Surface texture analysis of southern Tuli Basin sediments: Implications for Limpopo Valley geoarchaeological contexts     

Joel C. Le Baron  Stefan W. Grab  Kathleen Kuman 《Journal of African Earth Sciences》2011,59(4-5):384-394

The Hackthorne 1 site (southern Tuli Basin, South Africa) is situated on a sand-covered plateau adjacent to the Limpopo River Valley. Although the site is well known for its Stone Age archaeology, the past environmental contexts (particularly sedimentological/geomorphological) are not well known. We examine the Hackthorne sand grain surface textures, so as to provide some insight on the site specific and regional depositional history. Quartz sands at Hackthorne were collected from surface sands and from underlying weathered calcrete. SEM analysis was performed on sand grains, through which several mechanical and chemical microtextures were identified. Microtextures typical of fluvial environments were found only on grains derived from the plateau calcrete host sediment, whilst the surface sands exhibited only textures associated with aeolian environments. The results indicate that the calcrete host sediment is composed of alluvium, and that the surface sands mantling the Hackthorne Plateau are not deflated from the alluvial deposits in the Limpopo Valley, but may rather be derived from distant aeolian sources. The deposition of aeolian sands is consistent with OSL dates which place sand deposition, or remobilization, at 23 and 15 kya, periods in southern Africa associated with increased aridity.  相似文献   

Response surface methodology for lead biosorption on Aspergillus terreus     

F. J. Cerino Córdova Ph.D.  A. M. García León Ph.D.  R. B. Garcia Reyes Ph.D.  M. T. Garza González Ph.D.  E. Soto Regalado Ph.D.  M. N. Sánchez González Ph D.  I. Quezada López 《International Journal of Environmental Science and Technology》2011,8(4):695-704

A central composite face-centered design was used to study and to optimize lead biosorption from aqueous solution on Aspergillus terreus biomass. Four factors such as stirring speed, temperature, solution pH and biomass dose at different levels were studied.The hierarchical quadratic model were established by adding replicates at the central point and axial points to the initial full factorial design (2⁴). The percentage removal of lead was affected by biomass dose, pH, and interactions between pH and biomass dose, pH and stirring speed, pH and temperature. The hierarchical quadratic model described adequately the response surface based on the adjusted determination coefficient (R² _Adj= 0.97) and the adequate precision ratio (42.21). According to this model, the optimal conditions to remove lead completely from aqueous solutions (at initial lead concentration of 50 mg/L and solutions of 100 mL) with Aspergillus terreus were at pH 5.2, 50 °C, stirring speed of 102/min and a biomass dose of 139 mg.The response surface methodology can be used to determine the optimal conditions for metal adsorption on several adsorbents. In addition, results reported in this research demonstrated the feasibility of employing A. terreus as biosorbent for lead removal.  相似文献   

Geostatistical approach for the assessment of the water reservoir capacity in arid regions: a case study of the Akdarya reservoir,Uzbekistan     

Shavkat Rakhmatullaev  Antoine Marache  Frédéric Huneau  Philippe Le Coustumer  Masharif Bakiev  Mikael Motelica-Heino 《Environmental Earth Sciences》2011,63(3):447-460

The paper presents the results of a new geostatistical approach to generate bathymetric surface models from point measurement converted into continuous contour surfaces of reservoir bottoms in Uzbekistan. Sedimentation of reservoirs raises engineering, environmental and economical issues for the communities around the world in areas affected by a strong water deficit. Because of Uzbekistan’s arid climatic conditions, and uneven spatial and temporal water resources distribution, responsive and innovative water availability assessment surveys of all major water reservoirs are required. Bathymetric surveying is a traditional method that is carried out for the estimation of reservoir volumes and surface areas of the corresponding reservoir stages in order to assess the water availability. Volume and surface area differences derived from multiple surveys of a reservoir provide storage loss estimates over time due to sedimentation. However, two main factors, such as intensive field data measurement and post data-processing, often limit the frequency of these surveys. Alternatively, innovative depth measurement technologies coupled with contouring and surface mapping programs provide automated reservoir volume and surface area calculations. This significantly reduces time, workload and financial burdens for reservoir sedimentation projects. This research proposes the use of geostatistical approach to assess the reservoir sedimentation in the Akdarya reservoir of Uzbekistan. The geostatistical approach includes (semi-) variogram analysis and interpolation (kriging and simulations—turning bands) techniques predicting values at unsampled locations for generating digital bathymetric surface models of reservoir bottom conditions in order to calculate the volume and surface area at a given water elevation. The simulation enables to have range of reservoir volumes and surface areas with the same probability, in comparison to the kriging and traditional methods. This gives a real estimation of the resource availability for water operators to manage natural resources and hydraulic infrastructure in a sustainable manner.  相似文献   

农村土地流转近期研究评述与启示     

苑韶峰  孙乐  杨丽霞  刘欣玫 《上海国土资源》2011,32(4):49-53

本文采用文献资料法与比较分析法,从农地流转影响因素、流转效率与流转效果、制度创新、国外相关政策比较等方面综合评述了国内外文献资料在农村土地流转方面的研究进展。并从加强在农地流转潜力、制度创新和分区域的农地流转等方面提出今后该方面的研究应当努力的方向。  相似文献   

An Improved Parallel Multiple-point Algorithm Using a List Approach   总被引：15，自引：8，他引：7  

