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1.
《山地科学学报》2019,(11)
Soil erosion and land use type have long been viewed as being particularly important drivers of soil degradation. The objectives of this study,therefore, were to select a new soil quality index(SQI)which varies significantly with land use/soil erosion,and to evaluate the new SQI using expert opinion. In total, 18 soil physical, chemical, and biochemical properties(indicators) were measured on 56 soil samples collected from four land use/soil erosion categories(rangeland/surface erosion, rangeland/subsurface erosion, cultivated land/surface erosion and dry-farming land/surface erosion). Principal component and classification analysis(PCCA)identified five PCs that explained 77.7% of the variation in soil properties with the biochemical PC varying significantly with land use/soil erosion.General discriminant analysis(GDA) selected urease and clay as the most sensitive properties distinguishing the land use/soil erosion categories.The GDA canonical scores for the new SQI were significantly correlated with expert opinion soil surface summed scores(for soil movement, surface litter, pedestalling, rills and flow pattern) derivedusing the U.S. Department of the Interior Bureau of Land Management(BLM) method. A forward stepwise general regression model revealed that the new SQI values were explained by soil movement,surface litter, and the summed values of the soil surface factors. Overall, this study confirmed that soil quality in the study area in Iran is controlled by land use and corresponding soil erosion. 相似文献
2.
Numerous studies have reported that treelines are moving to higher elevations and higher latitudes.Most treelines are temperature limited and warmer climate expands the area in which trees are capable of growing.Hence,climate change has been assumed to be the main driver behind this treeline movement.The latest review of treeline studies was published in 2009 by Harsch et al.Since then,a plethora of papers have been published studying local treeline migration.Here we bring together this knowledge through a review of 142 treeline related publications,including 477 study locations.We summarize the information known about factors limiting tree-growth at and near treelines.Treeline migration is not only dependent on favorable growing conditions but also requires seedling establishment and survival above the current treeline.These conditions appear to have become favorable at many locations,particularly so in recent years.The review revealed that at 66%of these treeline sites forest cover had increased in elevational or latitudinal extent.The physical form of treelines influences how likely they are to migrate and can be used as an indicator when predicting future treeline movements.Our analysis also revealed that while a greater percentage of elevational treelines are moving,the latitudinal treelines are capable of moving at greater horizontal speed.This can potentially have substantial impacts on ecosystem carbon storage.To conclude the review,we present the three main hypotheses as to whether ecosystem carbon budgets will be reduced,increased or remain the same due to treeline migration.While the answer still remains under debate,we believe that all three hypotheses are likely to apply depending on the encroached ecosystem.Concerningly,evidence is emerging on how treeline migration may turn tundra landscapes from net sinks to net sources of carbon dioxide in the future. 相似文献
3.
Global climate change has been found to substantially influence the phenology of rangeland, especially on the Tibetan Plateau. However, there is considerable controversy about the trends and causes of rangeland phenology owing to different phenological exploration methods and lack of ground validation. Little is known about the uncertainty in the exploration accuracy of vegetation phenology. Therefore, in this study, we selected a typical alpine rangeland near Damxung national meteorological station as a case study on central Tibetan Plateau, and identified several important sources influencing phenology to better understand their effects on phenological exploration. We found man-made land use was not easily distinguished from natural rangelands, and therefore this may confound phenological response to climate change in the rangeland. Change trends of phenology explored by four methods were similar, but ratio threshold method (RTM) was more suitable for exploring vegetation phenology in terms of the beginning of growing season (BGS) and end of growing season (EGS). However, some adjustments are needed when RTM is used in extreme drought years. MODIS NDVI/EVI dataset was most suitable for exploring vegetation phenology of BGS and EGS. The discrimination capacities of vegetation phenology declined with decreasing resolution of remote sensing images from MODIS to GIMMS AVHRR datasets. Additionally, distinct trends of phenological change rates were indicated in different terrain conditions, with advance of growing season in high altitudes but delay of season in lower altitudes. Therefore, it was necessary to eliminate interference of complex terrain and man-made land use to ensure the representativeness of natural vegetation. Moreover, selecting the appropriate method to explore rangelands and fully considering the impact of topography are important to accurately analyze the effects of climate change on vegetation phenology. 相似文献
4.
