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41.
Mark P. S. Krekeler Pete Probst Misha Samsonov Cynthia M. Tselepis William Bates Lance E. Kearns J. Barry Maynard 《Environmental Geology》2007,53(4):709-726
Subsurface flow constructed wetlands in the village of Akumal, Quintana Roo, Mexico were surveyed to determine the general
status of the wetland systems and provide baseline information for long term monitoring and further study. Twenty subsurface
flow wetlands were surveyed and common problems observed in the systems were overloading, poor plant cover, odor, and no secondary
containment. Bulk mineral composition of aggregate from two subsurface flow constructed wetlands was determined to consist
solely of calcite using bulk powder X-ray diffraction. Some soil structure is developed in the aggregate and aggregate levels
in wetlands drop at an estimated rate between 3 and 10 cm/year for overloaded wetlands owing to dissolution. Mineral composition
from fresh aggregate samples commonly is a mixture of calcite and aragonite. Trace amounts of Pb, Zn, Co, and Cr were observed
in fresh aggregate. Coefficients of permeability (k) varied from 0.006 to 0.027 cm/s with an average values being 0.016 cm/s. Grain size analysis of fresh aggregate samples
indicates there are unimodal and multimodal size distributions in the samples with modes in the coarse and fine sand being
common. Investigations of other geologic media from the Reforma region indicate that a dolomite with minor amounts of Fe-oxide
and palygorskite is abundant and may be a better aggregate source that the current materials used. A Ca-montmorillonite bed
was identified in the Reforma region as well and this unit is suitable to serve as a clay liner to prevent leaks for new and
existing wetland systems. These newly discovered geologic resources should aid in the improvement of subsurface flow constructed
wetlands in the region. Although problems do exist in these wetlands with respect to design, these systems represent a successful
implementation of constructed wetlands at a community level in developing regions. 相似文献
42.
B.N. Maehlum K. Måseide K. Aarsnes A. Egeland B. Grandal J. Holtet T.A. Jacobsen N.C. Maynard F. Søraas J. Stadsnes E.V. Thrane J. Trøim 《Planetary and Space Science》1980,28(3):259-278
A “mother-daughter” rocket was launched from Andøya, Norway, February 1 1976 over two auroral structures. The “daughter” payload carried a 10keV electron accelerator and the “mother” carried a series of diagnostic instruments for monitoring optical and wave effects generated through beam-atmospheric interactions and production of secondary electrons.The experimental details are presented in this paper together with a survey of some of the results. This paper is also intended as a reference for a series of accompanying papers. 相似文献
43.
44.
This paper evaluates current knowledge of Laurentide eskers in Canada in the light of developments in glacier hydrology and glacial sedimentology. Questions regarding the morpho-sedimentary relations of eskers, the synchroneity and operation of R-channel systems, the role of supraglacial meltwater input and proglacial water bodies, the controls on esker pattern, and the glaciodynamic condition of the ice sheet at the time of esker formation are discussed. A morphologic classification of eskers is proposed. Five types of eskers are identified and investigated. Type I eskers likely formed in extensive, synchronous, dendritic R-channel networks under regionally stagnant ice that terminated in standing water. Type II eskers likely formed in short, subaqueously terminating R-channels or reentrants close to an ice front or grounding line that may have actively retreated during esker sedimentation. Type III eskers plausibly formed in short R-channels that drained either to interior lakes in, or tunnel channels under, regionally stagnant ice. Type IV eskers may have formed as time-transgressive segments in short, subaerially terminating R-channels (or reentrants) that developed close to the ice margin as the ice front underwent stagnation-zone retreat or downwasted and backwasted regionally (stagnant ice); however, formation in synchronous R-channels cannot be discounted on the basis of reported observations. Type V eskers may have formed in H-channels that terminated subaerially. The spatial distribution of these esker types is discussed. The factors that determined Laurentide R-channel pattern and operation were likely a complex combination of (i) supraglacial meltwater discharge, (ii) the number and location of sink holes, (iii) the ice surface slope, thickness and velocity, and (iv) the permeability, topography and rigidity of the bed. These factors cause and respond to changes in ice dynamics and thermal regime over the glacial cycle. 相似文献
45.
