Effects of suspended sediment characteristics and bed sediment transport on streambed clogging     

Kristin J. Rehg  Aaron I. Packman  Jianhong Ren 《水文研究》2005,19(2):413-427

Fine sediment deposition in streambeds can reduce pore water fluxes and the overall rate of hyporheic exchange, producing deleterious effects on benthic and hyporheic ecological communities. To increase understanding of the factors that control the reduction of hyporheic exchange by fine sediment deposition, we conducted experiments in a laboratory flume to observe changes in the rates of solute exchange and kaolinite clay deposition as substantial amounts of kaolinite accumulated in the streambed. Two long‐term experiments were conducted, with durations of 14 days and 29 days. Use of a laboratory flume system allowed steady stream flow conditions to be maintained throughout both experiments, and alternating injections of known quantities of kaolinite and a sodium chloride tracer were used to assess the effect of clay accumulation on hyporheic exchange directly. In the first experiment, there was no bed sediment transport and kaolinite deposition formed a highly clogged near‐surface layer that greatly reduced hyporheic exchange. Application of a fundamental model for advective hyporheic exchange indicated that the effective permeability and porosity of the streambed decreased substantially during the course of the experiment. In the second experiment, the kaolinite was prepared with different surface properties to be more mobile, and the experiment was conducted with a small degree of bed sediment transport. As a result, no distinct clogged layer developed, and the rate of hyporheic exchange was found to remain approximately constant throughout the experiment (29 days). These results indicate that increasing fine sediment loads, e.g. those that occur from changes in land use, can have substantially different impacts on hyporheic exchange and associated ecological processes depending on the stream flow conditions, the rate and frequency of bed sediment transport, and the extent of interaction of the introduced fines with bed sediments. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

Global earthquake casualties due to secondary effects: a quantitative analysis for improving rapid loss analyses   总被引：1，自引：0，他引：1  

Kristin D. Marano  David J. Wald  Trevor I. Allen 《Natural Hazards》2010,52(2):319-328

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Physics of the Omori law: Inferences from interevent time distributions and pore pressure diffusion modeling     

Mattias Lindman  Bjrn Lund  Roland Roberts  Kristin Jonsdottir 《Tectonophysics》2006,424(3-4):209

Empirical laws and statistics of earthquakes are valuable as a basis for a better understanding of the earthquake cycle. In this paper we focus on the postseismic phase and the physics of aftershock sequences. Using interevent time distributions for a catalogue of Icelandic seismicity, we infer that the parameter C₂ in the Omori law, often considered to represent incomplete detection of aftershocks, is at least in part related to the physics of the earthquake process. We investigate the role of postseismic pore pressure diffusion after two Icelandic earthquakes on the rate of aftershocks and what we can infer about the physical meaning of C₂ from the diffusion process. Using the Mohr–Coulomb failure criterion we obtain a rate of triggered points in our diffusion model that agrees with the modified Omori law, with a value of C₂ that is consistent with data. Our pore pressure diffusion model suggests that C₂ is related to the process of reducing high pore pressure gradients existing across a fault zone at short times after a main shock.  相似文献   

Bacterial responses in activity and community composition to photo-oxidation of dissolved organic matter from soil and surface waters   总被引：1，自引：0，他引：1  

Kristin E. Judd  Byron C. Crump  George W. Kling 《Aquatic Sciences - Research Across Boundaries》2007,69(1):96-107

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Baseline study of perfluorooctane sulfonate occurrence in mussels, Mytilus galloprovincialis, from north-central Portuguese estuaries     

Cunha I  Hoff P  Van de Vijver K  Guilhermino L  Esmans E  De Coen W 《Marine pollution bulletin》2005,50(10):1128-1132

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The sense of rotation of subhaloes in cosmological dark matter haloes     

Kristin Warnick  Alexander Knebe 《Monthly notices of the Royal Astronomical Society》2006,369(3):1253-1266

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North American Earth Science Megaproject Continuum, Part 3: New Canadian EON-ROSE Program     

Katherine Boggs  David Eaton  Thomas James  Roy Hyndman  Malaika Ulmi  Pascal Audet  Ed Johnston  Michael Sideris  Ron Clowes  Julie Elliott  Jeff Freymueller  Paul Kushner  Kristin Morell  Derek Schutt  Rick Aster  Frank Vernon  Michael Hedlin  Catherine de Groot-Hedlin  Eric Donovan  Roland Stull 《《地质学报》英文版》2018,92(Z1):12-13