This paper inquires firstly into the influence of environmental potential population on population movements in China. We think that there are intimate relationships between the changes of the environmental potential population and the population movements: from southeast to northwest, from the coastland to the borderland in the early 30 years of the founding of the People's Republic of China and the reversion of direction of population movements in recent ten years. Then we come to the conclusion that it has been inappropriate for a large-scale population movement of reclaiming and cultivating wasteland, because the actual population has universally surpassed the environmental potential population in most areas of China. But it is still appropriate and necessary for these movements, such as intelligence or science migration of population, limited population movement within the area of some provinces, population concentration on small towns and temporary fluidity of population. 相似文献
5.
多元指标的海上溢油信息提取 总被引：1，自引：0，他引：1
海上溢油给海洋生态环境带来了巨大的影响,甚至需要几十年才能恢复。运用卫星遥感进行海上溢油监测已成为目前溢油监测的主要手段。本文对海上溢油遥感监测方法进行了分析,鉴此,提出了一种SAR数据的多元指标溢油信息提取方法。首先,对图像进行分割,然后,建立溢油形状参数、纹理特征指数、物理特性指数等主要指标,并以层次分析法得出每一类指标的权重。针对每一类指标,以经现场验证的溢油图像为基础,选择形状参数,如周长与面积比值、复杂度等,建立溢油形状判读等级;选择纹理特征参数,以灰度共生矩阵的相关性、熵、变化等来表达溢油的纹理特性,建立溢油纹理特征判断等级;选择溢油物理特征,如溢油与海水的标准差、均方根差、对比度等,建立溢油物理参数判断等级。在此基础上,建立海上溢油遥感信息提取指数,计算分割图斑的溢油遥感信息提取指数,以此判断溢油遥感信息提取的置信度,为溢油识别提供依据。 相似文献
6.
Jiangjun Wan Wei Deng Xueqian Song Ying Liu Shaoyao Zhang Yi Su Yafeng Lu 《中国地理科学(英文版)》2018,28(1):153-166
Labor migration to urban centers is a common phenomenon in the Panxi region of the southwestern mountainous region of China, mainly owing to inadequate livelihood capital in rural areas. Numerous studies have been conducted to explore the relationship between labor migration and its causes, such as individual and family characteristics, but few studies have focused on livelihood capital. This paper examines the impact factors on labor migration employment location selection and duration from a household livelihood capital perspective. A case study of 279 households from 10 villages in the area was carried out in February 2016. We used both qualitative and quantitative methods to analyze the data. On the basis of the 279 questionnaires, the proportion of households with non-labor migration is 48.4%, whereas households with labor migration within a local city and migration across regions account for 28.7% and 22.9%, respectively. Social, financial, and human capitals are the primary factors that influence migrants’ employment location choice positively. Among them, social capital has a significant impact on both migration within a local city and across regions; each of the regression coefficients is 1.111 and 1.183. Social, human, and financial capitals also have a positive impact on the duration of labor migration, and similarly, social capital is the highest coefficient with 2.489. However, physical capital only partly impacts labor migration across regions, whereas the impact of labor migration within a local city, and the duration, are not significant. Furthermore, the impact of household natural capital on migration space and time are all negative relationships, especially for labor migration across the regions and duration, with coefficient scores of 4.836 and 3.450, respectively. That is to say, a laborer is inclined to migrate within a local city for a short term, or not migrate at all, if natural capital is abundant. Our analysis results show that household livelihood capital has a strong spatio-temporal impact on labor migration. 相似文献
7.
Relationships between environmental and social factors have long been studied by geographers.Nowadays,GIS-aided statistical analysis provides new tools to explore these relationships.In order to detect the impact of topography on social factors,we selected the country of Montenegro as a case example due to its high topographic variability.We compared the spatial pattern of population,settlements and ethnic minorities to physical geographic factors,especially to topography,but lithology and land cover data were also taken into consideration.We found that certain factors are closely correlated,e.g.the settlement density linearly decreases with elevation,while the characteristic settlement area shows an exponential increase upwards.The population density is not related to absolute elevation,but it is in close correlation with height（i.e.elevation relative to the local minimum）.Population change and illiteracy are also topography-related social factors.On the contrary,the variable ethnic pattern of Montenegro is influenced by historical,political and economic effects rather than by environmental factors or topographic features.As a conclusion we state that in the scale of a country or a region,the environment can strongly impact some social factors. 相似文献
8.
