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排序方式： 共有72条查询结果，搜索用时 187 毫秒
1.
Detailed field sampling and analyses and laboratory-based diffusion-cell experiments were used in conjunction with 3-D reactive transport modeling (MODFLOW and MT3D99) to quantify the fate and long-term (10 ka) transport of As in the Rabbit Lake In-pit Tailings Management Facility (RLITMF), northern Saskatchewan, Canada. The RLITMF (300 m × 425 m × 90 m thick) was engineered to ensure solute transport within the RLITMF is dominated by diffusion. Concentrations of As in the tailings pore fluids ranged from 0.24 to 140 mg/L (n = 43). Arsenic speciation analyses indicate 90% of this arsenic exists as As5+. This observation is supported by pH–Eh measurements of pore fluids (n = 135). Geochemical analyses yielded a strong inverse correlation between the Fe/As molar ratio in the tailings solids and the corresponding concentration of dissolved As, which is attributed to the adsorption of As to secondary 2-line ferrihydrite present in the tailings. Diffusion-cell testing yielded values for the effective diffusion coefficient, sorption coefficient, and effective porosity of As in the tailings of 4.5 × 10−10 m2/s, 2–4 cm3/g and 0.36, respectively. Reactive transport simulations using the field and laboratory data show adsorption of As to the tailings and diffusive transport of dissolved As in the tailings should reduce the source term concentration of As to between 40% and 70% of the initial concentrations over the 10 ka simulation period. Based on these simulations, the As concentrations in the regional groundwater, 50 m down gradient of the tailings facility, should be maintained at background concentrations of 0.001 mg/L over the 10 ka period. These findings suggest the engineered in-pit disposal of U mine tailings can provide long-term protection for the local groundwater regime from As contamination. 相似文献
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Jakub T. Szmigielski S. Lee Barbour Sean K. Carey John Kurylo A. F. McClymont M. Jim Hendry 《Hydrogeology Journal》2018,26(7):2341-2356
Steelmaking-coal waste rock placed in mountain catchments in the Elk Valley, British Columbia, Canada, drain constituents of interest (CIs) to surface water downgradient of the waste rock dumps. The role of groundwater in transporting CIs in the headwaters of mountain catchments is not well understood. This study characterizes the physical hydrogeology of a portion of a 10-km2 headwater catchment (West Line Creek) downgradient of a 2.7-km2 waste rock dump placed over a natural headwater valley-bottom groundwater system. The study site was instrumented with 13 monitoring wells. Drill core samples were collected to determine subsurface lithology and geotechnical properties. The groundwater system was characterized using field testing and water-level monitoring. The valley-bottom sediments were composed of unconsolidated glacial and meltwater successions (<64 m thick) deposited as a series of cut and fill structures overlying shale bedrock. An unconfined basal alluvial aquifer located above fractured bedrock was identified as the primary conduit for groundwater flow toward Line Creek (650 m from the toe of the dump). Discharge through the basal alluvial aquifer was estimated using the geometric mean hydraulic conductivity (±1 standard deviation). These calculations suggest groundwater discharge could account for approximately 15% (ranging from 2 to 60%) of the total water discharged from the watershed. The residence time from the base of the waste rock dump to Line Creek was estimated at <3 years. The groundwater system was defined as a snowmelt (i.e., nival) regime dominated by direct recharge (percolation of precipitation) across the catchment. 相似文献
4.
This paper presents the creep behaviour of intact and remoulded specimens of fibrous peat obtained from a field site near Anzac, Alberta, Canada. The creep behaviour was investigated by means of long-term drained and undrained triaxial tests. The development of volumetric, axial, and undrained axial strain and strain rate during drained and undrained creep tests under variable stress conditions is presented. The stress – strain – strain rate (p′–ε v–\(\dot{\varepsilon }_{\text{v}}\)) relationship is found to be unique for different stress and loading durations. The p′–ε v–\(\dot{\varepsilon }_{\text{v}}\) relationship is analysed and represented by creep isotaches. The applicability of different creep models developed for normally consolidated clay is discussed and applied to define the development of creep strain in fibrous peat under varying isotropic and deviator stresses. The secondary consolidation coefficient for evaluating the volumetric strain rate of peat is found to be applicable with some limits. The drained creep behaviour of remoulded peat specimens differs from the behaviour shown by Shelby tube specimens, whereas the undrained creep behaviour in remoulded and Shelby tube specimens is similar. 相似文献
5.