Benjamin M. C. Fischer Michael Rinderer Philipp Schneider Tracy Ewen Jan Seibert 《水文研究》2015,29(26):5321-5336
Mountainous headwaters consist of different landscape units including forests, meadows and wetlands. In these headwaters it is unclear which landscape units contribute what percentage to baseflow. In this study, we analysed spatiotemporal differences in baseflow isotope and hydrochemistry to identify catchment‐scale runoff contribution. Three baseflow snapshot sampling campaigns were performed in the Swiss pre‐alpine headwater catchment of the Zwäckentobel (4.25 km2) and six of its adjacent subcatchments. The spatial and temporal variability of δ2H, Ca, DOC, AT, pH, SO4, Mg and H4SiO4 of streamflow, groundwater and spring water samples was analysed and related to catchment area and wetland percentage using bivariate and multivariate methods. Our study found that in the six subcatchments, with variable arrangements of landscape units, the inter‐ and intra catchment variability of isotopic and hydrochemical compositions was small and generally not significant. Stream samples were distinctly different from shallow groundwater. An upper spring zone located near the water divide above 1,400 m and a larger wetland were identified by their distinct spatial isotopic and hydrochemical composition. The upstream wetland percentage was not correlated to the hydrochemical streamflow composition, suggesting that wetlands were less connected and act as passive features with a negligible contribution to baseflow runoff. The isotopic and hydrochemical composition of baseflow changed slightly from the upper spring zone towards the subcatchment outlets and corresponded to the signature of deep groundwater. Our results confirm the need and benefits of spatially distributed snapshot sampling to derive process understanding of heterogeneous headwaters during baseflow. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
46.
Laura L. Brothers Joseph T. Kelley Daniel F. Belknap Walter A. Barnhardt Brian D. Andrews Melissa Landon Maynard 《Geo-Marine Letters》2011,31(4):237-248
Mechanisms and timescales responsible for pockmark formation and maintenance remain uncertain, especially in areas lacking
extensive thermogenic fluid deposits (e.g., previously glaciated estuaries). This study characterizes seafloor activity in
the Belfast Bay, Maine nearshore pockmark field using (1) three swath bathymetry datasets collected between 1999 and 2008,
complemented by analyses of shallow box-core samples for radionuclide activity and undrained shear strength, and (2) historical
bathymetric data (report and smooth sheets from 1872, 1947, 1948). In addition, because repeat swath bathymetry surveys are
an emerging data source, we present a selected literature review of recent studies using such datasets for seafloor change
analysis. This study is the first to apply the method to a pockmark field, and characterizes macro-scale (>5 m) evolution
of tens of square kilometers of highly irregular seafloor. Presence/absence analysis yielded no change in pockmark frequency
or distribution over a 9-year period (1999–2008). In that time pockmarks did not detectably enlarge, truncate, elongate, or
combine. Historical data indicate that pockmark chains already existed in the 19th century. Despite the lack of macroscopic
changes in the field, near-bed undrained shear-strength values of less than 7 kPa and scattered downcore 137Cs signatures indicate a highly disturbed setting. Integrating these findings with independent geophysical and geochemical
observations made in the pockmark field, it can be concluded that (1) large-scale sediment resuspension and dispersion related
to pockmark formation and failure do not occur frequently within this field, and (2) pockmarks can persevere in a dynamic
estuarine setting that exhibits minimal modern fluid venting. Although pockmarks are conventionally thought to be long-lived
features maintained by a combination of fluid venting and minimal sediment accumulation, this suggests that other mechanisms
may be equally active in maintaining such irregular seafloor morphology. One such mechanism could be upwelling within pockmarks
induced by near-bed currents. 相似文献
47.
