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1.
The purpose of this study is to investigate the oasis landscape fragmentation in northwestern China’s arid regions. Landscape
maps of Jinta oasis were compiled by using GIS based on Landsat TM data of 1990 and 2000. Landscape indexes for evaluating
fragmentation are patch area, patch density, corridor density and split index. Results indicated many difference. First, between
the years 1990 and 2000, the landscape fragmentation in Jinta oasis decreased slightly. Second, the area of the matrix decreased
at the class level. The landscape fragmentation of the matrix (bare soil) increased as a result of increased influence of
human activities on matrix and was opposite to the irrigated farmland whose area is larger and more aggregated in 2000 than
in 1990. Third, dense corridor system is one of the most prominent characteristics of the arid regions. It is one of the key
factors resulting in the landscape fragmentation; especially the fragmentation within the same patch types. The corridor density
of irrigated farmland, residential area and forestland were quite large in Jinta oasis both in 1990 and 2000. The pattern
of Jinta oasis is characterized by agricultural oasis embedded in Gobi and in the desert, where the ecosystem was disturbed
strongly by the intense human activities. 相似文献
2.
An experiment was carried out in two soils of oasis farmland and the surrounding desert at the southern periphery of the Gurbantonggut
Desert, in central Asia, to test the effects of land use on soil organic carbon (SOC) stock and carbon efflux in deep soil.
The result showed that although SOC content in the topsoil (0–0.2 m) decreased by 27% after desert soil was cultivated, total
carbon stock within the soil profile (0–2.5 m) increased by 57% due to the significant increase in carbon stock at 0.2- to
2.5-m depth, and carbon efflux also markedly increased at 0- to 0.6-m depth. In the topsoil, the carbon process of the oasis
was mainly dominated by consumption; in the subsoil (0.2–0.6 m) it was likely to be co-dominated by storage and consumption,
and the greatest difference in SOC stock between the two soils also lay in this layer; while in the deep layer (0.6–2.5 m)
of the oasis, with a more stable carbon stock, there was carbon storage dominated. Moreover, carbon stocks in the deep layer
of the two soils contributed about 65% of the total carbon stocks, and correspondingly, microbial activities contributed 71%
to the total microbial activity in the entire soil profile, confirming the importance of carbon cycling in the deep layer.
Desert cultivation in this area may produce unexpectedly high carbon stocks from the whole profile despite carbon loss in
the topsoil. 相似文献
3.
Catchment scale spatial variability of soil salt content in agricultural oasis,Northwest China 总被引:4,自引:0,他引:4
Soil salinization is a serious environmental problem in the world, especially in arid and semi-arid regions. Therefore, estimating
spatial variability of soil salinity plays an important role in environmental sciences. Aiming at the problem of soil salinization
inside an oasis, a case study was carried out at the Sangong River catchment in Xinjiang province, northwest China. Methods
of classical statistics, geostatistics, remote sensing (RS) and geographic information system (GIS) were applied to estimate
the spatial variability of soil salt content in the topsoil (0–20 cm) and its relationship with landscape structure at catchment
scale. The objective of this study was to provide a scientific basis to understand the heterogeneous of spatial distribution
of soil salt content at a large scale. The results revealed that (1) elevation of landform was a key factor for soil salt
content’s spatial variability, and soil salt content had a strong spatial autocorrelation, which was mainly induced by structural
factors. (2) Mapping of soil salt content by Kriging and comparing it with landscape maps showed that area of soil salinization
in old oasis was smaller than that in new oasis, and degree of soil salinization in old oasis was also lower than that in
the new one. Among all landscapes, cropland was mostly affected by salinity, with 38.8% of the cropland in new oasis moderately
affected by soil salinity, and 8.54% in old oasis. 相似文献
4.
5.