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Introducing top-down methods in assessing compliance with the Kyoto Protocol     

Kristin Rypdal  Frode Stordal  Jan Fuglestvedt  Terje Berntsen 《Climate Policy》2013,13(4):393-405

Abstract

The Kyoto Protocol has an ambitious reporting and review system to assess Parties' compliance with their emission commitments. It is based on a ‘bottom-up’ approach; that is, each Party is required to submit detailed inventories of emissions and removals. This requires considerable resources and may still not detect all important cases of non-compliance. We consider the case for introducing ‘top-down’ methods; that is, independent inverse modelling methods that calculate probable emissions using measured concentrations of gases in the atmosphere and meteorological models. We argue that the top-down methods are at present too inaccurate, too cumbersome, and politically too problematic to serve as independent alternatives to the reported emission inventories for assessing compliance, although they could be useful in monitoring the global success of the protocol. We conclude that these top-down approaches may supplement the traditional emission inventories, in particular those dealing with fluorinated gases, thereby providing input for improving the emission inventory methods.  相似文献   

Gas hydrate within the Winona Basin, offshore western Canada     

Michael Riedel  Kristin M.M. Rohr 《Marine and Petroleum Geology》2012,30(1):66-80

In western Canada gas hydrates have been thought to exist primarily in the Cascadia accretionary prism off southern Vancouver Island, British Columbia (BC). We present evidence for the existence of gas hydrate in folds and ridges of the Winona Basin up to 40 km seaward from the foot of the continental slope off northern Vancouver Island. The occurrence of a bottom-simulating reflector (BSR) observed in a number of vintage seismic reflection profiles is strongly correlated to faulted, and folded sedimentary ridges and buried folds. The observed tectonic structures of the Winona Basin are within the rapidly evolving Juan de Fuca - Cascadia - Queen Charlotte triple junction off BC. Re-processing of multi-channel data imaged mildly to strongly deformed sediments; the BSR is confined to sediments with stronger deformation. Changes in the amplitude character of sediment-reflections above and below the depth of the base of gas hydrate stability zone were also used as an indicator for the presence of gas hydrate. Additionally, regional amplitude and frequency reduction below some strong BSR occurrences may indicate free gas accumulations. Gas hydrate formation in the Winona Basin appears strongly constrained to folds and ridges and thus correlated to deeper-routed fluid-advection regimes. Methane production from in situ microbial activities as a source of gas to form gas hydrates, as proposed to be a major contributor for gas hydrates within the accretionary prism to the south, appears to be insufficient to produce the widespread gas hydrate occurrences in the Winona Basin. Potential reasons for the lack of sufficient in situ gas production may be that sedimentation rates are 5-100 times higher than those in the accretionary prism so that available organic carbon moves too quickly through the gas hydrate stability field. The confinement of BSRs to ridges and folds within the Winona Basin results in an areal extent of gas hydrate occurrences that is a factor of five less than what is expected from regional gas hydrate stability field mapping using water-depth (pressure) as the only controlling factor only.  相似文献   

Wood distribution in neotropical forested headwater streams of La Selva,Costa Rica     

Daniel Cadol  Ellen Wohl  Jaime R. Goode  Kristin L. Jaeger 《地球表面变化过程与地形》2009,34(9):1198-1215

Surveys of wood along 30 forested headwater stream reaches in La Selva Biological Station in north‐eastern Costa Rica represent the first systematic data reported on wood loads in neotropical streams. For streams with drainage areas of 0·1–8·5 km² and gradients of 0·2–8%, wood load ranged from 3 to 34·7 m³ wood/100 m channel and 41–612 m³ wood/ha channel. These values are within the range reported for temperate streams. The variables wood diameter/flow depth, stream power, the presence of backflooding, and channel width/depth are consistently selected as significant predictors by statistical models for wood load. These variables explain half to two‐thirds of the variability in wood load. These results, along with the spatial distribution of wood with respect to the thalweg, suggest that transport processes exert a greater influence on wood loads than recruitment processes. Wood appears to be more geomorphically effective in altering bed elevations in gravel‐bed reaches than in reaches with coarser or finer substrate. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献