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941.
Desert–oasis ecotone is an interactive area between desert and oasis ecosystems which plays an important role in ensuring
oasis ecological security and maintaining oasis internal stabilization. The studied region had experienced dramatic landscape
change and soil degradation during the 20th century, especially in the last two decades. To document the status and evaluate
this degradation process, geostatistics and GIS map algebra were used to quantify the temporal–spatial changes in landscape
pattern and soil degradation from 1983 to 2005. The results showed that: (1) the change of landscape pattern due to human
activities was the key reason responsible for the increasing of landscape diversity and fragmentation; (2) the extent of soil
degradation was higher near desert ecosystem than oasis, and human activities were the major driving forces in ameliorating
the soil properties; and (3) soil degradation is weaker in regions of bad soil quality than regions of good soil quality due
to both human activities and natural processes. 相似文献
942.
D. Poppe T. Brauers H. -P. Dorn M. Karl T. Mentel E. Schlosser R. Tillmann R. Wegener A. Wahner 《Journal of Atmospheric Chemistry》2007,57(3):203-214
Degradation of isoprene, m-xylene, n-octane, propene, and methacrolein by hydroxyl radicals has been studied in the simulation chamber SAPHIR under burden of
trace gases as they are typical for the moderately polluted planetary boundary layer. Measured time series of the hydrocarbon
mixing ratios and the OH concentrations were used to determine the rate constants. The hydrocarbons were measured with gas
chromatography and proton transfer reaction mass spectrometry. OH was measured with the Jülich DOAS (differential optical
absorption spectroscopy) instrument. In all cases except methacrolein good agreement was found with the reference rate constants
taken from the Master Chemical Mechanism (MCM3.1). The data for methacrolein are consistent with the results of Karl et al.
(J. Atmos. Chem 55, 2006, doi:) who reported a 12% smaller value. The degradation of hydrocarbons provides an independent method to analyse precision and
accuracy of the OH measurements. A precision of better than 4% over a period of nearly 4 months was found. The accuracy is
within the limitations given by the light absorption cross section of OH. Both results are consistent with earlier results
by Hausmann et al. (J. Geophys. Res. 102:16011–16022, 1997). 相似文献
943.
Karol Kuliński Joanna Święta-Musznicka Andrzej Staniszewski Janusz Pempkowiak Małgorzata Latałowa 《Journal of Paleolimnology》2007,38(4):555-567
The quantity and quality of lignin phenols (Σ8, Λ, S/V, C/V and (Ad/Al)v) in the sediments of three small Lobelia lakes with neither inlets nor outlets were investigated and compared with palynological data and lithology of the profiles.
The method of alkaline CuO oxidation was used. Substantial differences with respect to sedimentary lignin concentration and
provenance recorded along the profiles and among the sites are in good agreement with pollen data describing the dominant
type of vegetation and with indices of soil erosion in the lakes’ catchments. This relation shows that the compositions of
lignin degradation products in these lakes are closely related to the local environmental conditions. In all the lakes gymnosperm
wood is the main source of lignin products; however, each lake is characterized by different S/V index values. Especially
good correlations were obtained between pine pollen proportions in sediments and the S/V index. The correlation between the
C/V and (Ad/Al)v indices indicates a higher degradation of organic matter when non-woody tissue is more abundant. This pilot study illustrates
the usefulness and potential for a wider application of lignin oxidation products in palaeoecological reconstructions. This
kind of data would be of special importance when investigating local presence/absence of woody plants and the role of angiosperms/gymnosperms
in local vegetation. Estimates of lignin biodegradation levels, as well as the data on diagenetic processes, may afford supplementary
information on possible disturbances in sedimentation. 相似文献
944.
945.
S. Feyza Cinicioglu Ilknur Bozbey Sadik Oztoprak M. Kubilay Kelesoglu 《Engineering Geology》2007,94(3-4):145-165
This paper presents an integrated, earthquake-damage assessment that standardizes and quantifies methods of analysis. The proposed methodology evaluates all damage-causing phenomena, both individually and in combination. This approach inherently relates to soil-structure interactions by quantifying site-specific geotechnical and structural properties. Specifically considered is ground shaking, the primary damage-causing phenomenon. Also evaluated are the collateral effects of liquefaction, degradation of seismic-bearing capacity and slope failure (landslides). The methodology incorporates a literature-derived probabilistic assessment of damage-causation, and is interpreted and presented as single numbers deemed “Damage Grades.” These damage grades integrate the initial probabilistic evaluation with professional experience and judgment in order to determine potential damage to a particular structure at a particular location. This methodology was applied, with success, to two different locations in Istanbul, Turkey. It should be tested by engineering geologists and geotechnical engineers, for it may be applicable to earthquake-prone areas elsewhere. 相似文献
946.
广西桂林大岩洞岩溶洞穴土壤中有机氯农药的分布特征 总被引:2,自引:0,他引:2
首次对桂林岩溶区洞穴土壤中有机氯农药的污染状况进行了研究。结果表明,洞穴土壤受到了有机氯农药的轻度污染,其中大气传输对有机氯农药的贡献起主导作用。在17种有机氯农药中,以DDTs、HCHs和氯丹污染为主。在洞穴内部OCP总量为1.19~11.18 ng/g,远低于洞外土壤中的含量(11.41~23.62 ng/g)。在洞内土壤中,HCHs含量高于DDTs,在HCH四种同分异构体中,β-HCH占HCHs的比例远高于其他3种同分异构体。除β-HCH外,其他3种同分异构体的含量分布均匀,可能是由洞穴环境稳定、气候分带等因素造成的。在洞外土壤中,异构体百分比和示踪标志物比值表明周围可能有林丹扣三氯杀螨醇的新近输入。研究区六六六和滴滴涕主要来源于历史上使用的农药的残留。 相似文献
947.