青藏高原土壤碳排放研究是评估国家区域碳排放量和预测气候变化所可能导致影响的关键. 首先对青藏高原土壤碳排放的关键性影响因子进行探讨, 并分析了土壤碳排放的时空分布格局变化. 目前青藏高原土壤碳排放研究主要是针对高寒草甸及高寒草地生态系统, 较少涉及高寒荒漠, 研究区域较为分散; 土壤碳排放受到气候环境因素、生物因素及人为因素等多重因素的影响, 其中温度、土壤湿度、土壤区系生物、人为因素及多年冻土退化是最关键的影响因素; 土壤碳排放具有明显的时空变异性, 空间变异性在生物群丛、景观、区域和生物群系四个尺度体现, 时间变异性在日、季、年上体现. 总体而言, 青藏高原土壤碳排放的研究较少, 尤其关于大尺度、长时间序列的研究以及土壤碳排放的机理等方面的研究十分缺乏, 有待于后续加强研究. 相似文献
6.
Dong Xiaofeng Liu Lichen Wang Jianhua Shi Jin Pan Jinghu 《International Journal of Earth Sciences》2009,98(3):651-664
Eco-environmental changes which generally manifest as the ecological landscape changes are mainly affected by natural and
human factors. Through complex interaction, natural factors and human activities alter the landscape structure and decide
the service function of regional ecosystem. With the development of geographical information system (GIS) and satellite remote
sensing (RS) techniques, the researches on quantitative analysis of landscape changes have made great strides forward. In
this paper, the landscape change dynamics in the Weigou River basin have been investigated by the combined use of high-resolution
RS images and GIS techniques. The objectives are to determine the landscape transition rates among landscape types and to
quantify changes of various landscape indexes using FRAGSTATS, one of the spatial pattern analysis programs for categorical
maps. Under man–machine interactive interpretation method, all of the 10-m resolution SPOT + TM images are classified into
six primary types (farmland, forest, grassland, water, construction area and desert) and 12 sub-types based on the interpretation
key which was established based on 1947 filed pictures in the Weigou River basin. A field check on the data accuracy shows
that the total interpretation accuracy approaches 97.53%. Significant land-use change has taken place in the Weigou River
basin over the six years from 1998 to 2004 due to rehabilitation measures. The results show that there has been a notable
decrease in farmland mainly due to conversion to forest and grassland, the landscape heterogeneity and evenness has increased,
and there is a greater connectivity. The dominance of farmland patch has decreased. And hence the ecological environment has
started to develop in a reversing direction. The study of the integration of high-resolution RS images and GIS technique is
an effective approach to analyze the landscape changes at river basin scale. 相似文献
7.
At present, researches on climate change of the Heihe River basin mainly focus on the relationship between basin climate change
and regional water resources, regional desertification and dynamic climatic seasons of sandstorm, but less on climate change
of oasis region, where there are more intense and frequent human activities. Based on data of precipitation, temperature,
strong wind and dust events frequencies obtained from the six meteorological stations of Zhangye region in Heihe River basin,
the features of climate change during 1968–2005 were carefully studied. Results show that the regional temperature rise rate
exceeded the average level of China. The annual precipitation changed a little, but the precipitation had a slowly increasing
trend in spring and winter. Frequencies of strong wind and sandstorm days show obviously descending trends, which had a close
correlation with the regional temperature rise and the precipitation increase in spring and winter. Meanwhile, further human
economic activities and exploitations to the oasis in the inland valley of arid regions also affected the climate change of
this region, which has a sensitive and fragile eco-environment.
__________
Translated from Journal of Desert Research, 2007, 27(6): 1048–1054 [译自: 中国沙漠] 相似文献
8.