D. Rees T.J. Fuller-Rowell M.F. Smith R. Gordon T.L. Killeen P.B. Hays N.W. Spencer L. Wharton N.C. Maynard 《Planetary and Space Science》1985,33(4):425-456
One of the most consistent and often dramatic interactions between the high latitude ionosphere and the thermosphere occurs in the vicinity of the auroral oval in the afternoon and evening period. Ionospheric ions, convected sunward by the influence of the magnetospheric electric field, create a sunward jet-stream in the thermosphere, where wind speeds of up to 1 km s?1 can occur. This jet-stream is nearly always present in the middle and upper thermosphere (above 200 km altitude), even during periods of very low geomagnetic activity. However, the magnitude of the winds in the jet-stream, as well as its location and range in latitude, each depend on geomagnetic activity. On two occasions, jet-streams of extreme magnitude have been studied using simultaneous ground-based and satellite observations, probing both the latitudinal structure and the local time dependence. The observations have then been evaluated with the aid of simulations using a global, three-dimensional, time-dependent model of thermospheric dynamics including the effects of magnetospheric convection and particle precipitation. The extreme events, where sunward winds of above 800 ms?1 are generated at relatively low geomagnetic latitudes (60–70°) require a greatly expanded auroral oval and large cross-polar cap electric field ( ~ 150 kV). These in turn are generated by a persistent strong Interplanetary Magnetic Field, with a large southward component. Global indices such as Kp are a relatively poor indicator of the magnitude and extent of the jet-stream winds. 相似文献
48.
Processing U ores in the JEB Mill of the McClean Lake Operation in northern Saskatchewan produces spent leaching solutions (raffinates) with pH 1.5, and As and Ni concentrations up to 6800 and 5200 mg L−1, respectively. Bench-scale neutralization experiments (pH 2–8) were performed to help optimize the design of mill processes for reducing As and Ni concentrations in tailings and raffinates to 1 mg L−1 prior to their disposal. Precipitate mineralogy determined by chemical analysis, XRD, SEM, EM, XM and EXAFS methods, included gypsum (the dominant precipitate), poorly crystalline scorodite (precipitated esp. from pH 2–4), annabergite, hydrobasaluminite, ferrihydrite, green rust II and theophrastite. The As was mostly in scorodite with smaller amounts in annabergite and trace As adsorbed and/or co-precipitated, probably by ferrihydrite. Geochemical modeling indicated that above pH 2, the ion activity product (IAP) of scorodite lies between the solubility products of amorphous and crystalline phases (log Ksp = −23.0 and −25.83, respectively). The IAP decreases with increasing pH, suggesting that the crystallinity of the scorodite increases with pH. Forward geochemical models support the assumption that during neutralization, particles of added base produce sharp local pH gradients and disequilibrium with bulk solutions, facilitating annabergite and theophrastite precipitation. 相似文献
49.
Tracy L. Kijewski-Correa Andrew B. Kennedy Alexandros A. Taflanidis David O. Prevatt 《Natural Hazards》2018,93(2):627-659
The old potable water network in Byblos city is provided mainly from Ibrahim River nearby. Located in a seismic region, the aging network needs to tolerate seismic threats; thus, damage to the potable water network needs to be assessed. Therefore, first, enhancing infrastructure resilience is briefly discussed, noting briefly the need to bridge specifically between heritage risk management and engineering. Second, Byblos potable water network, seismicity, and geology are detailed. Third, the potable water network damage assessment methodology is presented. It encompasses hazard assessment, network inventory, damage functions, and model development. Data and maps are prepared using the Geographic Information System and then modeled in Ergo platform to obtain the damage to buried pipelines in the event of likely earthquake scenarios. Ergo is updated to consider recommended ground motion prediction equations (GMPEs) for the Middle East region, to consider amplification of the peak ground velocity in hazard maps due to different soil types, and to consider adequate fragility functions. Moreover, different Byblos geotechnical maps, landslide hazard, and liquefaction are investigated and embedded. Damage results to pipelines are dependent on the hazard maps obtained using different GMPEs and geotechnical maps. Asbestos cement pipelines will be most damaged, followed by polyethylene and then by ductile iron. Finally, recommendations are offered to consider an improved sustainable rehabilitation solution. The study provides a better understanding of Byblos potable water network and allows the establishment of a sustainable and resilience-to-earthquake preparedness strategy and recovery plan. 相似文献
50.
This paper addresses the treatment of the rotation of the internal components of the triple friction pendulum (TFP) isolation bearing in a numerical model previously presented by the authors. The numerical model is based on the kinematic behavior of the individual sliding surfaces and the constitutive relationships between them. The modification suggested in this paper improves the performance of the model so that the results exactly match that of the one‐dimensional piecewise linear behavior previously derived for the TFP bearing for restricted properties. The improved numerical model simulates bidirectional shear response and places no a priori restrictions on the bearing properties. The modification is put in the form of a technical communication so that the notation used and the basis of the correction could be presented with adequate clarity and so that an example of the benefit of the correction could be presented. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献