Calculations of upper-mantle P-wave velocity anisotropies

Discovery of anisotropy for upper-mantle P-wave velocities has resulted recently in many laboratory determinations of velocities for natural mantle material, either by direct measurement on rock samples or through calculations based on single-crystal elastic constants, fabrics and modal compositions Comparison of field and laboratory data provides gross constraints for convection processes and flow mechanisms. As natural peridotites yeidl a wide range of maximum seismic anisotropies, their depth of origin and deformation history are inferred from pyroxene geobarometry and geothermometry, and from stress estimates derived from neoblast grain sizes. Large maximum anisotropies (ca. 1.0 km/s) are typical of samples with fabrics strengthened by low-temperature/highstress deformation related to emplacement. Other highly anisotropic mantle material includes peridotites beneath continental rifts and thinned continental crust. Maximum anisotropies for ordinary suboceanic and infracontinental peridotites are generally in the range of the field data (0.3–0.6 km/s) and support a model with [010]_ol nearly vertical (in accord with observations on ophiolites) and [100]_ol subparallel to the spreading direction. On the basis of fabric data, seismic anisotropy should decrease with depth.     

东亚区域陆面过程方案Noah和Noah-MP的比较评估

文章对天气研究和预报(WRF)模式中两套陆面物理过程参数化方案:Noah及Noah-MP,在整个东亚区域做了评估。评估时间分别为2013年1和7月。通过对地表通量、2 m温度、10 m风速、地表温度、第一层(5 cm)及第二层(25 cm)土壤含水量和第一层(5 cm)及第三层(70 cm)土壤温度的偏差和均方根误差的评估,发现:(1)与Noah陆面参数化方案相比,冬季,Noah-MP方案模拟的地表感热通量在大部分区域偏低,而对地表潜热通量的模拟在大部分区域偏高;夏季,Noah-MP方案对感热通量的模拟值,在印度次大陆、中国西部和相邻区域以及中国东北及其以北地区偏低,其他地区偏高,而对地表潜热通量的模拟在大部分地区偏高,而且幅度明显高于1月。(2)Noah-MP方案提高了土壤水分和土壤温度在东亚区域的整体模拟效果。(3)相较于Noah方案,Noah-MP方案模拟的2 m温度和10 m风的误差较小,特别对印度大陆和高寒地区的2 m温度模拟有较大幅度的提高。此研究证明了Noah-MP在东亚区域的应用优势,为WRF/Noah-MP在未来的进一步业务应用提供了一定的参考依据。     

Realtime Conferencing in GIS

Most GIS applications support multi-user facilities only to the extent that many people can access the same data as if they were each the only user. For collaborative work, it is beneficial for participants to be able to browse, annotate and query the data with full awareness of each other. Groupware or Computer Supported Cooperative Work (CSCW) provides support for groups of people to participate in virtual conferences from different locations. We demonstrate the advantages to be gained by applying CSCW to GIS and describe GroupARC, an application enabling GIS data to be simultaneously browsed, queried and annotated by many participants.     

VS2DRTI: Simulating Heat and Reactive Solute Transport in Variably Saturated Porous Media

Variably saturated groundwater flow, heat transport, and solute transport are important processes in environmental phenomena, such as the natural evolution of water chemistry of aquifers and streams, the storage of radioactive waste in a geologic repository, the contamination of water resources from acid‐rock drainage, and the geologic sequestration of carbon dioxide. Up to now, our ability to simulate these processes simultaneously with fully coupled reactive transport models has been limited to complex and often difficult‐to‐use models. To address the need for a simple and easy‐to‐use model, the VS2DRTI software package has been developed for simulating water flow, heat transport, and reactive solute transport through variably saturated porous media. The underlying numerical model, VS2DRT, was created by coupling the flow and transport capabilities of the VS2DT and VS2DH models with the equilibrium and kinetic reaction capabilities of PhreeqcRM. Flow capabilities include two‐dimensional, constant‐density, variably saturated flow; transport capabilities include both heat and multicomponent solute transport; and the reaction capabilities are a complete implementation of geochemical reactions of PHREEQC. The graphical user interface includes a preprocessor for building simulations and a postprocessor for visual display of simulation results. To demonstrate the simulation of multiple processes, the model is applied to a hypothetical example of injection of heated waste water to an aquifer with temperature‐dependent cation exchange. VS2DRTI is freely available public domain software.     