P. T. Leat R. N. Thompson M. A. Morrison G. L. Hendry A. P. Dickin 《Contributions to Mineralogy and Petrology》1991,107(3):310-327
The Yampa volcanic field (late Miocene) consists of about 70 outcrops of monogenetic cinder cones, lavas, dykes, volcanic necks and hydrovolcanic pyroclastic deposits and is situated in the most northerly part of the Rio Grande rift. Contemporaneous extension in this part of the rift was small, but there is geological and geophysical evidence that, by the late Miocene, the area was underlain by hot asthenosphere convected by the Yellowstone mantle plume. The Yampa rocks are mafic and chemically diverse, including basanites, alkali basalts, potassic trachybasalts, hawaiites and shoshonites. About half the rocks bear the xenocryst suite feldspar, pyroxene, Fe–Ti oxide, amphibole, biotite. There is a tendency for xenocryst-free rocks to be the most mafic, interpreted to indicate that the xenocrysts are cognate, and represent cumulate material from fractional crystallization of the magmas in deep crustal magma chambers. The elemental and isotopic (Nd and Sr) variations can be modelled by mixing variable proportions of partial melts of local lithospheric mantle with an OIB end-member formed by partial melting of asthenosphere. The OIB end-member appears to have the elemental and isotopic composition of typical Northern Hemisphere OIB, in particular the plume-derived basanites of Loihi seamount, Hawaii. The OIB end-member at Yampa is interpreted to have been derived from mantle convected in the Yellowstone mantle plume. 相似文献
6.
This paper addresses the distribution, origin and controls upon nitrate in a 30-km2 area of the Interior Great Plains Region of southern Alberta, Canada. High concentrations of nitrate (> 100 mg l−1 NO−3-N) occurred in several isolated enclaves below the water table in brown weathered till. Nitrate concentrations of over 300 mg l−1-N were encountered in groundwater samples collected from these enclaves. Low nitrate concentrations (< 1.1 mg l−1 NO−3-N) were also encountered in the weathered till upgradient and downgradient of the nitrate enclaves. Groundwater samples collected from the underlying grey nonweathered till and bedrock had NO−3-N concentrations of < 1.1 mg l−1.
Through the application of geochemical (NO−3-N and NH+4-N) studies, environmental isotope studies (tritium), microbial analyses (nitrifiers) and laboratory experiments, it was shown that the high nitrates found in the weathered till are the result of the oxidation of ammonium present within the tills. It is postulated that this oxidation occurred during the Holocene epoch when water tables were much lower than present-day levels (5–18 m, and 2 m below ground, respectively).
Through the use of Eh measurements, the enumeration of denitrifying bacteria and laboratory experiments, the potential for denitrification was shown to exist below the present-day water table in the weathered till as well as in the nonweathered till and bedrock. Isotopic data showed that less denitrification may be occurring within the nitrate enclaves than in adjacent downgradient areas. 相似文献
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CL de Moor SJ Johnston A Brandão RA Rademeyer JP Glazer LB Furman 《African Journal of Marine Science》2015,37(3):285-311
The waters off South Africa's coastline boast a rich mix of commercially fished species. Quantitative assessments of these marine resources have developed from simple methods first applied in the 1970s, to models that encompass a wide range of methodologies. The more valuable resources have undergone regular assessments in recent decades, with frequencies closely related to the management approach employed for each fishery. Many of these assessments form the operating models used to simulation-test candidate management procedures. This paper provides a comprehensive review of the assessments of 11 of the most important fisheries resources in South Africa. Some assessments use simple biomass dynamics models, whereas others are a hybrid of age- and length-based models, each designed to model the specific characteristics of the resource and fishery concerned. Many of the assessments have been disaggregated by species/stock and/or area as related multispecies/stock/ distribution hypotheses have arisen. This paper explores the similarities and differences in the data available and the methods applied. The review indicates that, whereas the status of three of these resources cannot be estimated reliably at present, the status of six resources is considered to be reasonable to good, whereas that of abalone Haliotis midae and West Coast rock lobster Jasus lalandii remains poor. 相似文献
9.
M. A. Hendry S. J. Smartt E. D. Skillman C. J. Evans C. Trundle D. J. Lennon P. A. Crowther I. Hunter 《Monthly notices of the Royal Astronomical Society》2008,388(3):1127-1142
The blue supergiant Sher 25 is surrounded by an asymmetric, hourglass-shaped circumstellar nebula. Its structure and dynamics have been studied previously through high-resolution imaging and spectroscopy, and it appears dynamically similar to the ring structure around SN 1987A. Here, we present long-slit spectroscopy of the circumstellar nebula around Sher 25, and of the background nebula of the host cluster NGC 3603. We perform a detailed nebular abundance analysis to measure the gas-phase abundances of oxygen, nitrogen, sulphur, neon and argon. The oxygen abundance in the circumstellar nebula (12 + log O/H = 8.61 ± 0.13 dex) is similar to that in the background nebula (8.56 ± 0.07), suggesting that the composition of the host cluster is around solar. However, we confirm that the circumstellar nebula is very rich in nitrogen, with an abundance of 8.91 ± 0.15, compared to the background value of 7.47 ± 0.18. A new analysis of the stellar spectrum with the fastwind model atmosphere code suggests that the photospheric nitrogen and oxygen abundances in Sher 25 are consistent with the nebular results. While the nitrogen abundances are high, when compared to stellar evolutionary models, they do not unambiguously confirm that the star has undergone convective dredge-up during a previous red supergiant phase. We suggest that the more likely scenario is that the nebula was ejected from the star while it was in the blue supergiant phase. The star's initial mass was around 50 M⊙ , which is rather too high for it to have had a convective envelope stage as a red supergiant. Rotating stellar models that lead to mixing of core-processed material to the stellar surface during core H-burning can quantitatively match the stellar results with the nebula abundances. 相似文献
10.