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241.
242.
Bioremediation in Fractured Rock: 1. Modeling to Inform Design,Monitoring, and Expectations
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Claire R. Tiedeman Allen M. Shapiro Paul A. Hsieh Thomas E. Imbrigiotta Daniel J. Goode Pierre J. Lacombe Mary F. DeFlaun Scott R. Drew Carole D. Johnson John H. Williams Gary P. Curtis 《Ground water》2018,56(2):300-316
Field characterization of a trichloroethene (TCE) source area in fractured mudstones produced a detailed understanding of the geology, contaminant distribution in fractures and the rock matrix, and hydraulic and transport properties. Groundwater flow and chemical transport modeling that synthesized the field characterization information proved critical for designing bioremediation of the source area. The planned bioremediation involved injecting emulsified vegetable oil and bacteria to enhance the naturally occurring biodegradation of TCE. The flow and transport modeling showed that injection will spread amendments widely over a zone of lower‐permeability fractures, with long residence times expected because of small velocities after injection and sorption of emulsified vegetable oil onto solids. Amendments transported out of this zone will be diluted by groundwater flux from other areas, limiting bioremediation effectiveness downgradient. At nearby pumping wells, further dilution is expected to make bioremediation effects undetectable in the pumped water. The results emphasize that in fracture‐dominated flow regimes, the extent of injected amendments cannot be conceptualized using simple homogeneous models of groundwater flow commonly adopted to design injections in unconsolidated porous media (e.g., radial diverging or dipole flow regimes). Instead, it is important to synthesize site characterization information using a groundwater flow model that includes discrete features representing high‐ and low‐permeability fractures. This type of model accounts for the highly heterogeneous hydraulic conductivity and groundwater fluxes in fractured‐rock aquifers, and facilitates designing injection strategies that target specific volumes of the aquifer and maximize the distribution of amendments over these volumes. 相似文献
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Erosion of hard‐rock coastal cliffs is understood to be caused by a combination of both marine and sub‐aerial processes. Beach morphology, tidal elevation and significant wave heights, especially under extreme storm conditions, can lead to variability in wave energy flux to the cliff‐toe. Wave and water level measurements in the nearshore under energetic conditions are difficult to obtain and in situ observations are rare. Here we use monthly cliff‐face volume changes detected using terrestrial laser scanning alongside beach morphological changes and modelled nearshore hydrodynamics to examine how exposed cliffs respond to changes in extreme wave conditions and beach morphology. The measurements cover the North Atlantic storms of 2013 to 2014 and consider two exposed stretches of coastline (Porthleven and Godrevy, UK) with contrasting beach morphology fronting the cliffs; a flat dissipative sandy beach at Godrevy and a steep reflective gravel beach at Porthleven. Beach slope and the elevation of the beach–cliff junction were found to influence the frequency of cliff inundation and the power of wave–cliff impacts. Numerical modelling (XBeach‐G) showed that under highly energetic wave conditions, i.e. those that occurred in the North Atlantic during winter 2013–2014, with Hs = 5.5 m (dissipative site) and 8 m (reflective site), the combination of greater wave height and steeper beach at the reflective site led to amplified wave run‐up, subjecting these cliffs to waves over four times as powerful as those impacting the cliffs at the dissipative site (39 kWm‐1 compared with 9 kWm‐1). This study highlighted the sensitivity of cliff erosion to extreme wave conditions, where the majority (over 90% of the annual value) of cliff‐face erosion ensued during the winter. The significance of these short‐term erosion rates in the context of long‐term retreat illustrates the importance of incorporating short‐term beach and wave dynamics into geomorphological studies of coastal cliff change. © 2017 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd. 相似文献
245.
Claire Carlier Stefanie B. Wirth Fabien Cochand Daniel Hunkeler Philip Brunner 《Ground water》2019,57(1):48-62
This study investigates how catchment properties influence low-flow dynamics. With 496 synthetic models composed of a bedrock and an alluvial aquifer, we systematically assess the impact of the hydraulic conductivity of both lithologies, of the hillslope and of the river slope on catchment dynamics. The physically based hydrogeological simulator HydroGeoSphere is employed, which allows obtaining a range of low-flow indicators. The hydraulic conductivity of the bedrock Kbedrock, a proxy for transmissivity, is the only catchment property exerting an overall control on low flows and explains 60% of the variance of Q95/Q50. The difference in dynamics of catchments with same Kbedrock depends on hillslope gradients and the alluvial aquifer properties. The buffering capacity of the bedrock is mainly related to Kbedrock and the hillslope gradient. We thus propose the dimensionless bedrock productivity index (BPI) that combines these characteristics with the mean net precipitation. For bedrock only models, the BPI explains 82% of the variance of the ratio of Q95 to mean net precipitation. The alluvial aquifer can significantly influence low flows when the bedrock productivity is limited. Although our synthetic catchment setup is simple, it is far more complex than the available analytical approaches or conceptual hydrological models. The direct application of the results to existing catchments requires nevertheless careful consideration of the local geological topographic and climatic conditions. This study provides quantitative insight into the complex interrelations between geology, topography and low-flow dynamics and challenges previous studies which neglect or oversimplify geological characteristics in the assessment of low flows. 相似文献
246.
