Hydrologic Setting of Two Interdunal Valleys in the Central Sand Hills of Nebraska     

David C. Gosselin  Steve Drda  F. Edwin Harvey  Jim Goeke 《Ground water》1999,37(6):924-933

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Peripheral gully and landslide erosion on an extreme anthropogenic landscape produced by mountaintop removal coal mining     

Miles Reed  Steve Kite 《地球表面变化过程与地形》2020,45(9):2078-2090

Mountaintop removal/valley fill coal mining (MTR/VF) in central Appalachia has buried an estimated 4000 km of headwater streams, but the long-term geomorphic consequences of the anthropogenic valley fills and associated mined landscapes are poorly understood. These anthropogenic landscapes are not intended to be maintained in perpetuity once reclamation is complete. Here we present the first ever field-based study of erosional landforms on this type of mined landscape paired with the subsequent examination of 10 regional LiDAR (light detection and ranging) datasets for gullies and landslides in a transect from eastern Kentucky to central West Virginia. Field observations indicate that overtopping of or intentional discharge from drainage systems and overtopping of valley fill terraces can initiate gullying. We manually extracted 1328 gullies from 512 km² of mined landscape within the LiDAR datasets. Gullies are predominantly located along the perimeter of the mined landscape with the majority of gullies associated with drainage systems. The number of gullies linearly scales with mined area (R² = 0.66). We observed 387 landslides along the perimeter of MTR/VF. Within the datasets, landslides per km² ranged from 0.1 to 3.9. We observed 34 landslides within fully reclaimed valley fills, a heretofore undocumented phenomenon. Over 90% of these landslides were in Kentucky datasets, which covered only 47% of total mined area analyzed. Previously measured regional differences in the angle of friction of mine spoils or construction practices may explain the abundance of gullies and elevated level of landslide occurrence in eastern Kentucky valley fills relative to West Virginia. Observations of erosion on regionally extensive MTR/VF landscapes warrant further study to better ascertain ecological impacts. Large-scale alteration by surface mining in steep landscapes may generally lead to peripheral gully erosion. © 2020 John Wiley & Sons, Ltd.  相似文献   

Increasing non-linearity of the storage-discharge relationship in sub-Arctic catchments     

Alexa M. Hinzman  Ylva Sjöberg  Steve W. Lyon  Stefan W. Ploum  Ype van der Velde 《水文研究》2020,34(19):3894-3909

The Arctic is warming at an unprecedented rate. We hypothesis that as seasonally frozen soils thaw and recede in extent as a response to this warming, flow path diversity and thus hydrologic connectivity increases. This enhanced hydrologic connectivity then increases the non-linearity of the storage-discharge relationship in a catchment. The objective of this study is to test this hypothesis by quantifying trends and spatio-temporal differences in the degree of linearity in the storage-discharge relationships for 16 catchments within Northern Sweden from 1950 to 2018. We demonstrate a clear increase in non-linearity of the storage-discharge relationship over time for all catchments with 75% showing a statistically significant increase in non-linearity. Spring has significantly more linear storage-discharge relationships than summer for most catchments (75%) supporting the idea that seasonally frozen soils with a low degree of hydrological connectivity have a linear storage-discharge relationship. For the period considered, spring also showed greater change in storage-discharge relationship trends than summer signifying that changes in recessions are primarily occurring during the thawing period. Separate storage-discharge analyses combined with preceding winter conditions demonstrated that especially cold winters with little snow yielded springs and summers with more linear storage-discharge relationships. We show that streamflow recession analysis reflects ongoing hydrological change of an arctic landscape as well as offering new metrics for tracking change across arctic and sub-arctic landscapes.  相似文献   

Antimicrobial-resistance of Streptococcus pneumoniae isolated from the Lebanese environment   总被引：4，自引：0，他引：4  

Harakeh S  Yassine H  El-Fadel M 《Marine environmental research》2006,62(3):181-193