Wei-min Ye Zi-yuan Qi Bao Chen Ji Xie Yu Huang Yao-ru Lu Yu-Jun Cui 《Environmental Earth Sciences》2011,64(1):269-276
Karst rocky desertification is a process of land degradation involving serious soil erosion, extensive exposure of basement
rocks. It leads to drastic decrease in soil productivity and formation of a desert-like landscape. In this regard, changes
in climatic conditions are the main origin of the soils degradation. Indeed, soils subjected to successive dry/wet cycling
processes caused by climate change develop swelling and shrinkage deformations which can modify their water retention properties,
thus inducing the degradation of soil–water capacity. The ecological characteristics of cultivation soils in karst areas,
Southwest of China, are extremely easy to be affected by external environmental factors due to its shallow bedding and low
vegetation coverage. Based on the analysis of the climate (precipitation) of this region during the past decades, an experimental
study has been conducted on a cultivated soil obtained from the typical karst area in southwestern China. Firstly, the soil–water
properties have been investigated. The measured soil–water retention curve shows that the air-entry value of the soil is between
50 and 60 kPa, while the residual saturation is about 12%. Based on the experimental results, three identifiable stages of
de-saturation have been defined. Secondly, a special apparatus was developed to investigate the volume change behavior of
the soil with controlled suction cycles. The vapor equilibrium technique was used for the suction control. The obtained results
show that under the effect of dry/wet cycles, (1) the void ratio of the cultivated soil is continuously decreasing, leading
to a gradual soil compaction. (2) The permeability decreases, giving rise to a deterioration of water transfer ability as
well as a deterioration of soil–water retention capacity. It is then obvious that the long-term dry/wet cycling process caused
by the climate change induce a continuously compaction and degradation of the cultivated soil in karst rocky desertification
areas. 相似文献
9.
沙漠—绿洲过渡带近地表风沙过程研究进展 总被引:1,自引:0,他引:1
受绿洲和沙漠景观格局的双重影响,沙漠—绿洲过渡带是一个对外界条件变化极为敏感的生态环境脆弱带。沙漠—绿洲过渡带近地表风沙过程及其动态演变直接影响绿洲的稳定和有序发展,在空间上制约沙漠的进退或绿洲的变迁。从沙漠—绿洲过渡带局地小气候、沙尘暴、风沙环境、土壤风蚀、风沙输移和绿洲防护体系建设等几个方面比较全面地综述了近数十年来沙漠—绿洲过渡带近地表风沙过程研究进展,并基于当前沙漠—绿洲过渡带生态环境建设与地方需要等面临的实际问题,分析了该领域今后的研究重点和发展趋势。 相似文献
10.
Quanlin Ma Jihe Wang Xinrong Li Shujuan Zhu Hujun Liu Kejie Zhan 《Environmental Earth Sciences》2009,59(4):765-774
The Oasis-desert ecotone plays an important role in ensuring oasis ecological security. This study was to determine the main
factors on the changes of desert vegetation in the oasis-desert ecotone, and to understand the mechanisms of the long-term
changes. During past 50 years, the dominant plant species of Tamarix-vegetation in the Minqin oasis-desert ecotone changed from mesophytes to xerophytes and finally to super-xerophytes. The vegetative
distribution area (belt width of Tamarix-vegetation between desert and oasis) markedly decreased from 1,000 m past to 30 m current. The coverage of Tamarix bushes reduced from 25 to 7%. The importance value (IV) of the bushes fell from 0.957 to 0.752, and Simpson index decreased from 0.702 in 1959–0.589 in 1992, and then increased
to 0.712 in 2002. These changes in vegetation were closely related with the rapid decrease of groundwater table and the reduction
of soil moisture due to unsustainable use of water resources for expanded agriculture development. These findings suggested
that the change of Tamarix-vegetation in the oasis-desert ecotone was a process of vegetation degradation and concurrent desertification. The maintaining
of stable groundwater and Tamarix-vegetation is a vital prerequisite for dryland management, especially, conserving ecological health of oasis-desert systems. 相似文献
11.