One of the key issues associated with the hypothesis of catastrophic subglacial drainage of the Livingstone Lake event is whether flows of such large magnitudes are physically feasible. To explore this issue, a one‐dimensional hydraulic network flow model was developed to investigate the range of peak discharges and associated flow parameters that may have been carried by a tunnel channel network in south‐east Alberta, Canada. This tunnel channel network has been interpreted elsewhere to carry large discharges associated with subglacial meltwater flows because of the convex longitudinal profiles of individual channels. This computational modelling effort draws upon established and verified engineering principles and methods in its application to the hydraulics of this problem. Consequently, it represents a unique and independent approach to investigating the subglacial meltwater hypothesis. Based on the modelling results, it was determined that energy losses resulting from friction limit the maximum peak discharge that can be transported through the tunnel channel network to 107 m3 s−1, which is in reasonable agreement with previous estimates of flood discharges for proposed megafloods. Results show that flow through channels with convex longitudinal profiles occurs when hydraulic head exceeds 910 m (Lost River) and 950 m (Sage Creek) , respectively. These are considerably below the maximum head capable of driving flow through the system of 1360 m, beyond which ice is decoupled from the bed across the pre‐glacial drainage divide. Therefore, it is concluded that these model results support the hypothesis of catastrophic subglacial drainage during the Livingstone Lake event. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
247.
James F. J. Bryson Claire I. O. Nichols Conall Mac Niocaill 《Meteoritics & planetary science》2024,59(5):1194-1215
One key feature of our protoplanetary disk that shaped its transformation into a system of planetary bodies was its vast magnetic field. Unique constraints on the properties of this field can be gleaned from paleomagnetic measurements of certain meteorites. Here, we apply this approach to the recent CM chondrite fall Winchcombe with the aim of constructing the most complete and reliable record to date of the behavior of the disk field in the outer solar system. We find that the interior of Winchcombe carries a stable, pre-terrestrial magnetization that likely dates from the period of aqueous alteration of the CM chondrite parent body. This remanence corresponds to a paleointensity of 31 ± 17 μT accounting for the average effect of parent body rotation. Winchcombe is rich in framboids and plaquettes of magnetite, which formed via precipitation following the dissolution of iron sulfide. This contrasts with most other CM chondrites, where magnetite formed predominantly via pseudomorphic replacement of FeNi metal. Accounting for the potential differences in recording fidelities of these types of magnetite, we find that the reported paleointensities from all CM chondrites to date are likely underestimates of the disk field intensity in the outer solar system, and use our measurements to calculate a unified intensity estimate of ~78 μT. This paleointensity is consistent with two independent values from recent studies, which collectively argue that the disk field could have played a larger role in shaping the behavior of the disk in the outer solar system than previously considered. 相似文献
248.
Andrew Morton Claire Hallsworth Dominic Strogen Andrew Whitham Mark Fanning 《Marine and Petroleum Geology》2009
An integrated provenance study using provenance-sensitive heavy mineral ratios, mineral chemistry and U/Pb dating of detrital zircons has revealed significant changes in sediment provenance during deposition of the Early to Middle Jurassic succession in the Heidrun Field, offshore Mid-Norway. The variations result from the interplay of two source regions, one of which was located on the Norwegian landmass and the other on the conjugate East Greenland margin. Sediment sourced from central East Greenland is distinguished by high garnet:zircon, high rutile:zircon, low chrome spinel:zircon, garnet assemblages rich in low-Ca, high-Mg varieties, and zircon populations that include an Archean group, a diverse range of Early–Middle Proterozoic grains, and an Early Paleozoic group. These features indicate derivation from a high-grade (granulite facies) metasedimentary terrain together with Archean basement and Early Paleozoic granitoids. Norwegian-sourced sandstones differ by having lower garnet:zircon and rutile:zircon, variable chrome spinel:zircon, garnet assemblages scarce in low-Ca, high-Mg varieties, and zircon populations that lack an Archean group. Derivation from the Caledonian Nappe Domain, comprising metasediments (predominantly at amphibolite facies), ophiolites and Early Paleozoic granitoids, is indicated. Initially, during deposition of the non-marine lower part of the Åre Formation (Hettangian–Sinemurian), sediment was fed from the west, but in the upper (tidally influenced) part of the Åre Formation (Sinemurian–Pliensbachian), Norwegian-sourced material appears. Greenland-derived material disappears in the subsequent Tilje Formation (Pliensbachian), with the Tilje and subsequent Ror and Ile Formations (Toarcian–Aalenian) being predominantly sourced from the east. The regional regression at the base of the Garn Formation (Bajocian) was accompanied by a switch in provenance, with Greenland-derived material replacing sediment sourced from Norway. Variations in mineralogy offer a framework for correlation on both local and sub-regional scales. 相似文献
249.
