Bioremediation in Fractured Rock: 2. Mobilization of Chloroethene Compounds from the Rock Matrix          下载免费PDF全文

Allen M. Shapiro  Claire R. Tiedeman  Thomas E. Imbrigiotta  Daniel J. Goode  Paul A. Hsieh  Pierre J. Lacombe  Mary F. DeFlaun  Scott R. Drew  Gary P. Curtis 《Ground water》2018,56(2):317-336

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Hydrogeomorphological differentiation between floodplains and terraces          下载免费PDF全文

Qina Yan  Toshiki Iwasaki  Andrew Stumpf  Patrick Belmont  Gary Parker  Praveen Kumar 《地球表面变化过程与地形》2018,43(1):218-228

Floodplains and terraces in river valleys play important roles in the transport dynamics of water and sediment. While flat areas in river valleys can be identified from LiDAR data, directly characterizing them as either floodplain or terraces is not yet possible. To address this challenge, we hypothesize that, since geomorphic features are strongly coupled to hydrological and hydraulic dynamics and their associated variability, there exists a return frequency, or possibly a narrow band of return frequencies, of flow that is associated with floodplain formation; and this association can provide a distinctive signature for distinguishing them from terraces. Based on this hypothesis we develop a novel approach for distinguishing between floodplains and terraces that involves transforming the transverse cross‐sectional geometry of a river valley into a curve, named a river valley hypsometric (RVH) curve, and linking hydraulic inundation frequency with the features of this curve. Our approach establishes that the demarcation between floodplains and terraces can be established from the structure of steps and risers in the RVH curves which can be obtained from the DEM data. Further, it shows that these transitions may themselves be shaped by floods with 10‐ to 100‐year recurrence. We additionally show that, when floodplain width and height (above channel bottom) are normalized by bankfull width and depth, the ratio lies in a narrow range independent of the scale of the river valley. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

Effect of Catch‐Can Spacing on Calculation of Sprinkler Irrigation Application Uniformity          下载免费PDF全文

Lin Zhang  Gary P. Merkley  Pute Wu  Delan Zhu 《洁净——土壤、空气、水》2018,46(7)

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Effects of sand content on initial gravel motion in gravel‐bed rivers          下载免费PDF全文

Hiroshi Miwa  Gary Parker 《地球表面变化过程与地形》2017,42(9):1355-1364

When fine sediments are present in gravel streambeds (gravel‐framework beds), the gravel can be more easily removed from its original position, compared with gravel in a streambed without fine sediment but otherwise under the same hydraulic conditions. In this study, the effect of the presence of sand on the initiation of gravel motion in gravel riverbeds was investigated using flume experiments. The relationship between the critical Shields stress for gravel motion initiation and the fraction of sand in the bed was determined experimentally. The results can be summarized as follows. (1) When the fraction of sand in the bed is smaller than about 0.4, the critical Shields stress for the initiation of gravel motion decreases with increasing fraction of sand. The critical Shields stress increases, however, with increasing fraction of sand when it is larger than about 0.4. (2) The difference between the value of the critical Shields stress predicted by the Egiazaroff equation and the value obtained from the experimental data becomes maximum at about 0.4 of the fraction of sand. Here an empirical relation between the critical Shields stress and the fraction of sand is proposed so as to consider the effects of the ratio of the characteristic gravel size to the mean size of the bed material on the critical Shields stress. (3) Gravel in armored beds can be more easily mobilized by supplying sand as part of a sediment augmentation scheme. The sand fraction in the subsurface layer of the bed appears to reduce the friction angle of exposed particles. Sediment augmentation using sand has been recently demonstrated to be a viable alternative for mobilizing gravel for the restoration of gravel‐bed rivers downstream of dams. The quantitative evaluation obtained through the experiments reported here may be useful for the design of augmentation schemes. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

Connectivity as an emergent property of geomorphic systems     

Ellen Wohl  Gary Brierley  Daniel Cadol  Tom J. Coulthard  Tim Covino  Kirstie A. Fryirs  Gordon Grant  Robert G. Hilton  Stuart N. Lane  Francis J. Magilligan  Kimberly M. Meitzen  Paola Passalacqua  Ronald E. Poeppl  Sara L. Rathburn  Leonard S. Sklar 《地球表面变化过程与地形》2019,44(1):4-26

Connectivity describes the efficiency of material transfer between geomorphic system components such as hillslopes and rivers or longitudinal segments within a river network. Representations of geomorphic systems as networks should recognize that the compartments, links, and nodes exhibit connectivity at differing scales. The historical underpinnings of connectivity in geomorphology involve management of geomorphic systems and observations linking surface processes to landform dynamics. Current work in geomorphic connectivity emphasizes hydrological, sediment, or landscape connectivity. Signatures of connectivity can be detected using diverse indicators that vary from contemporary processes to stratigraphic records or a spatial metric such as sediment yield that encompasses geomorphic processes operating over diverse time and space scales. One approach to measuring connectivity is to determine the fundamental temporal and spatial scales for the phenomenon of interest and to make measurements at a sufficiently large multiple of the fundamental scales to capture reliably a representative sample. Another approach seeks to characterize how connectivity varies with scale, by applying the same metric over a wide range of scales or using statistical measures that characterize the frequency distributions of connectivity across scales. Identifying and measuring connectivity is useful in basic and applied geomorphic research and we explore the implications of connectivity for river management. Common themes and ideas that merit further research include; increased understanding of the importance of capturing landscape heterogeneity and connectivity patterns; the potential to use graph and network theory metrics in analyzing connectivity; the need to understand which metrics best represent the physical system and its connectivity pathways, and to apply these metrics to the validation of numerical models; and the need to recognize the importance of low levels of connectivity in some situations. We emphasize the value in evaluating boundaries between components of geomorphic systems as transition zones and examining the fluxes across them to understand landscape functioning. © 2018 John Wiley & Sons, Ltd.  相似文献   

