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151.
Glacier change and glacier runoff variation in the Tuotuo River basin,the source region of Yangtze River in western China 总被引:3,自引:0,他引:3
Glaciers in the Tuotuo River basin, western China, have been monitored in recent decades by applying topographical maps and
high-resolution satellite images. Results indicate that most of glaciers in the Tuotuo River basin have retreated in the period
from 1968/1971 to 2001/2002, and their shrinkage area is 3.2% of the total area in the late 1960s. To assess the influence
of glacier runoff on river runoff, a modified degree–day model including potential clear-sky direct solar radiation has been
applied to the glaciated regions of the river basin over the period 1961–2004. It was found that glacier runoff has increased
in the last 44 years, especially in the 1990s when a two-thirds increase in river runoff was derived from the increase in
glacier runoff caused by loss of ice mass in the entire Tuotuo River basin. 相似文献
152.
For the assessment of shallow landslides triggered by rainfall, the physically based model coupling the infinite slope stability
analysis with the hydrological modeling in nearly saturated soil has commonly been used due to its simplicity. However, in
that model the rainfall infiltration in unsaturated soil could not be reliably simulated because a linear diffusion-type Richards’
equation rather than the complete Richards’ equation was used. In addition, the effect of matric suction on the shear strength
of soil was not actually considered. Therefore, except the shallow landslide in saturated soil due to groundwater table rise,
the shallow landslide induced by the loss in unsaturated shear strength due to the dissipation of matric suction could not
be reliably assessed. In this study, a physically based model capable of assessing shallow landslides in variably saturated
soils is developed by adopting the complete Richards’ equation with the effect of slope angle in the rainfall infiltration
modeling and using the extended Mohr–Coulomb failure criterion to describe the unsaturated shear strength in the soil failure
modeling. The influence of rainfall intensity and duration on shallow landslide is investigated using the developed model.
The result shows that the rainfall intensity and duration seem to have similar influence on shallow landslides respectively
triggered by the increase of positive pore water pressure in saturated soil and induced by the dissipation of matric suction
in unsaturated soil. The rainfall duration threshold decreases with the increase in rainfall intensity, but remains constant
for large rainfall intensity. 相似文献
153.
Mapping susceptibility of rainfall-triggered shallow landslides using a probabilistic approach 总被引:2,自引:0,他引:2
To prepare a landslide susceptibility map is essential to identify hazardous regions, construct appropriate mitigation facilities,
and plan emergency measures for a region prone to landslides triggered by rainfall. The conventional mapping methods require
much information about past landslides records and contributing terrace and rainfall. They also rely heavily on the quantity
and quality of accessible information and subjectively of the map builder. This paper contributes to a systematic and quantitative
assessment of mapping landslide hazards over a region. Geographical Information System is implemented to retrieve relevant
parameters from data layers, including the spatial distribution of transient fluid pressures, which is estimated using the
TRIGRS program. The factor of safety of each pixel in the study region is calculated analytically. Monte Carlo simulation
of random variables is conducted to process the estimation of fluid pressure and factor of safety for multiple times. The
failure probability of each pixel is thus estimated. These procedures of mapping landslide potential are demonstrated in a
case history. The analysis results reveal a positive correlation between landslide probability and accumulated rainfall. This
approach gives simulation results compared to field records. The location and size of actual landslide are well predicted.
An explanation for some of the inconsistencies is also provided to emphasize the importance of site information on the accuracy
of mapping results. 相似文献
154.
This study presents a laboratory study of the following two aspects: (1) the influence of sea laver treatment acid on the
geoenvironmental properties of Ariake Sea tidal mud, and (2) the natural remediation effect on the sea laver treatment acid
contaminated Ariake Sea tidal mud caused by the upward seepage of pore water liquid in the mud. Firstly, the mechanisms of
the transport of sea laver treatment acid in the Ariake Sea tidal mud and the generation mechanisms of the upward seepage
flow in the Ariake Sea tidal mud are discussed. Secondly, a series of one-dimensional laboratory infiltration tests were carried
out to investigate the deterioration of the Ariake Sea tidal mud caused by the sea laver acid treatment practice. Test results
reveal that the acid treatment practice caused considerable change in the geochemical properties of the mud in terms of increase
in sulfide content and decrease in pH value. After the treatment by the sea laver treatment acid, the sulfide content of the
mud even exceeded the safe limit value for the benthos, which represents undesirable living condition for benthos. Thirdly,
series of laboratory fresh seawater infiltration tests for the deteriorated Iida site mud were conducted to illustrate this
natural remediation efficiency. It is found that with the infiltration of the fresh seawater, the sulfide content of the Iida
site mud was considerably reduced and pH value increased to an acceptable range for benthos living in the tidal flat mud.
With the increase in the infiltration time and the hydraulic gradient, the remediation efficiency could be increased. 相似文献
155.
