Patch use and exploratory movements of a resident houbara bustard in northern Saudi Arabia     

Yolanda van Heezik  Philip J. Seddon 《Journal of Arid Environments》2002,50(4):683

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The rate of grain release by pore-ice sublimation in cold-aeolian environments   总被引：1，自引：0，他引：1  

Deanna van Dijk  Jane Law 《Geografiska Annaler: Series A, Physical Geography》2003,85(1):99-113

Pore‐ice sublimation is a prerequisite for aeolian activity in cold environments where surface sediments hold significant amounts of frozen water. Few quantitative studies have defined the rate of grain release from cemented surfaces by pore‐ice sublimation. In 1996–1997, controlled field experiments at Presqu'ile Beach, Ontario, were implemented to measure sediment release from frozen surfaces. The release rates were compared to the local wind regime, ambient temperature and humidity. In additional field experiments, the effect of sediment water content on grain release by sublimation was examined. From the experimental results, an equation which predicts grain release based on local wind speed, ground temperature, humidity, and surface water content is proposed. Predicted release rates show reasonable agreement with natural deflation measured on the beach at Presqu'ile Provincial Park.  相似文献   

Shear wave statics using receiver functions   总被引：1，自引：0，他引：1  

D. van Manen  J. O. A. Robertsson  A. Curtis  R. Ferber  H. Paulssen 《Geophysical Journal International》2003,153(3):F1-F5

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Joint inversion of local, regional and teleseismic data for crustal thickness in the Eurasia–Africa plate boundary region     

Federica Marone  Mark van der Meijde  Suzan van der Lee  Domenico Giardini 《Geophysical Journal International》2003,154(2):499-514

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Receiver function study of the Hellenic subduction zone: imaging crustal thickness variations and the oceanic Moho of the descending African lithosphere   总被引：3，自引：0，他引：3  

X. Li  G. Bock  A. Vafidis  R. Kind  H.-P. Harjes  W. Hanka  K. Wylegalla  M. van der Meijde  X. Yuan 《Geophysical Journal International》2003,155(2):733-748

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Wind erosion from military training lands in the Mojave Desert, California, U.S.A.   总被引：1，自引：0，他引：1  

Simon J. van Donk  Xuewen Huang  Edward L. Skidmore  Alan B. Anderson  Dick L. Gebhart  Valerie E. Prehoda  Elizabeth M. Kellogg 《Journal of Arid Environments》2003,54(4):687-703

Military training activities reduce vegetation cover, disturb crusts, and degrade soil aggregates, making the land more vulnerable to wind erosion. The objective of this study was to quantify wind erosion rates for typical conditions at the Marine Corps Air Ground Combat Center, Twentynine Palms, CA, U.S.A. Five Big Spring Number Eight (BSNE) sampler stations were installed at each of five sites. Each BSNE station consisted of five BSNE samplers with the lowest sampler at 0·05 m and the highest sampler at 1·0 m above the soil surface. Once a month, sediment was collected from the samplers for analysis. Occurrence of saltating soil aggregates was recorded every hour using Sensits, one at each site. The site with the most erosion had a sediment discharge of 311 kg m⁻¹ over a period of 17 months. Other sites eroded much less because of significant rock cover or the presence of a crust. Hourly sediment discharge was estimated combining hourly Sensit count and monthly sediment discharge measured using BSNE samplers. More simultaneously measured data are needed to better characterize the relationship between these two and reconstruct a detailed time-series of wind erosion. This measured time-series can then be used for comparison with simulation results from process-based wind erosion models such as the Wind Erosion Prediction System (WEPS), once it has been adapted to the unique aspects of military lands.  相似文献   

Atmospheric nitrogen inputs into the North Sea: effect on productivity     

Gerrit de Leeuw  Lucinda Spokes  Tim Jickells  Carsten Ambelas Skjth  Ole Hertel  Elisabetta Vignati  Susanne Tamm  Michael Schulz  Lise-Lotte Srensen  Britta Pedersen  Laura Klein  K. Heinke Schlünzen 《Continental Shelf Research》2003,23(17-19):1743

The ANICE (Atmospheric Nitrogen Inputs into the Coastal Ecosystem) project addressed the atmospheric deposition of nitrogen to the North Sea, with emphasis on coastal effects. ANICE focused on quantifying the deposition of inorganic nitrogen compounds to the North Sea and the governing processes. An overview of the results from modelling and experimental efforts is presented. They serve to identify the role of the atmosphere as a source of biologically essential chemical species to the marine biota. Data from the Weybourne Atmospheric Observatory (UK) are used to evaluate the effect of short episodes with very high atmospheric nitrogen concentrations. One such episode resulted in an average deposition of 0.8 mmol N m⁻² day⁻¹, which has the potential to promote primary productivity of 5.3 mmol C m⁻² day⁻¹. This value is compared to long-term effects determined from model results. The total calculated atmospheric deposition to the North Sea in 1999 is 948 kg N km⁻¹, i.e. 0.19 mmol N m⁻² day⁻¹ which has the potential to promote primary productivity of 1.2 mmol C m⁻² day⁻¹. Detailed results for August 1999 show strong gradients across the North Sea due to adjacent areas where emissions of NO_x and NH₃ are among the highest in Europe. The average atmospheric deposition to the southern part of the North Sea in August 1999 could potentially promote primary production of 2.0 mmol C m⁻² day⁻¹, i.e. 5.5% of the total production at this time of the year in this area of the North Sea. For the entire study area the atmospheric contribution to the primary production per m² is about two-third of this value. Most of the deposition occurs during short periods with high atmospheric concentrations. This atmospheric nitrogen is almost entirely anthropogenic in origin and thus represents a human-induced perturbation of the ecosystem.  相似文献   