Seafloor pockmarks are important indicators of submarine methane seepages and slope instabilities.In order to promote the understanding of submarine pockmarks and their relationship with sediment instabilities and climate changes,here we summarize the research results of pockmarks in the spatio-temporal distributions and shaping factors.Most of pockmarks occur along active or passive continental margins during the last 25 kyr B.P..Circular and ellipse are the most common forms of pockmarks,whereas pockmarks in a special crescent or elongated shape are indicators of slope instabilities,and ring-shape pockmarks are endemic to the gas hydrate zones.Further researches should be focused on the trigger mechanism of climate changes based on the pockmarks in the high latitudes formed during the deglaciation periods,and the role of gas hydrates in the seafloor evolution should be elucidated.In addition,the feature of pockmarks at their early stage(e.g.,developing gas chimneys and gas driving sedimentary doming)and the relations between pockmarks and mass movements,mud diapirs could be further studied to clarify the influences of rapid methane release from submarine sediments on the atmospheric carbon contents. 相似文献
9.
语义轨迹是时空轨迹和语义信息融合的产物。除了含有时空信息以外,语义轨迹包括移动对象自身的运动状态（如速度、方向）、环境（如气温、空间拓扑关系）和社交关系（如好友关系、社交活动）等多方面信息。挖掘语义轨迹可以深入地发现个体或群体移动行为的意图、习惯、情感等高阶语义内容,从而深层次发现个体或群体移动行为的模式、关系和规律等。因而,相较于时空轨迹,语义轨迹在语义性、解释性、可行性等方面更符合决策分析应用的实践需求,具有更重要的研究意义和应用价值。本文对语义轨迹挖掘的关键技术进行了综述。首先,介绍语义轨迹的基本概念,并且根据语义元素类型的不同总结了4种常见的定义形式。其次,归纳了语义轨迹建模的基本阶段,包括预处理、轨迹分段和语义富化。由于语义轨迹无法像时空轨迹那样从位置感知设备中采集获得,因此语义轨迹是通过建模技术得到的,主要通过将语义信息和时空轨迹相融合生成相应的语义轨迹。然后,介绍语义轨迹挖掘的主要任务,包括语义轨迹模式挖掘、语义轨迹聚类、语义轨迹分类、语义轨迹异常检测等。针对每一项挖掘任务,介绍了有关的基本原理和相关算法,总结了主要的关键技术和挑战。最后,探讨了语义轨迹挖掘现存的研究难点和未来研究方向。从模型定义、语义标注技术、多源数据建模等方面,讨论了语义轨迹建模的重要研究问题;从语义轨迹数据管理、分类和预测、流式数据挖掘、隐私保护、多粒度挖掘、评价方法等方面,探讨了语义轨迹挖掘的未来研究问题。 相似文献
10.
Deforestation and other Land Use and Land Cover (LULC) changes, driven by variety of physical and anthropogenic factors, have altered the mountainous environment. Mountains around the world including northern and north western belts of Pakistan are highly sensitive to deforestation and other LULC changes, which have profound impacts on various sectors of bio-physical and socio-economic systems. Assessment of LULC changes has high significance for protection, conservation and monitoring mountainous environment. The present study is an attempt to assess the landscape changes with particular reference to forest cover depletion in Kurram Agency located in the north western mountain belt of Pakistan. For detailed comparative analysis the study area has been divided into three sections, which coincide with the present administrative divisions of the Agency, i.e., Upper, Lower and Central Kurram. Temporal span of this study covers four decades. In this study, land use map of 1970 and land sat satellite imageries of 1987, 2000 and 2014 were used as spatial data sets. The images were processed and classified into six LULC classes through geospatial packages and change detection maps were prepared for each division and time period. Findings of the study reveal two trends in the four major LULC categories. Forest and rangeland have shrunk, on average, by 15% and 7.5% respectively while, bare soil and rocks outcrops have expanded by 89% and agriculture land by 7.2% in Kurram agency. The water bodies and snow cover have minor fluctuation in its land area. Major causes of shrinking greenery is attributed to high influx of Afghan refugees and high energy demand of growing population. However, with outflow of the refugees from Kurram agency the general trend in forest cover has reverted and deforestation rate has slowed down. 相似文献
11.
