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124.
P. Byrne A. Binley A. L. Heathwaite S. Ullah C. M. Heppell K. Lansdown H. Zhang M. Trimmer P. Keenan 《水文研究》2014,28(17):4766-4779
We examined the influence of river stage on subsurface hydrology and pore water chemistry within the hyporheic zone of a groundwater‐fed river during the summer baseflow period of 2011. We found river stage and geomorphologic environment to control chemical patterns in the hyporheic zone. At a high river stage, the flux of upwelling water in the shallow sediments (>20 cm) decreased at sample sites in the upper section of our study reach and increased substantially at sites in the lower section. This differential response is attributed to the contrasting geomorphology of these subreaches that affects the rate of the rise and fall of a river stage relative to the subsurface head. At sites where streamward vertical flux decreased, concentration profiles of a conservative environmental tracer suggest surface water infiltration into the riverbed below depths recorded at a low river stage. An increase in vertical flux at sites in the lower subreach is attributed to the movement of lateral subsurface waters originating from the adjacent floodplain. This lateral‐moving water preserved or decreased the vertical extent of the hyporheic mixing zone observed at a low river stage. Downwelling surface water appeared to be responsible for elevated dissolved organic carbon (DOC) and manganese (Mn) concentrations in shallow sediments (0–20 cm); however, lateral subsurface flows were probably important for elevated concentrations of these solutes at deeper levels. Results suggest that DOC delivered to hyporheic sediments during a high river stage from surface water and lateral subsurface sources could enhance heterotrophic microbial activities. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
125.
Mehrotra Nivedita Shah Santosh K. Basavaiah Nathani Kar Ratan 《Journal of Paleolimnology》2022,68(3):297-313
Journal of Paleolimnology - The sediment deposits of northwestern Tripura, northeast India, revealed the enhanced proximity to the marginal marine environments, forest cover variations and... 相似文献
126.
Jyoti Shah Deepak C. Srivastava Vipul Rastogi Rajit Ghosh Aditi Pal 《Journal of the Geological Society of India》2010,75(1):89-97
Most of the existing methods of strain analysis can estimate strain in a single form of distorted brachiopod, or trilobite
provided independent evidence, such as the association of the fossil with cleavage and/or stretching lineation is available
for inferring the direction of maximum principal strain. This article proposes a simple computer graphics based method and
its MATLAB code that determine the minimum amount of strain in a single distorted fossil form even if data for inferring the
maximum principal strain direction are lacking. Our method is a rapid computer-graphics alternative to some of the existing
analytical methods.
In a distorted fossil form of original bilateral symmetry, the relative senses of angular shears along the hinge line and
the median line are mutually opposite to each other. It follows, therefore, that the maximum principal strain direction lies
within the acute angle between the hinge and the median lines in the plane of the fossil. Using this principle, our method
performs several simulations such that each simulation retrodeforms the distorted fossil by assuming a particular orientation,
lying within the acute angle between the hinge line and the median line, as the potential direction of the maximum principal
strain. Each simulation of retrodeformation yields a potential strain ratio. The distribution of all the potential strain
ratios, obtained by assuming different orientations as the potential directions of the maximum strain, is typically a parabola-like
curve with a distinct vertex that corresponds to the minimum amount of strain in the distorted fossil. An entirely computer
graphical approach is somewhat time-intensive because it involves a large number of retrodeformational simulations. We, therefore,
give a MATLAB code, namely, the Minstrain, that rapidly retrodeforms the fossil and determines the minimum strain with precision. 相似文献
127.
