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401.
The effect of increasing gravel cover on forest roads for reduced sediment delivery to stream crossings 下载免费PDF全文
Kristopher R. Brown Kevin J. McGuire W. Michael Aust W. Cully Hession C. Andrew Dolloff 《水文研究》2015,29(6):1129-1140
Direct sediment inputs from forest roads at stream crossings are a major concern for water quality and aquatic habitat. Legacy road–stream crossing approaches, or the section of road leading to the stream, may have poor water and grade control upon reopening, thus increasing the potential for negative impacts to water quality. Rainfall simulation experiments were conducted on the entire running surface area associated with six reopened stream crossing approaches in the south‐western Virginia Piedmont physiographic region, USA. Event‐based surface run‐off and associated total suspended solid (TSS) concentrations were compared among a succession of gravel surfacing treatments that represented increasing intensities of best management practice (BMP) implementation. The three treatments were no gravel (10–19% cover), low gravel (34–60% cover), and high gravel (50–99% cover). Increased field hydraulic conductivity was associated with maximized surface cover and ranged from 7.2 to 41.6, 11.9 to 46.3, and 16.0 to 58.6 mm h−1 respectively for the no gravel, low gravel, and high gravel treatments. Median TSS concentration of surface run‐off for the no gravel treatment (2.84 g l−1) was greater than low gravel (1.10 g l−1) and high gravel (0.82 g l−1) by factors of 2.6 and 3.5 respectively. Stream crossing approaches with 90–99% surface cover had TSS concentrations below 1 g l−1. Reducing the length of road segments that drain directly to the stream can reduce the costs associated with gravel surfacing. This research demonstrates that judicious and low‐cost BMPs can ameliorate poor water control and soil erosion associated with reopening legacy roads. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
402.
This special issue (SI) ‘A Tribute to Edward P. Glenn (1947-2017): A legacy of Scientific Environmental Assessment and Applications in Hydrological Processes’ is a celebration of the extensive work of Dr. Ed Glenn that was instrumental across multiple sub-disciplines of hydrology. The SI highlights four primary areas of hydrological processes that are cornerstones of Ed Glenn's over four decades of research. These contributions cover the following specialties: (i) Hydrology in the Colorado River Delta; (ii) Riparian ecosystem water use; (iii) Riparian Plant ecophysiology and ecohydrology; and (iv) Methods and models to characterize evapotranspiration. Since Ed was passionate about the dryland delta at the end of the Colorado River, we begin with four research studies that focus on this special region on the U.S.–Mexico border which encompasses four states (Baja and Sonora in Mexico and California and Arizona in United States) as well as tribal communities in the transboundary area. The Colorado River delta reaches the Northern Gulf of California in the Sea of Cortez which has been designated as a UNESCO international biosphere reserve (‘Reserva de la Biosfera El Pinacate y Gran Desierto de Altar’), which includes the Upper Gulf of California and Delta of the Colorado River (‘Reserva de la Biosfera Alto Golfo de California y Delta del Río Colorado’). Ed spent the majority of his last three decades on water balance studies and on ground-based transpiration quantification for validation of satellite and airborne remote sensing methods. We wrap up the special issue with contributions related to improving satellite and airborne remote sensing estimation of actual evapotranspiration. It is our pleasure to summarize the 16 research studies contributed to the special issue to honour Ed Glenn's research interests. 相似文献
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Precipitation data are important for hydrometeorological analyses, yet there are many ways to measure precipitation. The impact of station density analysed by the current study by comparing measurements from the Missouri Mesonet available via the Missouri Climate Center and Community Collaborative Rain, Hail, and Snow (CoCoRaHS) measurements archived at the program website. The CoCoRaHS data utilize citizen scientists to report precipitation data providing for much denser data resolution than available through the Mesonet. Although previous research has shown the reliability of CoCoRaHS data, the results here demonstrate important differences in details of the spatial and temporal distribution of annual precipitation across the state of Missouri using the two data sets. Furthermore, differences in the warm and cold season distributions are presented, some of which may be related to interannual variability such as that associated with the El Niño and Southern Oscillation. The contradictory results from two widely‐used datasets display the importance in properly choosing precipitation data that have vastly differing temporal and spatial resolutions. With significantly different yearly aggregated precipitation values, the authors stress caution in selecting 1 particular rainfall dataset as conclusions drawn could be unrepresentative of the actual values. This issue may be remediated by increased spatiotemporal coverage of precipitation data. 相似文献