Ming Zhao Ke Jie Zhan Guo Yu Qiu Er Tian Fang Zi Hui Yang Yin Chang Zhang Ai De Li 《Environmental Earth Sciences》2011,62(2):403-410
The height profile of sand-dust flux at 0–2.0-m has been well studied. However, there have been very few experimental studies
in the 0–50-m layer. In this study, the height profile of sand-dust flux at 0–50-m was observed by using three sandstorm observation
towers (50 m in height) in 2006. The towers were located at three sites with different vegetation conditions (desert, edge
of an oasis, and oasis) in the Minqin region, a typical desert-oasis area in China. At the same time, the features of the
underlying vegetation were investigated. Results indicated that in the 0–50-m layer, sand-dust flux decreased rapidly as height
rose at the desert and the edge of oasis sites, whereas it increased slightly as height rose in the oasis site. At the three
sites sand-dust fluxes at each height increased with wind velocity, and there was a fairly good exponential relationship among
them. In 2006, a total of 19 sandstorms occurred. The annual sand-dust that passed through a 1-m-wide, 50-m-high section was
9,169 kg at the desert site, 5,318 kg at the edge of oasis site, and 2,345 kg at the oasis site. Compared with the desert
site, the annual sand flux was lower by 42% at the edge of oasis site and 74% at the oasis site. Vegetation had a significant
effect in reducing the sand-dust flux. 相似文献
12.
荒漠化是指人类历史时期以来,由于人类不合理的经济活动和脆弱生态环境相互作用造成土地生产力下降,土地资源丧失,地表呈现类似荒漠景观的土地退化过程。在中国北方荒漠化形成因素中过度放牧占30.1%,过度农垦占26.9%,过度樵采占32.7%,水资源利用不当占96%,工矿交通建设中不注意环境保护占0.7%,在地区上以北方农牧交错及旱农地区荒漠化最为严重。要采取因地制宜措施和建立健全而完善的治理实施系统以达到生态、经济和社会三个效益的目的。 相似文献
13.
绿洲演变及其调控因素初析 总被引:33,自引:0,他引:33
绿洲是荒漠区适宜多种生物共同生息繁衍的地域。它通过人为干扰、气候波动和构造活动等因素的变化调控而发生演变。构造活动对绿洲演变的影响具有空间差异性和时间滞后性;气候波动则表现为区域相对一致性, 随时间发展的渐变性和过程的复杂性;人为干扰无论是空间上还是时段上都有很强的局限性, 但其发展迅速和时空不稳定性(社会原因)成为影响绿洲演变的调控因素, 同时也是人工干预绿洲演变, 实施永序管理的重要途径。 相似文献
14.
15.
Heavy metals pollution and the identification of their sources in soil over Xiaoqinling gold-mining region,Shaanxi, China 总被引:1,自引:0,他引:1
Yaoguo Wu Youning Xu Jianghua Zhang Sihai Hu Kai Liu 《Environmental Earth Sciences》2011,64(6):1585-1592
In order to determine the characteristics of heavy metals’ pollution and identify their sources in the soil over the Xiaoqinling
gold-mining region, Shaanxi, China, 133 soil samples were collected over the region, one sample was from a close point as
background, and concentrations of Hg, Pb, Cu, and As in all samples were analyzed. Results indicated that the soil was polluted
by these heavy metals, as their concentrations in the soil over the studied region were higher than that in the background
zone. In addition, the result indicated that these metals had their specific spatial characteristics. Among the samples, those
with higher concentrations of Hg, Pb, and Cu were mainly collected from the Shuangqiao river alluvial terrace area, the loess
ravine tableland, and the piedmont alluvial–pluvial inclined tableland, which are the areas of gold-mining activities. Meanwhile,
the samples with higher concentrations of As were distributed over the loess ravine tableland around Tongguan County, where
agricultural activities were conducted intensively. Furthermore, the sources for all the heavy metals Hg, Pb, Cu, and As in
the soil over each landscape were determined through analyzing the concentration correlation of these metals and comparing
the maps of metal concentration distribution and land-use types. In Yellow river–Weihe river alluvial plain area, these heavy
metals were mainly from agricultural activities. In the other landscapes, As was also mainly from agricultural activities;
the other metals were contrarily from the gold-related activities. Interestingly, the correlation coefficients of As concentrations
with Hg, Pb or Cu concentrations were positive in the samples from Yellow river–Weihe river alluvial plain area, and on the
contrary, they were negative in the samples from the other landscapes. This result showed that the correlation can be used
as an index to indicate properly the effect of the gold-related or agricultural activities on the heavy metals in the soil
and identify their main sources over each landscape. As human activities resulted in the site-specific characteristics in
the concentrations and sources of the heavy metals in each landscape, site-specific control strategies should be selected
intensively to remedy landscape soil pollution. In Yellow river–Weihe river plain area, effective control strategies should
be aimed at remedying As pollution caused by agricultural activities; in the other landscapes, Hg, Pb and Cu pollution caused
by gold-mining activities should be considered. 相似文献
16.