Naomi Greenwood David J. Hydes Claire Mahaffey Andrew Wither Jon Barry David B. Sivyer David J. Pearce Susan E. Hartman Olga Andres Helen E. Lees 《Ocean Dynamics》2011,61(12):2181-2199
This paper presents data for the temporal and spatial distribution of nutrients in Liverpool Bay between 2003 and 2009 and
an analysis of inputs of nutrients from the major rivers. The spatial distribution of winter nutrient concentrations are controlled
by the region of freshwater influence (ROFI) in Liverpool Bay through the mixing of riverine freshwater and Irish Sea water,
with strong linear relationships between nutrient concentration and salinity between December and February. The location of
highest spring and summer phytoplankton biomass reflects the nutrient distributions as controlled by the ROFI. Analysis of
7 years of data showed that the seasonal cycle of winter maximum nutrient concentrations in February and drawdown in April/May
is a recurrent feature of this location, with the timing of the drawdown varying by several weeks between years. A comparison
of observed nutrient concentrations in Liverpool Bay with those predicted from inputs from rivers has been presented. Nutrient
concentrations in the rivers flowing into Liverpool Bay were highly variable and there was reasonable agreement between predicted
freshwater nutrient concentrations using data from this study and riverine nutrient concentrations weighted on the basis of
river flow, although the exact nature of mixing between the rivers could not be determined. Predicted Irish Sea nutrient concentrations
in the winter were lower than those reported for the input waters of the North Atlantic, supporting findings from previous
work that nitrogen is lost through denitrification in the Irish Sea. 相似文献
250.
Claire Seard Gilbert Camoin Yusuke Yokoyama Hiroyuki Matsuzaki Nicolas Durand Edouard Bard Sophie Sepulcre Pierre Deschamps 《Marine Geology》2011,279(1-4):63-86
The widespread occurrence of microbialites in the last deglacial reef frameworks (16–6 Ka BP) implies that the accurate study of their development patterns is of prime importance to unravel the evolution of reef architecture through time and to reconstruct the reef response to sea-level variations and environmental changes.The present study is based on the sedimentological and chronological analysis (14C AMS dating) of drill cores obtained during the IODP Expedition #310 “Tahiti Sea Level” on the successive terraces which typify the modern reef slopes from Tahiti. It provides a comprehensive data base to investigate the microbialite growth patterns (i.e. growth rates and habitats), to analyze their roles in reef frameworks and to reconstruct the evolution of the reef framework architecture during sea-level rise.The last deglacial reefs from Tahiti are composed of two distinctive biological communities: (1) the coralgal communities including seven assemblages characterized by various growth forms (branching, robust branching, massive, tabular and encrusting) that form the initial frameworks and (2) the microbial communities developed in the primary cavities of those frameworks, a few meters (1.5 to 6 m) below the living coral reef surface, where they heavily encrusted the coralgal assemblages to form microbialite crusts. The dating results demonstrate the occurrence of two distinctive generations of microbialites: the “reefal microbialites” which developed a few hundred years after coralgal communities in shallow-water environments, whereas the “slope microbialites” grew a few thousands of years later in significantly deeper water conditions after the demise of coralgal communities.The development of microbialites was controlled by the volume and the shape of the primary cavities of the initial reef frameworks determined by the morphology and the packing of coral colonies. The most widespread microbialite development occurred in frameworks dominated by branching, thin encrusting, tabular and robust branching coral colonies which built loose and open frameworks typified by a high porosity (> 50%). In contrast, their growth was minimal in compact coral frameworks formed by massive and thick encrusting corals where primary cavities yielded a low porosity (~ 30%) and could not host a significant microbialite expansion. 相似文献