The adjustment of administrative divisions is one of the important factors guiding China’s urbanization, which has profound economic and social effects for regional development. In this paper, we comprehensively describe the process of the adjustment of administrative divisions at provincial and municipal levels in China and summarize the effects on the basic structure and patterns of the spatial development. We quantitatively assess the effects on fields such as urbanization and social economy through the use of multidimensional scaling. The results show that: 1) Upgrading county to municipality (or city-governed district) is the main way of adjusting the administrative divisions. It is also an important factor in the spatial differentiation of interprovincial urbanization. China’s population urbanization can be divided into four patterns including interprovincial migration, provincial migration, natural growth, and growth caused by the adjustment of administrative divisions, which is also the main reason for the increased Chinese urbanization rate at the provincial level. 2) Taking the city of Beijing as an example, we generalize five adjustment patterns made to administrative divisions: the set-up of sub-districts, the set-up of regional offices, the upgrading of townships to sub-districts, the upgrading of townships to towns, and the set-up of towns and the addition of new regional offices. We summarize the municipal urban spatial structure, including the sub-district office area in the central urban area, the regional office area in the new urban area, the mixed area of villages, towns, and sub-district offices in the suburb area, and the township area in the outer suburb area. 3) The adjustment of administrative divisions triggers a significant circulative accumulation effect, resulting in the spatial locking of population and industrial agglomeration. It affects the evolution of the urban spatial form and plays an important role in shaping the urban spatial structure to move to the characteristic of multicenter. In general, the adjustment of administrative divisions was an important factor affecting the inflated statistical level of urbanization and also an important driving force for the evolution of Chinese urban spatial organization structure. 相似文献
12.
Kirchhoff beam migration is a beam migration method, which focuses on rapid imaging of geological structures. Although this imaging method ignores the amplitude information in the calculation process, it can calculate multi-arrival traveltime. This migration method takes into account both imaging accuracy and computational efficiency. Kirchhoff beam migration employs coarse grid techniques in several key steps such as traveltime calculation, weight function calculation, and imaging calculation. The selection of the coarse mesh size has an important influence on the computational efficiency and imaging accuracy of the migration imaging method. This paper will analyze this influence and illustrate the analysis results by the Marmousi data sets. 相似文献
13.
Ocean-Bottom Node(OBN) acquisitions provide both non-converted and converted reflection energy. There is a clear advantage to independently imaging both P-and S-waves, as they provide more information collectively than either does alone. In many conventional converted-wave pre-stack migration algorithms, density is treated as a constant, which is not the real-life case on earth. S-wave velocity and density information is crucial for hydrocarbon detection because it helps in the identification of porefilling fluids. In this paper, we focused on the effect of density on imaging, and developed a method of reverse-time migration(RTM) on converted s-waves of varying densities(VD-RTMCS). Phase correction was required prior to pre-stack migration to avoid constructive interference between data from adjacent sources. Synthetic data examples showed that when density variations were included, image profiles showed advantages in signal-to-noise ratio, vertical resolution and imaging of complex structures. 相似文献
14.
15.
Spatial distributions and seasonal variations of picoplankton (i.e. Synechococcus spp., Prochlorococcus spp., picoeukaryotes and heterotrophic bacteria) and viruses in the Changjiang estuary have been reported in the past. However,
short-term variations (e.g. at a tidal timescale) of these organisms and their regulating factors remain unclear. We determined
the time-series of fluctuations of picoplankton and viruses with tide simultaneously in flow cytometry in the Changjiang estuary
during a cruise in June 2006, in which a tidal model based rectangle equation was applied. The results indicate that high
cell abundances of picoplankton and viruses occurred during flood tide and low cell abundances during ebb tide. The period
of the surface cell abundance variations was about 13 h, suggesting the surface cell abundances in the Changjiang estuary
were largely regulated by tide. However, cell abundances in middle and bottom waters varied in different periods due to influences
of tidal induced physical forces such as resuspension and stratification. Therefore, tidal action is an important factor for
the diel variations of picoplankton and viruses in the Changjiang estuary. 相似文献
16.
Marcelo Leandro BUENO Vanessa Leite REZENDE Luiza Fonseca A.DE PAULA Joo Augusto Alves MEIRA-NETO José Roberto Rodrigues PINTO Andreza Viana NERI Vanessa PONTARA 《山地科学学报》2021,(5):1192-1207
The campo rupestre sensu lato is a vegetation type that occurs in South American mountains, supports a distinctive flora characterized by high rates of endemism, high herbaceous species richness and often-neglected but also species-rich of the arboreal stratum. We aimed to investigate how environmental factors and elevation are associated with the distribution and diversity of woody species in different rupestrian vegetation types across South America. Using a database of 2,049 woody species from 185 sites across four vegetation types within the campo rupestre, we assessed how the vegetation types were grouped according to their floristic composition and number of shared indicator species, as well as by using different beta diversity indices. The most important variables from a set of 27 variables(e.g. altitude, geo-edaphic and climatic) explaining species distribution were identified using redundancy analysis(RDA) and variation partitioning methods. The distribution of vegetation types was related to both environmental and spatial fractions, with a set of 17 variables retained(e.g. rockiness, grass cover and temperature seasonality as the most important variables). There was an association between the floristic composition of each vegetation type and the elevation range. Although the identified vegetation types are floristically related, they are distinguished by exclusive and habitat-specialist woody species. This uniqueness of vegetation types should be considered in terms of complementarity for the conservation of campos rupestres. 相似文献
17.
