How soil conservation affects the catchment sediment budget – a comprehensive study in the north Ethiopian highlands     

Jan Nyssen  Wim Clymans  Jean Poesen  Ine Vandecasteele  Sarah De Baets  Nigussie Haregeweyn  Jozef Naudts  Amanuel Hadera  Jan Moeyersons  Mitiku Haile  Jozef Deckers 《地球表面变化过程与地形》2009,34(9):1216-1233

An overall approach to assess the effectiveness of soil conservation measures at catchment scale is the comparison of sediment budgets before and after implementation of a catchment management programme. In the May Zeg‐zeg catchment (187 ha) in Tigray, north Ethiopia, integrated catchment management has been implemented since 2004: stone bunds were built in the whole catchment, vegetation was allowed to re‐grow on steep slopes and other marginal land, stubble grazing abandoned, and check dams built in gullies. Land use and management were mapped and analysed for 2000 and 2006, whereby particular attention was given to the quantification of changes in soil loss due to the abandonment of stubble grazing. Sediment yield was also measured at the catchment's outlet. A combination of decreased soil loss (from 14·3 t ha^–1 y^–1 in 2000 to 9·0 t ha^–1 y^–1 in 2006) and increased sediment deposition (from 5·8 to 7·1 t ha^–1 y^–1) has led to strongly decreased sediment yield (from 8·5 to 1·9 t ha^–1 y^–1) and sediment delivery ratio (from 0·6 to 0·21). This diachronic comparison of sediment budgets revealed that integrated catchment management is most effective and efficient and is the advisable and desirable way to combat land degradation in Tigray and other tropical mountains. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

Climatology of surface and near-bed temperature and salinity on the north-west European continental shelf for 1971–2000     

Barbara Berx  Sarah L. Hughes 《Continental Shelf Research》2009

A 30-year (1971–2000) temperature and salinity climatology is presented for surface and near-bed regions of the NW European shelf seas, with a resolution of 1/6^°$1/6^{°}$ longitude by 1/10^°$1/{10}^{°}$ latitude. The data have been extracted from the International Council for the Exploration of the Sea (ICES) data centre and supplemented by additional records from the World Ocean Data Centre (WODC). From the original data, which are irregularly distributed in space and time, the mean monthly temperature and salinity are calculated, as well as the climatic mean annual cycle. The climatology presented here is an improvement upon all existing climatologies presented in the literature for the NW European shelf; covering a wider area on a finer scale and including the surface and near-bed distribution of both temperature and salinity. Comparison of our data with existing climatologies shows good agreement, with differences occurring where our climatology is an improvement. This climatology, which will prove to be valuable to many users in the marine community, will be regularly updated and made available to all users via the ICES data centre.  相似文献   

A long-term nearshore wave hindcast for Ireland: Atlantic and Irish Sea coasts (1979–2012)     

Sarah Gallagher  Roxana Tiron  Frédéric Dias 《Ocean Dynamics》2014,64(8):1163-1180

The Northeast Atlantic possesses some of the highest wave energy levels in the world. The recent years have witnessed a renewed interest in harnessing this vast energy potential. Due to the complicated geomorphology of the Irish coast, there can be a significant variation in both the wave and wind climate. Long-term hindcasts with high spatial resolution, properly calibrated against available measurements, provide vital information for future deployments of ocean renewable energy installations. These can aid in the selection of adequate locations for potential deployment and for the planning and design of those marine operations. A 34-year (from 1979 to 2012), high-resolution wave hindcast was performed for Ireland including both the Atlantic and Irish Sea coasts, with a particular focus on the wave energy resource. The wave climate was estimated using the third-generation spectral wave model WAVEWATCH III®; version 4.11, the unstructured grid formulation. The wave model was forced with directional wave spectral data and 10-m winds from the European Centre for Medium Range Weather Forecasts (ECMWF) ERA-Interim reanalysis, which is available from 1979 to the present. The model was validated against available observed satellite altimeter and buoy data, particularly in the nearshore, and was found to be excellent. A strong spatial and seasonal variability was found for both significant wave heights, and the wave energy flux, particularly on the north and west coasts. A strong correlation between the North Atlantic Oscillation (NAO) teleconnection pattern and wave heights, wave periods, and peak direction in winter and also, to a lesser extent, in spring was identified.  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   

Chlorine abundances in meteorites     

Daniel Garrison  Sarah Hamlin  Donald Bogard 《Meteoritics & planetary science》2000,35(2):419-429

Abstract— We used the nuclear reaction ³⁷Cl (n,γ) ³⁸Ar, achieved during neutron irradiation for dating meteorites by the ³⁹Ar‐⁴⁰Ar technique, to calculate the elemental Cl concentration of 132 samples of 94 different meteorites (mostly finds) representing several different classes. determined k and ca concentrations are also reported. Total [Cl] varies considerably, both among meteorites of the same class and among different meteorite classes. The range in [Cl] is approximately 15–177 ppm for ordinary chondrites; approximately 24–650 ppm for enstatite chondrites; approximately 4–177 ppm for eucrites; approximately 7–128 ppm for mesosiderites; approximately 35–268 ppm for acapulcoites and lodranites; and approximately 12–507 ppm for winonaites and iron silicates. As expected, most differentiated meteorites have lower [Cl] compared to chondrites and iron silicates. Analyses of 11 interior samples (～0.1 g each) of a large L6 chondrite varied over 68–129 ppm, which is a measure of the homogeneity of Cl distribution. By evaluating Ar release during stepwise sample degassing, we separated the Cl into low‐temperature and high‐temperature components, the former of which may consist of terrestrial contamination. Most samples show low‐temperature Cl concentrations of <40 ppm, but for several samples terrestrial Cl contamination constitutes significant fractions of the total Cl. Among most differentiated meteorites, finds show considerably greater low‐temperature [Cl] compared to falls.  相似文献   