Extinction depth and evapotranspiration from ground water under selected land covers 总被引:7,自引:0,他引:7
In many landscapes, vegetation extracts water from both the unsaturated and the saturated zones. The partitioning of evapotranspiration (ET) into vadose zone evapotranspiration and ground water evapotranspiration (GWET) is complex because it depends on land cover and subsurface characteristics. Traditionally, the GWET fraction is assumed to decay with increasing depth to the water table (DTWT), attaining a value of 0 at what is termed the extinction depth. A simple assumption of linear decay with depth is often used but has never been rigorously examined using unsaturated-saturated flow simulations. Furthermore, it is not well understood how to relate extinction depths to characteristics of land cover and soil texture. In this work, variable saturation flow theory is used to simulate GWET for three land covers and a range of soil properties under drying soil conditions. For a water table within half a meter of the land surface, nearly all ET is extracted from ground water due to the close hydraulic connection between the unsaturated and the saturated zones. For deep-rooted vegetation, the decoupling of ground water and vadose zone was found to begin at water table depths between 30 and 100 cm, depending on the soil texture. The decline of ET with DTWT is better simulated by an exponential decay function than the commonly used linear decay. A comparison with field data is consistent with the findings of this study. Tables are provided to vary the extinction depth for heterogeneous landscapes with different vegetation cover and soil properties. 相似文献
128.
Pedo and biogeochemical studies of mafic and ultramfic rocks in the Mingora and Kabal areas,Swat, Pakistan 总被引:1,自引:0,他引:1
This study highlights the heavy metals (HMs) distribution in soils and their uptake by wild plants grown in the soils derived
from the mafic and ultramafic terrains. Plant and soil samples were analyzed for Cu, Pb, Zn, Cr, Ni and Cd using atomic absorption
spectrophotometer. The data indicate that almost all the HMs in the soil samples collected from the study area exceeded the
reference and normal agricultural soils. Greater variability was noticed in the uptake of HMs by various plants grown on the
studied soils. High concentrations of Cu and Zn in Cannabis sativa L. (seft hemp), Pb in Ailanthus altissima (Mill.) (Ailanto), Ni and Cr in Indigofrra gerardiana Wall. ex Baker (sage), and Saccharum griffihii Munro ex Boiss. (plume grass) were noticed among the studied plants. The multifold enrichments of Cr and Ni in the Indigofrra gerardiana and Saccharum griffihii as compared to the other plants of the study area suggested that these plants have the ability to uptake and translocate
high concentrations of Cr and Ni. The excessive concentrations of Cr and Ni in these plants can be used for mineral prospecting
but their main concern could be of serious environmental problems and health risks in the inhabitants of the study areas. 相似文献
129.
H. A. Shah W. Masood M. T. Asim M. N. S. Qureshi 《Astrophysics and Space Science》2014,350(2):615-622
In the present work, we have considered the nonlinear effects due to trapped electrons in an inhomogeneous degenerate quantum plasma. The formation of drift solitary structures has been investigated for both fully and partially degenerate plasmas. The Sagdeev potential approach has been employed to obtain arbitrary amplitude solitary structures. Interestingly, for a fixed value of density, not only compressive but rarefactive solitary structures have been obtained for a certain temperature range. Furthermore, it has been observed that the drift solitary structures exist only for the case when the drift velocity is smaller than the velocity of the nonlinear structure. The theoretical results obtained have been analyzed numerically for the parameters typically found in white dwarfs and the relevance of the results with regard to white dwarf asteroseismology is also pointed out. 相似文献
130.
The magnitude and frequency of coastal storms are expected to increase with rising global sea levels, which necessitates evaluating coastal flood adaptation measures. This study examines an important issue in the context of coastal flood protection, namely, the decision when to adopt protection measures. For any given coastal region, our benefit-cost framework allows us to determine the optimal timing of initiating protection that maximizes expected net benefits. We present an application of this framework to a coastal area in Connecticut. Our results suggest that the optimal timing of adopting protection may vary across different census blocks within the study area. We find that using a relatively low discount rate in the benefit-cost analysis implies greater heterogeneity in the timing decisions and earlier overall adoption, whereas, with higher discount rates, the timing decisions are reduced to a choice between early protection and no protection at all. If possible negative environmental and aesthetic impacts of sea barriers are taken into account, delaying protection would become more desirable, with the extent of delay being sensitive to the relative magnitude of one-time costs (e.g., loss of ocean view and recreational opportunities) vs. continuous costs (e.g., shoreline erosion and loss of wetlands). 相似文献