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81.
Hydrologic modelling of the effect of snowmelt and temperature on a mountainous watershed 总被引:2,自引:0,他引:2
Snowmelt-runoff modelling in a mountainous basin is perceived as difficult due to the complexity of simulation. Theoretically, the snowmelt process should be influenced by temperature changes. It is still controversial as how to incorporate the temperature changes into the snowmelt-runoff model in a mountainous basin. This paper presents the results of a study in the North Fork American River basin where the snowmelt-runoff mechanism is modelled by relating the temperature changes to the elevation band in the basin. In this study, a distributed hydrologic model is used to explore the orographic effects on the snowmelt-runoff using the snowfall-snowmelt routine in Soil and Water Assessment Tool (SWAT). Three parameters, namely maximum snowmelt factor, minimum snowmelt factor, and snowpack temperature lag were analysed during the simulation. The model was validated using streamflow data from October 1, 1991 to September 30, 1994 with and without considering the elevation band. The result of this study suggests that the snowmelt-runoff model associated with the elevation band better represents the snowmelt-runoff mechanism in terms of Nash–Sutcliffe coefficient (E NS ), R 2, and Root Mean Square Error (RMSE). 相似文献
82.
The structures of sodium silicate and aluminosilicate glasses quenched from melts at high pressure (6-10 GPa) with varying degrees of polymerization (fractions of nonbridging oxygen) were explored using solid-state NMR [17O and 27Al triple-quantum magic-angle spinning (3QMAS) NMR]. The bond connectivity in melts among four and highly coordinated network polyhedra, such as [4]Al, [5,6]Al, [4]Si, and [5,6]Si, at high pressure is shown to be significantly different from that at ambient pressure. In particular, in the silicate and aluminosilicate melts, the proportion of nonbridging oxygen (NBO) generally decreases with increasing pressure, leading to the formation of new oxygen clusters that include 5- and 6-coordinated Si and Al in addition to 4-coordinated Al and Si, such as [4]Si-O-[5,6]Si, [4]Si-O-[5,6]Al and Na-O-[5,6]Si. While the fractions of [5,6]Al increase with pressure, the magnitude of this increase diminishes with increasing degrees of ambient-pressure polymerization under isobaric conditions. Incorporating the above structural information into models of melt properties reproduces the anomalous pressure-dependence of O2− diffusivity and viscosity often observed in silicate melts. 相似文献
83.
Sequential extraction and leaching characteristics of heavy metals in abandoned tungsten mine tailings sediments 总被引:1,自引:0,他引:1
Pyeong-Koo Lee Min-Ju Kang Ho Young Jo Sang-Hoon Choi 《Environmental Earth Sciences》2012,66(7):1909-1923
The chemical speciation of potentially toxic elements (As, Cd, Cu, Pb, and Zn) in the contaminated soils and sulfides-rich tailings sediments of an abandoned tungsten mine in Korea was evaluated by conducting modified BCR sequential extraction tests. Kinetic and static batch leaching tests were also conducted to evaluate the potential release of As and other heavy metals by acidic rain water and the leaching behaviors of these heavy metals. The major sources of the elements were As-, Zn- and Pb-bearing sulfides, Pb carbonates (i.e., cerussite), and Pb sulfates (i.e., anglesite). The biggest pollutant fraction in these soil and tailing samples consists of metals bound to the oxidizable host phase, which can be released into the environment if conditions become oxidative, and/or to residual fractions. No significant difference in total element concentrations was observed between the tailings sediments and contaminated soils. For both sample types, almost no changes occurred in the mobility of As and the other heavy metals at 7 days, but the mobility increased afterwards until the end of the tests at 30 days, regardless of the initial pH. However, the mobility was approximately 5–10 times higher at initial pH 1.0 than at initial pHs of 3.0 and 5.0. The leached amounts of all the heavy metal contents were higher from tailings sediments than from contaminated soils at pH > 3.0, but were lower at pH < 3.0 except for As. Results of this study suggest that further dissolution of heavy metals from soil and tailing samples may occur during extended rainfall, resulting in a serious threat to surface and groundwater in the mine area. 相似文献
84.