Based on the Landsat TM data in 1988 and 2002, the GIS technique and Fragstats software were used to calculate the land use
conversion matrix and eight landscape metrics at landscape and patch class levels in upstream, midstream, and downstream regions
of Nenjiang River basin. The characteristics of land use and landscape pattern changes in each region during 1988–2002 were
analyzed. The results show the followings: 1) During the period from 1988 to 2002, farmland and construction land area increased,
while the areas of forestland, grassland, and unutilized land decreased in all three regions. The conversion trends from forestland
and grassland to farmland were obvious. The conversion from forestland to farmland mainly occurred in the upstream region,
whereas the conversion from grassland to farmland primarily occurred in the midstream and downstream regions. 2) The water
area in the upstream and midstream regions enlarged, mainly due to the increase of water impounded area as a result of the
construction of reservoirs. Comparatively, the water area in the downstream region decreased, and it mainly occurred in the
east part of downstream region with concentrated lakes and swamps. 3) The degree of landscape fragmentation increased in each
region. The controlling ability of forestland was weakened, and its patch shape became more complicated. In contrast, the
controlling ability of farmland was reinforced, and the connectivity among patches increased. 4) The landscape pattern shows
some gradient features. From the upstream to downstream regions, the disturbance of human activities on dominant patches was
intensified, and consequently, the landscape fragmentation extent and heterogeneity were enhanced. 相似文献
17.
Monitoring land use change at a small watershed scale on the Loess Plateau, China: applications of landscape metrics, remote sensing and GIS 总被引:2,自引:2,他引:0
Delin Liu Bicheng Li Xianzhao Liu D. N. Warrington 《Environmental Earth Sciences》2011,64(8):2229-2239
Rapid land use change has taken place in many arid and semi-arid regions of China including the Loess Plateau. In this study,
changes in land use and landscape fragmentation in the small Shanghuang watershed on the Loess Plateau were investigated by
the combined use of remote sensing, GIS and landscape metrics. Land use classes were mapped and analyzed from a time series
of maps and remotely sensed images that were ground truthed in 2008. Analyses of the data showed that land use had undergone
substantial changes in this small watershed from 1982 to 2008, and these changes could be divided into three phases according
to the change in the landscape matrix whereby the dominant land use was grassland (1982–1990), cropland (1990–2002) and forestland
(2002–2008). During each phase, conversions between different land use types took place frequently, especially among cropland,
orchards, grassland and forestland. Landscape fragmentation increased from 1982 to 1990 and then decreased from 1990 to 2008
as indicated by four landscape metrics. These changes in land use and landscape fragmentation in this small watershed were
mainly controlled by human factors (land management, construction, population pressure, and government policy) rather than
natural factors. 相似文献
18.