Towards non-linear inversion for characterization of time-lapse phenomena through numerical modelling     

A. Abubakar  P.M. van den Berg  J.T. Fokkema 《Geophysical Prospecting》2003,51(4):285-293

We compare two geophysical survey measurements of the same type made at different times in order to characterize the change in the geological medium during the elapsed time. The aim of this study is to develop a strategy using a full non-linear inversion algorithm as the interpretation tool. In this way, not only the location and the form of the changes are recovered, but also the changes in the material parameters of the geological medium can be estimated. In order to solve this fully non-linear problem, the so-called ‘multiplicative regularized contrast source inversion’ (MR-CSI) method is employed. The unique property of this iterative method is that it does not solve the forward problem at each iterative step. This makes it possible to use the non-linear inversion algorithm for large-scale computation problems. The numerical results show that by taking into account the non-linear nature of the problem, interpretation of the time-lapse data can be significantly improved, compared with that obtained using linear inversion.  相似文献   

Lower crustal melting and the role of open-system processes in the genesis of syn-orogenic quartz diorite–granite–leucogranite associations: constraints from Sr–Nd–O isotopes from the Bandombaai Complex, Namibia     

Tina van de Flierdt  Stephan Hoernes  Stefan Jung  Peter Masberg  Edgar Hoffer  Urs Schaltegger  Hans Friedrichsen 《Lithos》2003,67(3-4):205-226

The Bandombaai Complex (southern Kaoko Belt, Namibia) consists of three main intrusive rock types including metaluminous hornblende- and sphene-bearing quartz diorites, allanite-bearing granodiorites and granites, and peraluminous garnet- and muscovite-bearing leucogranites. Intrusion of the quartz diorites is constrained by a U–Pb zircon age of 540±3 Ma.

Quartz diorites, granodiorites and granites display heterogeneous initial Nd- and O isotope compositions (_{Nd (540 Ma)}=−6.3 to −19.8; δ¹⁸O=9.0–11.6‰) but rather low and uniform initial Sr isotope compositions (⁸⁷Sr/⁸⁶Sr_initial=0.70794–0.70982). Two leucogranites and one aplite have higher initial ⁸⁷Sr/⁸⁶Sr ratios (0.70828–0.71559), but similar initial _Nd (−11.9 to −15.8) and oxygen isotope values (10.5–12.9‰). The geochemical and isotopic characteristics of the Bandombaai Complex are distinct from other granitoids of the Kaoko Belt and the Central Zone of the Damara orogen. Our study suggests that the quartz diorites of the Bandombaai Complex are generated by melting of heterogeneous mafic lower crust. Based on a comparison with results from amphibolite-dehydration melting experiments, a lower crustal garnet- and amphibole-bearing metabasalt, probably enriched in K₂O, is a likely source rock for the quartz diorites. The granodiorites/granites show low Rb/Sr (<0.6) ratios and are probably generated by partial melting of meta-igneous (intermediate) lower crustal sources by amphibole-dehydration melting. Most of the leucogranites display higher Rb/Sr ratios (>1) and are most likely generated by biotite-dehydration melting of heterogeneous felsic lower crust. All segments of the lower crust underwent partial melting during the Pan-African orogeny at a time (540 Ma) when the middle crust of the central Damara orogen also underwent high T, medium P regional metamorphism and melting. Geochemical and isotope data from the Bandombaai Complex suggest that the Pan-African orogeny in this part of the orogen was not a major crust-forming episode. Instead, even the most primitive rock types of the region, the quartz diorites, represent recycled lower crustal material.  相似文献   

Use of Geomorphological Information in Indirect Landslide Susceptibility Assessment   总被引：31，自引：6，他引：31  

van Westen  C. J.  Rengers  N.  Soeters  R. 《Natural Hazards》2003,30(3):399-419

The objective of this paper is to evaluate the importance of geomorphological expert knowledge in the generation of landslide susceptibility maps, using GIS supported indirect bivariate statistical analysis. For a test area in the Alpago region in Italy a dataset was generated at scale 1:5,000. Detailed geomorphological maps were generated, with legends at different levels of complexity. Other factor maps, that were considered relevant for the assessment of landslide susceptibility, were also collected, such as lithology, structural geology, surficial materials, slope classes, land use, distance from streams, roads and houses. The weights of evidence method was used to generate statistically derived weights for all classes of the factor maps. On the basis of these weights, the most relevant maps were selected for the combination into landslide susceptibility maps. Six different combinations of factor maps were evaluated, with varying geomorphological input. Success rates were used to classify the weight maps into three qualitative landslide susceptibility classes. The resulting six maps were compared with a direct susceptibility map, which was made by direct assignment of susceptibility classes in the field. The analysis indicated that the use of detailed geomorphological information in the bivariate statistical analysis raised the overall accuracy of the final susceptibility map considerably. However, even with the use of a detailed geomorphological factor map, the difference with the separately prepared direct susceptibility map is still significant, due to the generalisations that are inherent to the bivariate statistical analysis technique.  相似文献