Yuan-Bao Wu Shan Gao Hong-Fei Zhang Sai-Hong Yang Wen-Fang Jiao Yong-Sheng Liu Hong-Lin Yuan 《Contributions to Mineralogy and Petrology》2008,155(1):123-133
The Hong’an area (western Dabie Mountains) is the westernmost terrane in the Qinling-Dabie-Sulu orogen that preserves UHP
eclogites. The ages of the UHP metamorphism have not been well constrained, and thus hinder our understanding of the tectonic
evolution of this area. LA-ICPMS U–Pb age, trace element and Hf isotope compositions of zircons of a granitic gneiss and an
eclogite from the Xinxian UHP unit in the Hong’an area were analyzed to constrain the age of the UHP metamorphism. Most zircons
are unzoned or show sector zoning. They have low trace element concentrations, without significant negative Eu anomalies.
These metamorphic zircons can be further subdivided into two groups according to their U–Pb ages, and trace element and Lu–Hf
isotope compositions. One group with an average age of 239 ± 2 Ma show relatively high and variable HREE contents (527 ≥ LuN ≥ 14) and 176Lu/177Hf ratios (0.00008–0.000931), indicating their growth prior to a great deal of garnet growth in the late stage of continental
subduction. The other group yields an average age of 227 ± 2 Ma, and shows consistent low HREE contents and 176Lu/177Hf ratios, suggesting their growth with concurrent garnet crystallization and/or recrystallization. These two groups of age
are taken as recording the time of prograde HP to UHP and retrograde UHP–HP stages, respectively. A few cores have high Th/U
ratios, high trace element contents, and a clear negative Eu anomaly. These features support a magmatic origin of these zircon
cores. The upper intercept ages of 771 ± 86 and 752 ± 70 Ma for the granitic gneiss and eclogite, respectively, indicate that
their protoliths probably formed as a bimodal suite in rifting zones in the northern margin of the Yangtze Block. Young Hf
model ages (T
DM1) of magmatic cores indicate juvenile (mantle-derived) materials were involved in their protolith formation.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
156.
Shear strength characterization of municipal solid waste at the Suzhou landfill, China 总被引:5,自引:0,他引:5
The current practice of slope stability analysis for a municipal solid waste (MSW) landfill usually overlooks the dependence of waste properties on the fill age or embedment depth. Changes in shear strength of MSW as a function of fill age were investigated by performing field and laboratory studies on the Suzhou landfill in China. The field study included sampling from five boreholes advanced to the bottom of the landfill, cone penetration tests and monitoring of pore fluid pressures. Twenty-six borehole samples representative of different fill ages (0 to 13 years) were used to perform drained triaxial compression tests. The field and laboratory study showed that the waste body in the landfill can be sub-divided into several strata corresponding to different ranges of fill age. Each of the waste strata has individual composition and shear strength characteristics. The triaxial test results showed that the MSW samples exhibited a strain-hardening and contractive behavior. As the fill age of the waste increased from 1.7 years to 11 years, the cohesion mobilized at a strain level of 10% was found to decrease from 23.3 kPa to 0 kPa, and the mobilized friction angle at the same strain level increasing from 9.9° to 26°. For a confinement stress level greater than 50 kPa, the shear strength of the recently-placed MSW seemed to be lower than that of the older MSW. This behavior was consistent with the cone penetration test results. The field measurement of pore pressures revealed a perched leachate mound above an intermediate cover of soils and a substantial leachate mound near the bottom of the landfill. The measurements of shear strength properties and pore pressures were utilized to assess the slope stability of the Suzhou landfill. 相似文献
157.
Assessment of disaster resilience capacity of hillslope communities with high risk for geological hazards 总被引:2,自引:0,他引:2
Su-Chin Chen Jhy-Wei Ferng Yu-Ting Wang Ting-Yeh Wu Jieh-Jiuh Wang 《Engineering Geology》2008,98(3-4):86-101
This study presents a novel preparedness assessment method for assessing hazard mitigation and environmental planning of hillslope communities. A professional questionnaire was utilized to weight each indicator. Communities in Hsinchu, Taichung and Nantou counties with debris flow hazards were taken as study samples. Debris flow risk and landslide susceptibility for each community were determined using Geographic Information System (GIS) technology and logistic regression analysis. Thus, a novel risk assessment method for evaluating disaster resilience capacity of hillslope communities was established. This method was then applied to assess casualties caused by Typhoon Herb in 1996 and Typhoon Mindulle in 2004. Additionally, the analytical results generated by this assessment method were discussed with the aim of developing references for implementation of risk analysis, increasing the effectiveness of disaster mitigation, and reducing future loss of life and property. 相似文献
158.