The aim of this study was to isolate and molecularly characterize Streptococcus pneumoniae in samples collected from the aquatic environment in Lebanon. For this purpose, 57 samples of ground waters, sea water, sediments and crabs were collected. Biochemical tests as well as PCR were used for further identification and molecular characterization of 46 suspected isolates using specific primers for the lytA-gene and protein 2B-gene. The confirmed isolates were evaluated for their antimicrobial resistance, using the minimum inhibitory concentration method. Crab samples exhibited a high contamination level of an average count of 8.2 x 10(4)CFU/g. In water samples, the highest contamination was recorded near a coastal landfill with a bacterial count of 1.8 x 10(3)CFU/ml whereas the lowest bacterial counts (non detectable) were observed in ground water samples. Twenty out of the 46 suspected isolates came from sea water, and 17 out of those were characterized by PCR as S. pneumoniae. Testing the antimicrobial resistance of the 20 isolates to various antimicrobials showed that all sea water isolates were resistant to vancomycin, gentamicin, and oxacillin (100%), whereas 62.5% were resistant to clindamycin, and only 25% were erythromycin resistant. Resistance rates were higher in the case of fresh water samples, with 57% resistance to erythromycin, and 100% resistance to vancomycin, gentamicin, clindamycin and oxacillin. Alternatively, all tested crab isolates were susceptible to erythromycin. However, they showed a high resistance of 80% against vancomycin, gentamicin, clindamycin and 100% against oxacillin.  相似文献   

The Winchcombe fireball—That lucky survivor     

Sarah McMullan  Denis Vida  Hadrien A. R. Devillepoix  Jim Rowe  Luke Daly  Ashley J. King  Martin Cupák  Robert M. Howie  Eleanor K. Sansom  Patrick Shober  Martin C. Towner  Seamus Anderson  Luke McFadden  Jana Horák  Andrew R. D. Smedley  Katherine H. Joy  Alan Shuttleworth  Francois Colas  Brigitte Zanda  Áine C. O'Brien  Ian McMullan  Clive Shaw  Adam Suttle  Martin D. Suttle  John S. Young  Peter Campbell-Burns  Richard Kacerek  Richard Bassom  Steve Bosley  Richard Fleet  Dave Jones  Mark McIntyre  Nick James  Derek Robson  Paul Dickinson  Philip A. Bland  Gareth S. Collins 《Meteoritics & planetary science》2024,59(5):927-947

On February 28, 2021, a fireball dropped ∼0.6 kg of recovered CM2 carbonaceous chondrite meteorites in South-West England near the town of Winchcombe. We reconstruct the fireball's atmospheric trajectory, light curve, fragmentation behavior, and pre-atmospheric orbit from optical records contributed by five networks. The progenitor meteoroid was three orders of magnitude less massive (∼13 kg) than any previously observed carbonaceous fall. The Winchcombe meteorite survived entry because it was exposed to a very low peak atmospheric dynamic pressure (∼0.6 MPa) due to a fortuitous combination of entry parameters, notably low velocity (13.9 km s⁻¹). A near-catastrophic fragmentation at ∼0.07 MPa points to the body's fragility. Low entry speeds which cause low peak dynamic pressures are likely necessary conditions for a small carbonaceous meteoroid to survive atmospheric entry, strongly constraining the radiant direction to the general antapex direction. Orbital integrations show that the meteoroid was injected into the near-Earth region ∼0.08 Myr ago and it never had a perihelion distance smaller than ∼0.7 AU, while other CM2 meteorites with known orbits approached the Sun closer (∼0.5 AU) and were heated to at least 100 K higher temperatures.  相似文献   

Iron oxides in comet 81P/Wild 2     

John C. BRIDGES  Mark J. BURCHELL  Hitesh C. CHANGELA  Nick J. FOSTER  J. Alan CREIGHTON  James D. CARPENTER  Steve J. GURMAN  Ian A. FRANCHI  Henner BUSEMANN 《Meteoritics & planetary science》2010,45(1):55-72

Abstract– We have used synchrotron Fe‐XANES, XRS, microRaman, and SEM‐TEM analyses of Stardust track 41 slice and track 121 terminal area slices to identify Fe oxide (magnetite‐hematite and amorphous oxide), Fe‐Ti oxide, and V‐rich chromite (Fe‐Cr‐V‐Ti‐Mn oxide) grains ranging in size from 200 nm to ～10 μm. They co‐exist with relict FeNi metal. Both Fe‐XANES and microRaman analyses suggest that the FeNi metal and magnetite (Fe₂O₃FeO) also contain some hematite (Fe₂O₃). The FeNi has been partially oxidized (probably during capture), but on the basis of our experimental work with a light‐gas gun and microRaman analyses, we believe that some of the magnetite‐hematite mixtures may have originated on Wild 2. The terminal samples from track 121 also contain traces of sulfide and Mg‐rich silicate minerals. Our results show an unequilibrated mixture of reduced and oxidized Fe‐bearing minerals in the Wild 2 samples in an analogous way to mineral assemblages seen in carbonaceous chondrites and interplanetary dust particles. The samples contain some evidence for terrestrial contamination, for example, occasional Zn‐bearing grains and amorphous Fe oxide in track 121 for which evidence of a cometary origin is lacking.  相似文献   