LI Baosheng David Dian ZHANG ZHOU Xingjia ZHU Feng YUAN Baoyin MU Guijin LI Sen YAN Mancun JIN Heling GAO Quanzhou SUN Wu 《《地质学报》英文版》2002,76(2):221-228
Based on investigation of sediments in the Yutian-Hotan Oasis at the southern margin of the Tarim basin, 14C ages and grain-size and chemical element analyses, the following views are put forward in this paper.(1) Sediments in the Yutian-Hotan Oasis are composed chiefly of "oasis soil", similar to the recent oasis soil, i.e. brown desert soil, which was formed due to pedogenesis after aeolian sand (sandy loam) and dust (loess) of 3.32-6.64 were deposited.(2) The ancient Yutian-Hotan Oasis represented by oasis soil was formed at 13000 a B.P. During the cold period of the past 13000 years, this region is characterized mainly by accumulation of sand and dust storms, and sandy oasis soil was developed in this region due to pedogenesis in an oasis environment; during the warm period, dust falls predominated along with certain current concomitants (lacustrine facies), and silty oasis soil was formed by pedogenesis. Owing to fluctuations of cold and warm climates since 13000 a B.P., sandy oasis soil was deposi 相似文献
19.
干旱内陆流域景观格局变化下的景观土壤有机碳与氮源汇变化 总被引:2,自引:2,他引:2
以黑河流域中游绿洲区域为例,近10年来,在干旱内陆流域受人类活动强烈影响的区域,景观的破碎度降低,景观异质性减弱,显著的景观变化表现在:耕种景观与荒漠化景观的扩张和沼泽草甸景观与水域景观的萎缩,其中荒漠草原景观面积的10%、山地草原景观的49.8%以及沼泽草甸(包括盐化草甸)景观面积的16.8%演变为耕种景观类型;相反,17.4%的荒漠草原景观面积和20.2%的沼泽草甸退化为沙漠与戈壁景观,另有13.02%的灌耕地面积演变为荒漠草原.景观空间格局演变驱动景观土壤N、C的源汇变化,近10年来,黑河流域中游地区由于景观空间格局变化形成的景观N净排放和有机C净释放分别达到50.65×104T和530.17×104T.山地草原景观的荒漠化与耕种利用、耕种景观的荒漠草原化、沼泽草甸与山地草甸景观以及荒漠草原景观的耕种利用和这些景观的沙漠化发展是造成区域N、C损失的主要途径. 相似文献
20.
Spatial variability of soil moisture at typical alpine meadow and steppe sites in the Qinghai-Tibetan Plateau permafrost region 总被引:2,自引:1,他引:1
Zhaoping Yang Hua Ouyang Xianzhou Zhang Xingliang Xu Caiping Zhou Wenbin Yang 《Environmental Earth Sciences》2011,63(3):477-488
Permafrost degradation has the potential to significantly change soil moisture. The objective of this study was to assess
the variability of soil moisture in a permafrost region using geostatistical techniques. The experiment was conducted in August
2008 in alpine steppe and meadow located in the Qinghai-Tibetan Plateau permafrost region. Four soil depths (0–10, 10–20,
20–30 and 30–40 cm) were analyzed using frequency domain reflectometry, and sampling made of 80 points in a 10 m × 10 m grid
were sampled. Soil moisture was analyzed using classical statistics to appropriately describe central tendency and dispersion,
and then using geostatistics to describe spatial variability. Classical statistical method indicated that soil moisture in
the permafrost region had a normal distribution pattern. Mean surface soil moisture in alpine meadow was higher than that
in alpine steppe. The semivariograms showed that soil moisture variability in alpine cold steppe was larger than that in alpine
meadow, which decreased with depths. Nugget values in alpine steppe were low (0.1–4.5), in contrast to alpine cold meadow.
Soil moisture in alpine steppe had highly structured spatial variability with more than 93.4% spatial heterogeneity, and the
range decreased with depth. Soil moisture content in alpine cold meadow had a moderate spatial dependence with a range of
51.3–169.2 m, increasing with depth. 相似文献