We have characterized the adsorption of Suwannee River humic acid (SRHA) and Cu(II) on calcite from preequilibrated solutions at pH 8.25. Sorption isotherms of SRHA on calcite follow Langmuir-type behavior at SRHA concentrations less than 15 mg C L−1, whereas non-Langmuirian uptake becomes evident at concentrations greater than 15 mg C L−1. The adsorption of SRHA on calcite is rapid and mostly irreversible, with corresponding changes in electrostatic properties. At pH 8.25, Cu(II) uptake by calcite in the presence of dissolved SRHA decreases with increasing dissolved SRHA concentration, suggesting that formation of Cu-SRHA aqueous complexes is the primary factor controlling Cu(II) sorption at the calcite surface under the conditions of our experiments. We also observed that surface-bound SRHA has little influence on Cu(II) uptake by calcite, suggesting that Cu(II) coordinates to calcite surface sites rather than to surface-bound SRHA.Cu K-edge X-ray absorption near edge structure (XANES) and extended X-ray absorption fine-structure (EXAFS) spectroscopic results show that the local coordination of Cu adsorbed at the calcite surface is very similar in the presence and absence of SRHA. Ca backscatterers at ∼3.90 Å indicate that Cu(II) forms tetragonally distorted inner-sphere adsorption complexes in both binary and ternary systems. Subtle differences in the XANES and EXAFS between binary sorption samples and ternary sorption samples, however, prevent us from ruling out the formation of ternary Cu-SRHA surface complexes. Our findings demonstrate that SRHA plays an important role in controlling the fate and transport of Cu(II) in calcite-bearing systems. 相似文献
85.
Andesite and dacite genesis via contrasting processes: the geology and geochemistry of El Valle Volcano,Panama 总被引:3,自引:0,他引:3
Mare J. Defant Lee F. Clark Robert H. Stewart Mark S. Drummond Jelle Z. de Boer René C. Maury Hervé Bellon Thomas E. Jackson Juan F. Restrepo 《Contributions to Mineralogy and Petrology》1991,106(3):309-324
The easternmost stratovolcano along the Central American arc is El Valle volcano, Panama. Several andesitic and dacitic lava
flows, which range in age 5–10 Ma, are termed the old group. After a long period of quiescence (approximately 3.4 Ma), volcanic
activity resumed approximately 1.55 Ma with the emplacement of dacitic domes and the deposition of dacitic pyroclastic flows
0.9–0.2 Ma. These are referred to as the young group. All of the samples analyzed are calc-alkaline andesites and dacites.
The mineralogy of the two groups is distinct; two pyroxenes occur in the old-group rocks but are commonly absent in the young
group. In contrast, amphibole has been found only in the young-group samples. Several disequilibrium features have been observed
in the minerals (e.g., oscillatory zoning within clinopyroxenes). These disequilibrium textures appear to be more prevalent
among the old- as compared with the young-group samples and are most likely the result of magma-mixing, assimilation, and/or
polybaric crystallization. Mass-balance fractionation models for major and trace elements were successful in relating samples
from the old group but failed to show a relationship among the young-group rocks or between the old- and young-group volcanics.
We believe that the old-group volcanics were derived through differentiation processes from basaltic magmas generated within
the mantlewedge. The young group, however, does not appear to be related to more primitive magmas by differentiation. The
young-group samples cannot be related by fractionation including realistic amounts of amphibole. Distinctive geochemical features
of the young group, including La/Yb ratios〉15, Yb〈1, Sr/Y〉150, and Y〈6, suggest that these rocks were derived from the partial
melting of the subducted lithosphere. These characteristics can be explained by the partial melting of a source with residual
garnet and amphibole. Dacitic material with the geochemical characteristics of subducted-lithosphere melting is generated
apparently only where relatively hot crust is subducted, based on recent work. The young dacite-genesis at El Valle volcano
is related to the subduction of relatively hot lithosphere. 相似文献
86.
LEE Ben 《中国地球化学学报》2011,30(2):204-216
The Dehe granitic pluton intruded the Xiahe Group which is in the core complex of the North Qinling Orogenic Belt(NQOB).It shows gneissic bedding and possesses typical S-type granite minerals such as muscovite and garnet.LA-ICP-MS U-Pb isotopic dating of the Dehe granite yielded a weighted average age of 925±23 Ma which represents the emplacement age of the pluton.Most of the εHf(t) values are negative,and the two-stage model ages are consistent with the age of the Qinling Group.The isotope data show that the Dehe granite was formed in the following geological setting:in the syn-collision setting of the NQOB in the Neoproterozoic,crustal thickening induced partial melting of materials derived from the Qinling complex,and then the maga upwelled and intruded into the Xiahe Group.The formation of the Dehe S-type granite implied the occurrence of a convergent event in the QOB during the Neoproterozoic. 相似文献
87.