The alkenone unsaturation index UK′37 has been applied to reconstruct past temperature changes in both marine and lacustrine systems. However, few studies have addressed whether the relative abundance of the C37:4 alkenone to the total C37 production (%C37:4) can reflect surface salinity changes in lacustrine systems. Here we present long-chain C37 alkenone distribution patterns in surface sediments from Lake Qinghai, China. Surface sediments were sampled over a large range of surface salinity changes (1.7-25 g/l) within Lake Qinghai and its surrounding lakes, while temperature differences at these sampling locations should be relatively small. We have found that %C37:4 varies from 15% to 49% as surface salinity decreases. We tentatively describe this %C37:4-salinity link with a general linear regression: %C37:4 = 53.4 (±7.8) − 1.73 (±0.45) × S (n = 28, r2 = 0.62), although step-wise %C37:4 changes in response to salinity variation may exist. UK′37 values vary between 0.10 and 0.16 at these sites and the inferred range of lake water temperature changes is ∼2-3 °C, suggesting that UK′37 largely reflects temperature signal across a large salinity range, consistent with previous findings that UK′37 can indicate temperature changes over a large diversity of environmental settings. We have also found that UK′37 values are correlated with salinity changes (r2 = 0.4), and thus cannot exclude potential temperature effect on %C37:4 and salinity effect on UK′37 in this study. However, even extreme estimates of temperature differences within the lake are still unable to explain the observed %C37:4 changes. We therefore suggest that %C37:4 could be used to infer past lake salinity changes at a regional scale. 相似文献
159.
Silicon isotope fractionation in bamboo and its significance to the biogeochemical cycle of silicon 总被引:2,自引:0,他引:2
A systematic investigation on silica contents and silicon isotope compositions of bamboos was undertaken. Seven bamboo plants and related soils were collected from seven locations in China. The roots, stem, branch and leaves for each plant were sampled and their silica contents and silicon isotope compositions were determined. The silica contents and silicon isotope compositions of bulk and water-soluble fraction of soils were also measured. The silica contents of studied bamboo organs vary from 0.30% to 9.95%. Within bamboo plant the silica contents show an increasing trend from stem, through branch, to leaves. In bamboo roots the silica is exclusively in the endodermis cells, but in stem, branch and leaves, the silica is accumulated mainly in epidermal cells. The silicon isotope compositions of bamboos exhibit significant variation, from −2.3‰ to 1.8‰, and large and systematic silicon isotope fractionation was observed within each bamboo. The δ30Si values decrease from roots to stem, but then increase from stem, through branch, to leaves. The ranges of δ30Si values within each bamboo vary from 1.0‰ to 3.3‰. Considering the total range of silicon isotope composition in terrestrial samples is only 7‰, the observed silicon isotope variation in single bamboo is significant and remarkable. This kind of silicon isotope variation might be caused by isotope fractionation in a Rayleigh process when SiO2 precipitated in stem, branches and leaves gradually from plant fluid. In this process the Si isotope fractionation factor between dissolved Si and precipitated Si in bamboo (αpre-sol) is estimated to be 0.9981. However, other factors should be considered to explain the decrease of δ30Si value from roots to stem, including larger ratio of dissolved H4SiO4 to precipitated SiO2 in roots than in stem. There is a positive correlation between the δ30Si values of water-soluble fractions in soils and those of bulk bamboos, indicating that the dissolved silicon in pore water and phytoliths in soil is the direct sources of silicon taken up by bamboo roots. A biochemical silicon isotope fractionation exists in process of silicon uptake by bamboo roots. Its silicon isotope fractionation factor (αbam-wa) is estimated to be 0.9988. Considering the distribution patterns of SiO2 contents and δ30Si values among different bamboo organs, evapotranspiration may be the driving force for an upward flow of a silicon-bearing fluid and silica precipitation. Passive silicon uptake and transportation may be important for bamboo, although the role of active uptake of silicic acid by roots may not be neglected. The samples with relatively high δ30Si values all grew in soils showing high content of organic materials. In contrast, the samples with relatively low δ30Si values all grew in soil showing low content of organic materials. The silicon isotope composition of bamboo may reflect the local soil type and growth conditions. Our study suggests that bamboos may play an important role in global silicon cycle. 相似文献
160.
The altitude effect on the isotopic composition of precipitation and its application to paleoelevation reconstruction using authigenic or pedogenic minerals have been intensively studied. However, there are still no studies on variations in biomarker δD along altitude transects to investigate its potential as a paleoelevation indicator, although it has been observed that δD of higher plant lipid may record changes in precipitation δD (δDp). Here, we present δD values of higher plant-derived C27, C29, and C31n-alkanes from surface soil along the eastern slope of Mount Gongga, China with great changes in physical variables and vegetation over a range from 1000 to 4000 m above sea level. The weighted-mean δD values of these n-alkanes (δDwax) show significant linear correlations with predicted δDp values (R2 = 0.76) with an apparent isotopic enrichment (εwax-p) of −137 ± 9‰, indicating that soil δDwax values track overall δDp variation along the entire altitudinal transect. Leaf δDwax is also highly correlated with mountain altitude by a significant quadratic relationship (R2 = 0.80). Evapotranspiration is found declining with altitude, potentially lowering δDwax values at higher elevations. However, this evapotranspiration effect is believed to be largely compensated by the opposing effect of vegetation changes, resulting in less varied εwax-p values over the slope transect. This study therefore confirms the potential of using leaf δDwax to infer paleoelevations, and more generally, to infer the δD of precipitation. 相似文献