Globalisation, the Economic Crisis, and Small Enterprises in Makassar, Indonesia: Focusing on the Local Dimensions     

Sarah Turner 《Singapore journal of tropical geography》2000,21(3):336-354

It has been suggested that the economic crisis in Southeast Asia had a severe effect on small scale enterprises in the region. In this paper, I interpret the different consequences of this economic crisis ( krismon ) for small enterprises in the city of Makassar, Sulawesi, in the light of current globalisation debates. It is argued that for the majority of small enterprises, there have not been significant changes because of the relative isolation of Sulawesi within the Indonesian and global economies. However, for other small enterprises, there have been two significant changes indirectly linked to wider globalisation influences, because of the importance of conspicuous consumption amongst local cultural groups. In turn, this leads to an evaluation of both the strength of globalisation tendencies in the city, and the important influence of local cultural traits on the ways in which members of the local economy have responded to change.  相似文献   

Coeval deposition of transgressive and normal regressive stratal packages in a structurally controlled area of the Viking Formation,central Alberta,Canada     

Sarah K. Schultz  James A. MacEachern  Octavian Catuneanu  Shahin E. Dashtgard 《Sedimentology》2020,67(6):2974-3002

Variability in accommodation and sedimentation rates within a basin generates significant deviations in the along-strike stratal stacking patterns of systems tracts. This variability can lead to coeval depositional units that record the juxtaposition of transgressive (retrogradational) and regressive (progradational) stratal stacking patterns. In scenarios where transgressive and regressive units are deposited concurrently, challenges arise when attempting to correlate and place systems tracts into a sequence stratigraphic framework. In these scenarios, the maximum flooding surface records a high level of diachroneity, with the position of the surface variable throughout the stratigraphic column. In this study, Viking Formation (late Albian) deposits in the Western Canada Sedimentary Basin, central Alberta, Canada, preserve significant along-strike variability of palaeoshorelines that developed in response to autogenic processes as well as allogenic controls that were active during deposition. Specifically, structural reactivation of Precambrian basement structures during Viking deposition led to significant variability in depositional environments along the palaeoshoreline. The incremental basement reactivation of the Precambrian Snowbird Tectonic Zone influenced sedimentation patterns and the creation of anomalous zones of accommodation in localized areas of the basin. Across fault boundaries and within the anomalously thick strata, both progradational and retrogradational stacking patterns occur within broadly contemporaneous deposits, complicating the correlation of stratigraphic units. While the concomitant deposition of transgressive and regressive units has been documented in a number of modern marine analogues, the concept is rarely applied to ancient successions. By identifying along-strike variabilities in shoreline geometries and incorporating the autogenic and allogenic controls that were active during deposition, a more accurate sequence stratigraphic framework can be proposed.  相似文献   

Depth to the apparent redox potential discontinuity (aRPD) as a parameter of interest in marine benthic habitat quality models     

Travis G. Gerwing  Kieran Cox  Alyssa M. Allen Gerwing  Charmaine N. Carr-Harris  Sarah E. Dudas  Francis Juanes 《国际泥沙研究》2018,33(2):149-156

The usefulness of the apparent redox potential discontinuity (aRPD) in assessments of marine benthic habitat quality was explored at two intertidal mudflats along the north Pacific coast of Canada. Two transects were established at each intertidal site, with three sediment biogeochemistry cores collected from each transect four times over the summer of 2016. Measurements of the sediment pore water dissolved oxygen (DO) content and redox (Eh) conditions were taken at the surface of the core (measured vertically), as well as at increasing depths (1 cm between readings) into the sediment (measured horizontally through predrilled holes in the biogeochemistry corer). While oxic, anoxic, oxidized, and reduced sediment pore water was observed above and below the aRPD, in general, sediment above the aRPD had higher DO content, and higher Eh values than sediment below the aRPD. Therefore, the aRPD depth can be used as a relative indicator of sediment pore water DO and Eh conditions: sediment with a deeper aRPD depth has more available DO, and the pore water has higher Eh values (more oxidized or less reduced) than sediment with a shallower aRPD depth. As such, the aRPD depth is a useful parameter to include in models that assess the quality of marine benthic habitats.  相似文献   

Delineation of precipitation regions in two Canadian study areas: the role of the temporal resolution of the precipitation data     

Sarah Irwin  Slobodan P. Simonovic  Donald H. Burn 《水文科学杂志》2017,62(13):2061-2071

The identification of homogeneous precipitation regions has value in many water resources engineering applications (infrastructure planning, design, operations; climate forecasting, modelling). The objective of this paper is to assess the sensitivity of precipitation regions to the temporal resolution (monthly, seasonal, annual and the annual maximum series) of the data. The presented method uses the fuzzy c-means clustering algorithm to partition climate sites into statistically homogeneous precipitation regions. The regions are validated using an approach based on L-moment statistics. The method is conducted in two climatically different study areas in western and eastern Canada. There does not appear to be a relationship between the spatial distributions of the regions formed using different temporal resolutions of the precipitation data. It is recommended to delineate precipitation regions that are specific to the task at hand, and to select a temporal resolution that is consistent with the final application of the regional precipitation dataset.