Mapping valley bottom confinement at the network scale     

Gary R. O'Brien  Joseph M. Wheaton  Kirstie Fryirs  William W. Macfarlane  Gary Brierley  Kelly Whitehead  Jordan Gilbert  Carol Volk 《地球表面变化过程与地形》2019,44(9):1828-1845

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A 57 Ma Pacific plate palaeomagnetic pole determined from a skewness analysis of crossings of marine magnetic anomaly 25r     

Katerina E. Petronotis  Richard G. Gordon †  Gary D. Acton 《Geophysical Journal International》1994,118(3):529-554

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Evidence for relative sea-level falls during deposition of the Upper Carboniferous Millstone Grit,South Wales     

Gary J. Hampson 《Geological Journal》1998,33(4):243-266

Detailed sedimentological facies analysis of the fluvio-deltaic Millstone Grit succession (Upper Carboniferous) of South Wales reveals that a number of cyclothems bounded by marine flooding surfaces (marine bands) in these strata exhibit facies architectures that represent erosion, non-deposition and/or deposition during periods of falling relative sea-level. A major fluvial complex below the Subcrenatum Marine Band, the Farewell Rock, lies within an incised valley, with a regional unconformity (sequence boundary) at its base. This unconformity is marked by deep erosional relief, an identifiable time gap and an angular discordance in bedding. The Cumbriense Quartzite, a correlative unit containing several mature palaeosols, records a depositional hiatus on a terrace-like interfluve that lay beyond the margins of the coeval Farewell Rock valley. Cyclothems in the underlying Middle Shales contain additional surfaces and units of subtler character. Beneath the Cancellatum Marine Band, a thin (15 cm), calcareous siltstone bed (the ‘Amroth Granule Bed’) that directly overlies prodelta shales contains reworked bioclasts, bored phosphorite clasts and quartz granules. Quartz granules in this bed are interpreted to represent relict lowstand, fluviatile? deposits, which were reworked during later transgression. Three further cyclothems contain sharp-based, storm-reworked mouth bars that record an abrupt lowering of wave base, most probably during periods of falling relative sea-level. One of these cyclothems also contains a distributary channel complex, which records an abrupt influx of coarse-grained sediment of ambiguous origin. The significance of these subtle surfaces and units for intracyclothem stratigraphy has rarely been considered; their prevalence in the Middle Shales provides evidence for numerous, high-frequency relative sea-level falls, which were previously unrecognized. These relative sea-level falls appear to alternate coherently with the widespread sea-level rises recorded by the marine bands, suggesting that glacio-eustasy is their most likely driving mechanism. The notion of glacio-eustatic sea-level falls is supported by the correlation of the basal Farewell Rock sequence boundary with sequence boundaries documented in adjacent basins. The angular unconformity and a change in sediment provenance at the base of the Farewell Rock, however, suggest an additional tectonic control on stratigraphic architecture here, namely a short-lived phase of rifting or inversion prior to widespread fluvial incision. Copyright © 1998 John Wiley & Sons, Ltd.  相似文献   

Biodiversity Conservation in the REDD   总被引：1，自引：0，他引：1  

Gary D Paoli  Philip L Wells  Erik Meijaard  Matthew J Struebig  Andrew J Marshall  Krystof Obidzinski  Aseng Tan  Andjar Rafiastanto  Betsy Yaap  JW Ferry Slik  Alexandra Morel  Balu Perumal  Niels Wielaard  Simon Husson  Laura D'Arcy 《Carbon balance and management》2010,5(1):1-9

Background

Forests occur across diverse biomes, each of which shows a specific composition of plant communities associated with the particular climate regimes. Predicted future climate change will have impacts on the vulnerability and productivity of forests; in some regions higher temperatures will extend the growing season and thus improve forest productivity, while changed annual precipitation patterns may show disadvantageous effects in areas, where water availability is restricted. While adaptation of forests to predicted future climate scenarios has been intensively studied, less attention was paid to mitigation strategies such as the introduction of tree species well adapted to changing environmental conditions.

Results

We simulated the development of managed forest ecosystems in Germany for the time period between 2000 and 2100 under different forest management regimes and climate change scenarios. The management regimes reflect different rotation periods, harvesting intensities and species selection for reforestations. The climate change scenarios were taken from the IPCC's Special Report on Emission Scenarios (SRES). We used the scenarios A1B (rapid and successful economic development) and B1 (high level of environmental and social consciousness combined with a globally coherent approach to a more sustainable development). Our results indicate that the effects of different climate change scenarios on the future productivity and species composition of German forests are minor compared to the effects of forest management.

Conclusions

The inherent natural adaptive capacity of forest ecosystems to changing environmental conditions is limited by the long life time of trees. Planting of adapted species and forest management will reduce the impact of predicted future climate change on forests.  相似文献   

Vanishing river: Landscapes and lives of the Lower Verde Valley,the Lower Verde Archaeological Project     

Gary Huckleberry 《Geoarchaeology》2000,15(1):85-88

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