在压力-状态-响应(Pressure-State-Response, PSR)模型确立指标体系的基础上,采用灰色关联度分析和熵值赋权相结合的方法,测算出2012年内蒙古贫困地区生态安全综合,压力,状态和响应指数,对研究区生态安全状况进行综合评价;并利用地理空间分析方法和空间分析软件GeoDA对生态安全综合状况进行空间相关性分析,同时结合研究区自然地理特征和社会经济状况,对其生态安全空间格局特征及成因进行诊断性分析.研究发现:(1) 内蒙古贫困地区生态安全水平整体处于一般状态,等级布局具有大聚集,小分散的特点;(2) 生态安全状况分布并非完全随机性,而是表现出空间相似值之间的空间聚集,具有正相关性;(3) 生态安全等级分布状况呈现出区域分异的特点,总体表现为内蒙古西部和东部贫困地区处于一般状态,而中部贫困地区生态安全水平整体处于良好状态,区域内部生态安全水平具有明显的县域差异;(4) 生态安全水平较好的县域和生态安全处于一般水平的县域,压力,状态,响应指标方面差距明显,且影响因素各异. 相似文献
18.
混合像元作为遥感信息的不确定性,一直是定量遥感科学研究的核心领域之一,干旱区由于下垫面均匀、气象条件单一等先天条件,已成为定量遥感产品真实性检验的理想场所。本文以塔里木盆地北缘的库车河绿洲为研究区,首先,针对不同地物类型分别采用不同方法进行地物端元提取;然后,以端元均方根EAR(Endmember Aver-age RMSE,EAR)和最小平均波谱角(Minimum Average Spectral Angle,MASA)值来选取最优端元;最后,用多端元光谱混合分析(Multiple Endmember Spectral Mixture Analysis,MESMA)模型进行光谱混合分解,并对结果作了精度评价与比较分析。结果表明:MESMA模型能有效提高像元内基本组分丰度信息精度,从而为典型地物高精度提取提供了科学方法。 相似文献
19.
１ＩＮＴＲＯＤＵＣＴＩＯＮＮｏｏｎｅｃａｎｄｏｕｂｔｔｈａｔｏｎｅｏｆｔｈｅｍｏｓｔｅｘｃｉｔｉｎｇｓｏｕｎｄｓｉｎｎｉｎｅｔｅｅｎｔｈｃｅｎｔｕｒｙＡｍｅｒｉｃａｗａｓｔｈｅｗｈｉｓｔｌｅｏｆａｌｏｃｏｍｏｔｉｖｅ．ＴｈｒｏｕｇｈｏｕｔｔｈｅｗｈｏｌｅｃｅｎｔｕｒｙｅｓｐｅｃｉａｌｌｙｉｎｔｈｅｓｅｃｏｎｄｈａｌｆｒａｉｌｒｏａｄｓｐｌａｙｅｄａｄｒａｍａｔｉｃｒｏｌｅｉｎｔｒａｎｓｆｏｒｍｉｎｇｔｈｅＡｍｅｒｉｃａｎｗｅｓｔｆｒｏｍａｂａｒｒｅｎｌａｎｄｉｎｔｏａｐｏｐｕｌａｔｅｄｏｎｅ… 相似文献
20.
Aref M. O. AL-JABALI NIE Lei Abdo S. AL-MAQTARY Hussein AL-AKHALI Mohammed HAZAEA Fadel AL-AGHBARI 《世界地质(英文版)》2009,12(1):5-12
According to topography of Yemen, most areas and villages are located at obligated crest, toe of mountain and under cliffs. Therefore Al-Huwayshah consisting of Tawilah sandstone group is characterized by steep slope reach to 90° in some areas. This area is affected by strong tectonic movements and faults that occurred during the geological epochs. This effect enhances to find out fractures and joints as well as the rocks become brittle and ready to slide depending on the position of area. And there are some fractures and joints on the surface of the areas due to tectonic movement associated with opening the Red Sea and Gulf of Aden. The rainfalls, fractures, joints, earthquakes, gravity, vegetations, temperatures and human activities play a big role in the processes of rockfalls and landslides in this area. All those factors are considered as the basic causes and catalyzed factors for occurrence of rockfall in the studide area. In addition, the authors carried out laboratory test for many rock samples to get the physical properties of the rocks. 相似文献