The solar system beyond Neptune,edited by M. A. Barucci,H. Boehnhardt,D. P. Cruikshank,and A. Morbidelli     

Steve Kortenkamp 《Meteoritics & planetary science》2009,44(3):463-464

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Entanglement of Antarctic fur seals at Bouvetøya, Southern Ocean     

Greg Hofmeyr GJ  Bester MN  Kirkman SP  Lydersen C  Kovacs KM 《Marine pollution bulletin》2006,52(9):1077-1080

Entanglements of Antarctic fur seals Arctocephalus gazella were recorded during four summers from 1996 to 2002 at the subantarctic island, Bouvetøya. Rates of entanglement varied between 0.024% and 0.059%. These rates are low for a pinniped population and might be because of the geographic isolation of the haulout site. An apparent decrease in the levels of entanglement over the course of the study was likely due, at least in part, to the removal of entanglements by observers. At least two-thirds of entangling materials were generated by fishery sources. Since there is no known local source of anthropogenic marine pollution, seals become entangled either in waters distant from the island, or when materials drift into local waters. Significantly more subadults were found entangled than expected from the postulated population age class distribution.  相似文献   

Trends in fog frequencies in the Los Angeles Basin   总被引：1，自引：0，他引：1  

M.R. Witiw  Steve LaDochy 《Atmospheric Research》2008,87(3-4):293

Data from throughout the Los Angeles area were examined to determine the horizontal distribution of dense fog (visibility < 400 m) in the region and trends over time. The relationship between the occurrence of dense fog to the phase of two atmosphere–ocean cycles: the Pacific Decadal Oscillation (PDO) measured by the PDO Index and the Southern Oscillation measured by the Southern Oscillation Index (SOI) was investigated. In addition, the influence of the urban heat island and the amount of suspended particulate matter were assessed. For the three stations that had 22 or more years of data, we examined trends and the relation to atmosphere–ocean cycles. Results show a decrease in the occurrence of very low visibilities (< 400 m) at the stations in close proximity to the Pacific Ocean, Los Angeles International Airport (LAX) and Long Beach International Airport (LGB). Occurrence of the frequency of low visibilities at these two locations was also highly correlated with the phase of the PDO. Only a weak, non-statistically significant relationship was seen with the SOI. At Burbank, a reporting station about 30 km from the ocean, no trends were noted, and there was no evidence of a correlation with either the PDO Index or the SOI. In the Los Angeles Central Business District (CBD) when comparing dense fog occurrence in the early 1960s to a similar period in the early 2000s we saw a decrease in dense fog from a mean of 10 h per year to a mean of 3 h per year. Also contributing to the decrease was decreasing particulate pollution and increased urban warming. A downward trend in particulate concentrations coupled with an upward trend in urban temperatures were associated with a decrease in dense fog occurrence at both LAX and LGB. These trends were evident for the period 1966–1997, but appear to have ended by the late 1990s.  相似文献   

A model to predict stream water temperature across the conterminous USA          下载免费PDF全文

Catalina Segura  Peter Caldwell  Ge Sun  Steve McNulty  Yang Zhang 《水文研究》2015,29(9):2178-2195

Stream water temperature (t_s) is a critical water quality parameter for aquatic ecosystems. However, t_s records are sparse or nonexistent in many river systems. In this work, we present an empirical model to predict t_s at the site scale across the USA. The model, derived using data from 171 reference sites selected from the Geospatial Attributes of Gages for Evaluating Streamflow database, describes the linear relationship between monthly mean air temperature (t_a) and t_s. Multiple linear regression models are used to predict the slope (m) and intercept (b) of the t_a–t_s linear relation as a function of climatic, hydrologic and land cover characteristics. Model performance to predict t_s resulted in a mean Nash–Sutcliffe efficiency coefficient of 0.78 across all sites. Application of the model to predict t_s at additional 89 nonreference sites with a higher human alteration yielded a mean Nash–Sutcliffe value of 0.45. We also analysed seasonal thermal sensitivity (m) and found strong hysteresis in the t_a–t_s relation. Drainage area exerts a strong control on m in all seasons, whereas the cooling effect of groundwater was only evident for the spring and fall seasons. However, groundwater contributions are negatively related to mean t_s in all seasons. Finally, we found that elevation and mean basin slope are negatively related to mean t_s in all seasons, indicating that steep basins tend to stay cooler because of shorter residence times to gain heat from their surroundings. This model can potentially be used to predict climate change impacts on t_s across the USA. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献