Julien Straubhaar  Philippe Renard  Gr��goire Mariethoz  Roland Froidevaux  Olivier Besson 《Mathematical Geosciences》2011,43(3):305-328

Among the techniques used to simulate categorical variables, multiple-point statistics is becoming very popular because it allows the user to provide an explicit conceptual model via a training image. In classic implementations, the multiple-point statistics are inferred from the training image by storing all the observed patterns of a certain size in a tree structure. This type of algorithm has the advantage of being fast to apply, but it presents some critical limitations. In particular, a tree is extremely RAM demanding. For three-dimensional problems with numerous facies, large templates cannot be used. Complex structures are then difficult to simulate. In this paper, we propose to replace the tree by a list. This structure requires much less RAM. It has three main advantages. First, it allows for the use of larger templates. Second, the list structure being parsimonious, it can be extended to include additional information. Here, we show how this can be used to develop a new approach for dealing with non-stationary training images. Finally, an interesting aspect of the list is that it allows one to parallelize the part of the algorithm in which the conditional probability density function is computed. This is especially important for large problems that can be solved on clusters of PCs with distributed memory or on multicore machines with shared memory.  相似文献   

Multiple-Point Statistics for Modeling Facies Heterogeneities in a Porous Medium: The Komadugu-Yobe Alluvium,Lake Chad Basin     

Mathieu?Le?CozEmail author  Pierre?Genthon  Pierre?M.?Adler 《Mathematical Geosciences》2011,43(7):861-878

Multiple-point statistics are used to model facies heterogeneities in the vadose zone of the Komadugu-Yobe River valley (southeastern Niger) which is presently submitted to an undergoing intensive agricultural development; therefore, increasing quantitative and qualitative pressures are exerted on groundwater resources. The sand–clay heterogeneities are analyzed by means of a Landsat image acquired during a high flow period over a 160 km stretch in the downstream part of the valley and a set of 50 boreholes drilled near the town of Diffa (4 km×4 km area). The horizontal variograms of heterogeneities are characterized by a noticeably constant length scale of 380 m and clayey objects are shown to be randomly distributed in space according to a Poisson process. A set of two-dimensional vertical images is built based on a Boolean procedure and the Snesim algorithm is used to simulate synthetic three-dimensional media. When the vertical correlation length is fitted, the three-dimensional model satisfactorily reproduces the second order statistics of heterogeneities and the specific facies patterns.  相似文献   

Structure and seasonal variability of fish food webs in an estuarine tropical marine protected area (Senegal): Evidence from stable isotope analysis     

Djibril Faye  Luis Tito de Morais  Jean Raffray  Oumar Sadio  Omar Thiom Thiaw  Franois Le Loc&#x;h 《Estuarine, Coastal and Shelf Science》2011,92(4):69

  相似文献   

Empirical design of scour protections around monopile foundations: Part 1: Static approach     

Leen De Vos  Julien De Rouck  Peter Troch  Peter Frigaard 《Coastal Engineering》2011

Together with new opportunities, offshore wind farms raise new engineering challenges. An important aspect relates to the erosion of bottom material around the foundation of the wind turbines, caused by the local increase of the wave and current induced flow velocities by the pile's presence. Typically, the expected scour has a considerable impact on the stability and dynamic behavior of the wind turbine and a scour protection is placed to avoid erosion of the soil close to the foundation. Although much experience exists on the design of scour protections around bridge piers (which are placed in a current alone situation), at present, little design guidelines exist for the specific case of a scour protection around a monopile foundation subjected to a combined wave and current loading.  相似文献   

岔巴沟、大理河与无定河水土保持减水减沙作用的尺度效应   总被引：2，自引：0，他引：2  

綦俊谕  蔡强国  蔡乐  孙莉英 《地理科学进展》2011,30(1):95-102

运用经验公式法、双累积曲线法和不同系列对比法计算出岔巴沟、大理河与无定河流域在20世纪70年代水土保持综合措施的平均减水效益分别为14.47%、20.22%和20.78%,平均减沙效益为64.97%、43.62%和47.26%.对计算结果进行分析发现,用3种方法对岔巴沟、大理河与无定河流域水土保持综合措施减水减沙效益的...  相似文献   

The possibilities and pitfalls presented by a pragmatic approach to ecosystem service valuation in an arid biodiversity hotspot     

P.J. O’Farrell  W.J. De LangeD.C. Le Maitre  B. ReyersJ.N. Blignaut  S.J. MiltonD. Atkinson  B. EgohA. Maherry  C. ColvinR.M. Cowling 《Journal of Arid Environments》2011,75(6):612-623

Arid regions are home to unique fauna, flora, and vulnerable human populations, and present a challenge for sustainable land-use management. We undertook an assessment and valuation of three key services, grazing, tourism and water supply in the arid Succulent Karoo biome in western South Africa - a globally recognised biodiversity hotspot. We were looking for ways and values that could be used to promote conservation in this region through the adoption of sustainable land-use practices which have human welfare benefits. Our study adopted a variety of methods in valuing these services in developing ranges of values for these services. At the biome level, total annual values ranged from $ 19-114 million for grazing, $ 2-$ 20 million for tourism, and $ 300-3120 million for water. These values are generally low compared with values derived for other biomes and regions and do not adequately reflect known dependence and the importance of ecosystem services to the residents of this biome. The ecosystems here provide small but critical benefits enabling communities to sustain themselves and small changes in service levels can have major welfare effects. Highlighting these sensitivities will require finding more appropriate ways to link ecological and social factors.  相似文献