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Taphonomy or signal sensitivity in palaeoecological investigations of Norse landnám in Vatnahverfi,southern Greenland? 下载免费PDF全文
Paul M. Ledger Kevin J. Edwards J. Edward Schofield 《Boreas: An International Journal of Quaternary Research》2015,44(1):197-215
Anthrosols (cf. plaggen soils) are commonly found across the homefields of Norse farms, yet the extent to which these taphonomically complex and heterogeneous deposits provide reliable archives of environmental change and vegetation history has rarely been investigated. This paper compares the palynological signature contained within an anthrosol located beside Norse farm ruins in the Eastern Settlement of Greenland, with that from a mire situated ~400 m from the nearest archaeological remains. The investigation covers a period of ~1000 years leading into, through, and beyond the Greenlandic landnám of AD 985. The results demonstrate that, as anticipated, the anthrosol contains a strong signal for human impact associated with settlement and occupation, although changes in both pollen percentages and accumulation rates (influx) through the profile appear smooth, not erratic, and radiocarbon dates are conformable. Thus the palynological signature contained in the anthrosol is broadly comparable to the patterns characteristic of stratified natural contexts (e.g. mires) with small pollen source areas that are located in close proximity to former Norse structures. Nevertheless, it is also demonstrated that secondary microfossils are a major component of the pollen assemblages within the anthrosol, and pollen influx is notably an order of magnitude higher when compared against the peat core taken from the mire. It is suggested that this may result from the addition of pollen contained in animal dung, augmenting that accumulating through the natural accretion of pollen derived from the surrounding vegetation and landing on the surface of the anthrosol. Although this complicates any palynological interpretation, by adopting a cautious approach we argue that anthrosols can be used to extract useful information about vegetation history at a local scale, as well as providing indirect evidence of landscape impacts and resource use around farmsteads. 相似文献
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Tree-ring reconstructed dry season rainfall in Guatemala 总被引:1,自引:0,他引:1
Anchukaitis Kevin J. Taylor Matthew J. Leland Caroline Pons Diego Martin-Fernandez Javier Castellanos Edwin 《Climate Dynamics》2015,45(5-6):1537-1546
Climate Dynamics - Drought in Guatemala has negative consequences for agriculture and potable water supplies, particularly in regions of the country with highly seasonal rainfall. General... 相似文献
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Robert Graves Thomas H. Jordan Scott Callaghan Ewa Deelman Edward Field Gideon Juve Carl Kesselman Philip Maechling Gaurang Mehta Kevin Milner David Okaya Patrick Small Karan Vahi 《Pure and Applied Geophysics》2011,168(3-4):367-381
CyberShake, as part of the Southern California Earthquake Center??s (SCEC) Community Modeling Environment, is developing a methodology that explicitly incorporates deterministic source and wave propagation effects within seismic hazard calculations through the use of physics-based 3D ground motion simulations. To calculate a waveform-based seismic hazard estimate for a site of interest, we begin with Uniform California Earthquake Rupture Forecast, Version 2.0 (UCERF2.0) and identify all ruptures within 200?km of the site of interest. We convert the UCERF2.0 rupture definition into multiple rupture variations with differing hypocenter locations and slip distributions, resulting in about 415,000 rupture variations per site. Strain Green Tensors are calculated for the site of interest using the SCEC Community Velocity Model, Version 4 (CVM4), and then, using reciprocity, we calculate synthetic seismograms for each rupture variation. Peak intensity measures are then extracted from these synthetics and combined with the original rupture probabilities to produce probabilistic seismic hazard curves for the site. Being explicitly site-based, CyberShake directly samples the ground motion variability at that site over many earthquake cycles (i.e., rupture scenarios) and alleviates the need for the ergodic assumption that is implicitly included in traditional empirically based calculations. Thus far, we have simulated ruptures at over 200 sites in the Los Angeles region for ground shaking periods of 2?s and longer, providing the basis for the first generation CyberShake hazard maps. Our results indicate that the combination of rupture directivity and basin response effects can lead to an increase in the hazard level for some sites, relative to that given by a conventional Ground Motion Prediction Equation (GMPE). Additionally, and perhaps more importantly, we find that the physics-based hazard results are much more sensitive to the assumed magnitude-area relations and magnitude uncertainty estimates used in the definition of the ruptures than is found in the traditional GMPE approach. This reinforces the need for continued development of a better understanding of earthquake source characterization and the constitutive relations that govern the earthquake rupture process. 相似文献