Nívea Adriana Dias Pons Osni José Pejon Lázaro Valentin Zuquette 《Environmental Geology》2007,53(4):727-739
This paper presents a methodology for the geological engineering survey of land degradation in urban environments using both remote sensing and geoprocessing tools. The area under study was the city of São Carlos, state of São Paulo, Brazil (urban and expansion area). The data presented here were obtained from earlier studies, photointerpretation and geological engineering mapping. The Envi 4.1 software package was used to prepare the digital orthophotos that served as a reference base for the information. Orthorectification of the Ikonos image (PSM, 1 m) was done and compared with other orthophotos from studies of environmental degradation in urban areas. The evolution of land degradation processes was analyzed based on the photointerpretation of aerial photographs taken on different dates and using Ikonos image. This study allowed to conclude that most of the degradation occurring in the city has been caused by unplanned land occupation, in disregard of environmental conditions, resulting in environmental degradation and thus impacting the quality of life of the urban population. 相似文献
948.
This research integrated selected land degradation indicators (vegetation cover, proportion of drifting sand area, desertification rate, and population pressure) with geo‐information techniques (remote sensing, geographic information system and global positioning system) to assess the severity of land degradation risk. The northern part of Shaanxi province in China was taken as a case study. A computerized land degradation severity assessment was implemented, and ERmapper ver.6.2 and ARC/INFO GIS ver.8.3 environments were used to manage and manipulate thematic data, and to process satellite images and tabular data. Two Landsat TM images in October 1987 and October 1999 were used to produce land use/cover maps of the study area based on the maximum likelihood classification method. These maps were then used to generate land use, land cover change, vegetation degradation and land degradation maps for the study area during the study period, and their corresponding data were integrated into a systematic analysis. Results showed that the overall severity of land degradation in the study area worsened during the study period from 1987 to 1999 with severely, highly and moderately degraded land accounting for 73·8 per cent of the total area. While the area affected by desertification has increased, the rate of desertification has also accelerated to reach 41·5 km2 a?1. Risk of land degradation in the study area has increased, on average, by 39·4 per cent since 1987. Incorporation of both natural and anthropogenic factors in the analysis provided realistic assessment of the risk of desertification. The study area, in general, is exposed to a high risk of land degradation. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
949.
M. Font J.‐L. Lagarde D. Amorese J.‐P. Coutard A. Dubois G. Guillemet J.‐C. Ozouf E. Vedie 《地球表面变化过程与地形》2006,31(14):1731-1745
Physical modelling has been developed in order to simulate the effects of periglacial erosion processes on the degradation of slopes and scarps. Data from 41 experimental freeze–thaw cycles are presented. They attest to the efficiency of periglacial processes that control both erosion and changes in scarp morphology: (i) cryoexpulsion leads to an increase of scarp surface roughness and modifies significantly the internal structure of the active layer; (ii) combined effects of frost creep and gelifluction lead to slow and gradual downslope displacements of the active layer (0·3 cm/cycle); (iii) debris flows are associated with the most significant changes in scarp morphology and are responsible for the highest rate of scarp erosion; (iv) quantification of the erosion rate gives values close to 1 cm3 cm?2 for 41 freeze–thaw cycles. These experimental results are consistent with field data acquired along the La Hague fault scarp (Normandy, France) where an erosion rate of 4·6 ± 1 m3 m?2 per glacial stage has been computed from the volume of natural slope deposits stored during the Weichselian glacial stage. These results show that moist periglacial erosion processes could lead to an underestimation of Plio‐Quaternary deformation in the mid‐latitudes. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
950.
Laurent Bret Yannick Fevre Jean-Lambert Join Bernard Robineau Patrick Bachelery 《Journal of Volcanology and Geothermal Research》2003,123(1-2):25
Piton des Neiges (PN) Volcano on Reunion Island offers a rare opportunity to study deposits related to degradation processes in a deeply eroded oceanic shield volcano. Both the inner parts and flanks reveal a large amount of resedimented volcaniclastic material, including extensive debris avalanche deposits. PN litho–structural units, first studied by Upton and Wadsworth [1965, Philos. Trans. R. Soc. Lond., A 271, pp. 105–130], are re-examined. This review highlights the importance of long volcanic repose periods and erosion processes during PN history. volcaniclastic deposits have been studied in the field in order to evaluate the spatial and temporal distribution of the three main types of PN degradation processes. The deposits of these processes have been classified into: (1) talus, (2) mudflow and debris flow, and (3) debris avalanche. Lithology, frequency and estimated volumes of each deposit type imply that the structural evolution of PN can be considered in terms of the competition between the volcanic productivity and the degradation and erosion processes. The occurrence of huge catastrophic avalanches produced by flank failure is convincingly linked to the basaltic activity of PN, which implies a very low risk at present. On the contrary, mudflows and debris flows pose an important risk due to the high population density focussed around the basin outlets. Moreover, if smaller debris avalanches can occur in the cirques of PN, another major risk must be evaluated. 相似文献