The accurate determination of surface-layer turbulent fluxes over urban areas is critical to understanding urban boundary layer (UBL) evolution. In this study, a remote-sensing technique using a large aperture scintillometer (LAS) was investigated to estimate surface-layer turbulent fluxes over a highly heterogeneous urban area. The LAS system, with an optical path length of 2.1 km, was deployed in an urban area characterized by a complicated land-use mix (residential houses, water body, bare ground, etc.). The turbulent sensible heat (Q H) and momentum fluxes (τ) were estimated from the scintillation measurements obtained from the LAS system during the cold season. Three-dimensional LAS footprint modeling was introduced to identify the source areas ("footprint") of the estimated turbulent fluxes. The analysis results showed that the LAS-derived turbulent fluxes for the highly heterogeneous urban area revealed reasonable temporal variation during daytime on clear days, in comparison to the land-surface process-resolving numerical modeling. A series of sensitivity tests indicated that the overall uncertainty in the LAS-derived daytime Q H was within 20%-30% in terms of the influence of input parameters and the non-dimensional similarity function for the temperature structure function parameter, while the estimation errors in τ were less sensitive to the factors of influence, except aerodynamic roughness length. The 3D LAS footprint modeling characterized the source areas of the LAS-derived turbulent fluxes in the heterogeneous urban area, revealing that the representative spatial scales of the LAS system deployed with the 2.1 km optical path distance ranged from 0.2 to 2 km2 (a "micro-α scale"), depending on local meteorological conditions. 相似文献
88.
1. Introduction In recent decades, extreme weather events seem to be growing in frequency and risk due to water-related disasters. According to the World Meteorological Or- ganization report (ISDR and WMO, 2004) on World Water Day, 22 March 2004, the economic losses caused by water-related disasters, including floods, droughts and tropical cyclones, are on an increasing trend as follows: the yearly mean in the 1970s was about 131 billion US dollars, 204 billion dollars in the 1980s, and … 相似文献
89.
Variations in the abundance and distribution of pelagic tuna populations have been associated with large-scale climate indices such as the Southern Oscillation Index in the Pacific Ocean and the North Atlantic Oscillation in the Atlantic Ocean. Similarly to the Pacific and Atlantic, variability in the distribution and catch rates of tuna species have also been observed in association with the Indian Ocean Dipole (IOD), a basin-scale pattern of sea surface and subsurface temperatures that affect climate in the Indian Ocean. The environmental processes associated with the IOD that drive variability in tuna populations, however, are largely unexplored. To better understand these processes, we investigated longline catch rates of yellowfin tuna and their distributions in the western Indian Ocean in relation to IOD events, sea surface water temperatures (SST) and estimates of net primary productivity (NPP). Catch per unit effort (CPUE) was observed to be negatively correlated to the IOD with a periodicity centred around 4 years. During positive IOD events, SSTs were relatively higher, NPP was lower, CPUE decreased and catch distributions were restricted to the northern and western margins of the western Indian Ocean. During negative IOD events, lower SSTs and higher NPP were associated with increasing CPUE, particularly in the Arabian Sea and seas surrounding Madagascar, and catches expanded into central regions of the western Indian Ocean. These findings provide preliminary insights into some of the key environmental features driving the distribution of yellowfin tuna in the western Indian Ocean and associated variability in fisheries catches. 相似文献
90.
Climate change in the 21st century simulated by HadGEM2-AO under representative concentration pathways 总被引:2,自引:0,他引:2
Hee-Jeong Baek Johan Lee Hyo-Shin Lee Yu-Kyung Hyun ChunHo Cho Won-Tae Kwon Charline Marzin Sun-Yeong Gan Min-Ji Kim Da-Hee Choi Jonghwa Lee Jaeho Lee Kyung-On Boo Hyun-Suk Kang Young-Hwa Byun 《Asia-Pacific Journal of Atmospheric Sciences》2013,49(5):603-618
We present climate responses of Representative Concentration Pathways (RCPs) using the coupled climate model HadGEM2-AO for the Coupled Model Intercomparison Project phase 5 (CMIP5). The RCPs are selected as standard scenarios for the IPCC Fifth Assessment Report and these scenarios include time paths for emissions and concentrations of greenhouse gas and aerosols and land-use/land cover. The global average warming and precipitation increases for the last 20 years of the 21st century relative to the period 1986-2005 are +1.1°C/+2.1% for RCP2.6, +2.4°C/+4.0% for RCP4.5, +2.5°C/+3.3% for RCP6.0 and +4.1°C/+4.6% for RCP8.5, respectively. The climate response on RCP 2.6 scenario meets the UN Copenhagen Accord to limit global warming within two degrees at the end of 21st century, the mitigation effect is about 3°C between RCP2.6 and RCP8.5. The projected precipitation changes over the 21st century are expected to increase in tropical regions and at high latitudes, and decrease in subtropical regions associated with projected poleward expansions of the Hadley cell. Total soil moisture change is projected to decrease in northern hemisphere high latitudes and increase in central Africa and Asia whereas near-surface soil moisture tends to decrease in most areas according to the warming and evaporation increase. The trend and magnitude of future climate extremes are also projected to increase in proportion to radiative forcing of RCPs. For RCP 8.5, at the end of the summer season the Arctic is projected to be free of sea ice. 相似文献