing pressures by timber companies are causing a replacement of the original forests by pines and eucalyptus and the encroachment of crop lands used for the production of staples by Mapuche Indians.     

亚高山不同植被类型区的雨季岩溶溶蚀速率研究

关于岩溶溶蚀速率,前人在研究中肯定了岩溶区内CO2浓度的时空变化对溶蚀速率的驱动作用,然而不同的植被条件产生的土壤理化性质差异和变化对溶蚀速率的方向和强度也具有较大的影响.通过野外溶蚀标准试片法,测试得出重庆金佛山岩溶区碧潭泉和水房泉两泉域4种典型植被类型下的5个测试点的雨季绝对溶蚀量和平均面积溶蚀量.测试结果表明不同植被条件甚至同一植被类型下不同海拔下岩溶区石灰岩标准试片的溶蚀速率都存在较大差异,5个测试点溶蚀量由大到小依次为水房泉竹林地、水房泉林地、水房泉草地、碧潭泉林地、碧潭泉灌草丛.通过测试点的土壤基本理化性质分析得出以下结论:在研究区研究时间内的降雨量、温度差异的基础上,除了土壤CO2浓度,土壤有机质也是控制金佛山两泉域岩溶速率的主要因素之一.     

Monitoring land use/land cover change using multi-temporal Landsat satellite images in an arid environment: a case study of El-Arish,Egypt

Environment in arid conditions is dynamic and needs more investigation to understand the complexity of change. This spatiotemporal study will help to assess and monitor the land use and land cover change in the arid region of El-Arish area, where the climate and human activities are the major threats to rural development. In the past 11 years, dramatic changes of environment have been recorded in case studies. The post-classification comparison method was used to observe the changes using multi-temporal satellite images which were captured in the years 1999, 2001, 2005, and 2010. The overall accuracy of the produced thematic images was assessed regarding to the quantity and allocation disagreements. Five classes were defined in this investigation: bare soil, vegetation, urban, sand dunes, and fertile soil. From the year 1999 to 2010, fertile soil was increased by 13 %. Bare soil class occupied more than 50 % of land in the case study during for over a decade. From year 1999 to 2010, vegetation cover witnessed a dramatic increase. Soil and water management are the keys of land development and positive land use and land cover dynamics. Changing agricultural policies of using the available water resources are needed in the case study to prevent severe food shortage in the future.     

Climate‐controlled aggradation and cyclicity of continental loessic siliciclastic sediments in Asselian–Sakmarian cyclothems,Permian, Hugoton embayment,USA

Siliciclastic intervals in Lower Permian carbonate–siliciclastic cyclothems in western Kansas record climate control on facies progression, deposition and preservation. The 26 000 km² study area comprises seven marine‐continental (carbonate–siliciclastic) cyclothems caused by glacioeustasy. Core data and a three‐dimensional geological model provide a detailed view of the sub‐surface on a gently sloping ramp. Siliciclastic intervals in the cyclothems are fine‐grained red beds with extensive pedogenic features, indicating a continental origin. Bed geometry (sheet‐like deposits that thin to the east), lateral grading, grain size (very fine‐grained sand to silt) and grain angularity (sub‐angular to angular) suggest that the sediment is loess sourced from the west, probably the Ancestral Rocky Mountains. There is a repeated record of glacial‐cycle‐scale, climate‐controlled cyclicity within siliciclastic intervals that has not been recognized previously. Aeolian silt grain size coarsens upward towards the middle, then fines upward in each siliciclastic interval. When sea‐level was high (interglacial) and carbonate production flourished, aeolian sedimentation nearly ceased, suggesting increased vegetation and rainfall at the source. As sea‐level fell, fine‐grained siliciclastic sediments were deposited under relatively dry, but seasonally wet conditions on an exposed ramp. Laterally graded coarser grained siliciclastic sediments with diagnostic fabrics indicate drier conditions with seasonal rainfall during a continued relative fall in sea‐level. The coarsest siliciclastic sediments were deposited during the lowest sea‐level and driest conditions, but still with sufficient seasonal moisture to allow vegetative cover and bioturbation. Subsequent upward fining is correlated with sedimentological indications of wetter conditions during relative sea‐level rise. Unlike common sequence stratigraphic models that relate siliciclastic sediment accumulation to base‐level rise, continental deposits were preserved because plants and pedogenesis stabilized aeolian sediment. The aggradational landscape formed by this process had several metres of positive relief that reduced accommodation for overlying marine carbonate strata. Thus, this mechanism for continental siliciclastic aggradation has a significant effect on sequence stratigraphic architecture.     

A multidisciplinary approach to reveal the Sicily Climate and Environment over the last 20 000 years

We present a thorough review of the knowledge on the climate and environment in Sicily over the last 20 000 years, taking into account results of several studies carried using terrestrial and marine records. We obtain a coherent framework of the most important changes succeeded in the island, even if some points need further investigation. All the reconstructions of surface temperatures of the seas and the air surrounding Sicily point out severe climatic conditions during the last glacial period. The steppe- and semisteppe-like vegetation pattern testifies, together with additional evidence from geochemical data of lacustrine evidence, markedly arid conditions. Fi-nally, significant episodes of sea level drop connected Sicily to the Italian Peninsula and favoured the dispersion of faunal elements from southern Italy. The transition between the last glacial and the Holocene was not characterized by a gradual warming but was punctuated by two abrupt suborbital climatic fluctuations: Bølling-Allerød (warm) and Younger Dryas (cold), as recognized in the sediments recovered close to the northern and southern coast of Sicily. A denser arboreal cover is possibly indicated by the occurrence of dormouse and Arvicola remains. Finally the sensitivity of Sicily to climate perturbations is demonstrated by the occurrence of repeated subtle climatic anomalies during the Holocene, including the Little Ice Age, also known from historical chronicles. Forests, woods and Mediterranean maquis developed in the early-middle Holocene. Thereafter was a general decline of arboreal vegetation, following a general aridification trend that seems to be a common feature in southern Europe and North Africa. Science Greek colonization (7^th century before Christ), the landscape was intensively modelled for agriculture and breeding, leading to a significant loss of vegetation cover.