Dynamics of soil erosion rates and controlling factors in the Northern Ethiopian Highlands – towards a sediment budget

This paper analyses the factors that control rates and extent of soil erosion processes in the 199 ha May Zegzeg catchment near Hagere Selam in the Tigray Highlands (Northern Ethiopia). This catchment, characterized by high elevations (2100–2650 m a.s.l.) and a subhorizontal structural relief, is typical for the Northern Ethiopian Highlands. Soil loss rates due to various erosion processes, as well as sediment yield rates and rates of sediment deposition within the catchment (essentially induced by recent soil conservation activities), were measured using a range of geomorphological methods. The area‐weighted average rate of soil erosion by water in the catchment, measured over four years (1998–2001), is 14·8 t ha^?1 y^?1, which accounts for 98% of the change in potential energy of the landscape. Considering these soil loss rates by water, 28% is due to gully erosion. Other geomorphic processes, such as tillage erosion and rock fragment displacement by gravity and livestock trampling, are also important, either within certain land units, or for their impact on agricultural productivity. Estimated mean sediment deposition rate within the catchment equals 9·2 t ha^?1 y^?1. Calculated sediment yield (5·6 t ha^?1 y^?1) is similar to sediment yield measured in nearby catchments. Seventy‐four percent of total soil loss by sheet and rill erosion is trapped in exclosures and behind stone bunds. The anthropogenic factor is dominant in controlling present‐day erosion processes in the Northern Ethiopian Highlands. Human activities have led to an overall increase in erosion process intensities, but, through targeted interventions, rural society is now well on the way to control and reverse the degradation processes, as can be demonstrated through the sediment budget. Copyright © 2007 John Wiley & Sons, Ltd.     

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

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.     

Assessment of an ASTER-generated DEM for 2D hydrodynamic flood modeling

Flood modeling often provides inputs to flood hazard management. In the present work we studied the flooding characteristics in the data scarce region of the Lake Tana basin at the source of the Blue Nile River. The study required to integrate remote sensing, GIS with a two-dimensional (2D) module of the SOBEK flood model. The resolution of the topographic data in many areas, such as the Lake Tana region, is commonly too poor to support detailed 2D hydrodynamic modeling. To overcome such limitations, we used a Digital Elevation Model (DEM) which was generated from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) image. A GIS procedure is developed to reconstruct the river terrain and channel bathymetry. The results revealed that a representation of the river terrain largely affects the simulated flood characteristics. Simulations indicate that effects of Lake Tana water levels propagate up to 13 km along the Ribb River. We conclude that a 15 m resolution ASTER DEM can serve as an input to detailed 2D hydrodynamic modeling in data scarce regions. However, for this purpose it is necessary to accurately reconstruct the river terrain geometry and flood plain topography based on ground observations by means of a river terrain model.     

eDNA监测方法标准化框架及未来图景

eDNA (environmental DNA)是指从环境样品（水体、土壤、沉积物、空气、混合物等）中提取的DNA,是各种生物的DNA混合物,区别于传统从单物种样品中提取的DNA。eDNA监测是指从环境样品中提取DNA,用物种特异性引物或特定DNA metabarcoding引物对其进行扩增测序、分类学分析、相对丰度分析、功能预测等,以监测环境中是否存在某特定物种,或者获得环境中物种组成、群落结构、生态功能等相关信息。eDNA监测主要应用在特定物种监测检出、生物多样性调查评估、群落结构和功能分析、生态系统过程分析评估等领域。eDNA监测可以应用在陆地、水体、空气、器物表面、生物（内）表面等任何有可能存在不确定DNA的场景。因为eDNA监测的非侵入性、灵敏检出、大类群检出、易标准化方法与结果、低人力物力时间成本、结果可核查等特点,未来很有希望发展成为一种常规的物种监测、群落功能预测、生态过程分析的方法,对象可涵盖所有生境条件下的所有生物类群。但要实现这个图景,需要从普遍性和特殊性层面完成eDNA监测技术链条中10个关键环节的技术标准化：样品重复数设计、采样时间设计、采样点设计、采样方法设...     

Using recovery data to extend the effective duration of pumping tests

Collection of water-level recovery data is a common practice for pumping tests. The resulting data can provide some of the most useful information from the tests, but are rarely used to their full value. van der Kamp (1989) proposed a general method that uses recovery data to extend the effective duration of pumping. The method is straightforward to implement and applicable for simple or complex hydrogeologic settings. The only assumption invoked is that the response remains linear such that the principle of superposition can be applied. No other assumptions about the properties of the aquifer are required. The method can greatly increase the value of pumping tests by extending the effective duration of the tests for as long as significant residual drawdowns are observed.