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11.
The soil water retention function is needed for modeling multiphase flow in porous media. Traditional techniques for measuring the soil water retention function, such as the hanging water column or pressure cell methods, yield average water retention data which have to be modeled using inverse procedures to extract relevant point parameters. In this study, we have developed a technique for directly measuring multiple point (pixel-scale) water retention curves for a repacked sand material using 2-D neutron radiography. Neutron radiographic images were obtained under quasi-equilibrium conditions at nine imposed basal matric potentials during monotonic drying of Flint sand at the High Flux Isotope Reactor (HFIR) Cold Guide (CG) 1D beamline at Oak Ridge National Laboratory. All of the images were normalized with respect to an image of the oven dry sand column. Volumetric water contents were computed on a pixel by pixel basis using an empirical calibration equation after taking into account beam hardening and geometric corrections. Corresponding matric potentials were calculated from the imposed basal matric potential and pixel elevations. Volumetric water content and matric potential data pairs corresponding to 120 selected pixels were used to construct 120 point water retention curves. Each curve was fitted to the Brooks and Corey equation using segmented non-linear regression in SAS. A 98.5% convergence rate was achieved resulting in 115 estimates of the four Brooks and Corey parameters. A single Brooks and Corey point water retention function was constructed for Flint sand using the median values of these parameter estimates. This curve corresponded closely with the point Brooks and Corey function inversely extracted from the average water retention data using TrueCell. Forward numerical simulations performed using HYDRUS 1-D showed that the cumulative outflows predicted using the point Brooks and Corey functions from both the direct (neutron radiography) and inverse (TrueCell) methods were in good agreement with independent measurements of cumulative outflow determined with a transducer. Our results indicate that neutron radiography can be used to quantify the point water retention curve of homogeneous mineral particles. Further research will be needed to extend this approach to more heterogeneous porous media. 相似文献
12.
A method for the rapid detection of cyanobacteria (blue‐green algae) and their differentiation from eukaryotic algae in natural phytoplankton assemblages is presented. Fluorescence emission of photosynthetic pigments at 670 nm was measured using a microplate fluorescence reader when excited at two different wavelengths – 485 nm and 590 nm. The ratio of fluorescence excited at these wavelengths (590 nm/485 nm) was proportional to the ratio of cyanobacteria and eukaryotic algae, which was determined by the in situ spectrofluorometer for the phytoplankton quantification. The fluorescence intensity was equal to the total chlorophyll‐a content. These two fluorescence values can provide the first warning on a development of potentially toxic cyanobacteria in water. 相似文献
13.
Techniques for simultaneous quantification of wind and water erosion in semi-arid regions 总被引：3，自引：0，他引：3
Wind and water erosion are usually studied as two separate processes. However, in semi-arid zones both processes contribute significantly to soil degradation. Whereas for water erosion the direction of sediment transport is controlled by topography, in wind erosion the direction of transport is controlled by the wind direction. Furthermore, the spatial pattern of erosion and deposition for wind erosion is determined by the spatial distribution of source material, soil erodibility factors and non-erodible roughness elements. Given this difference in dependence on topography, different approaches are needed to determine the mass balance for a given area. For water erosion, the research area has to be defined such that no input of sediment occurs, whereas in wind erosion the input and output fluxes of sediment should be measured, or a non-eroding boundary should be created.In semi-arid regions, wind erosion events are often followed immediately by heavy rain. As wind and water erosion occur almost simultaneously at the same site, the effect of wind and water erosion at a given site should be studied concurrently. To do so, a number of measurement techniques with different spatial and temporal scales are necessary. The research should be started at the scale of a Sahelian field. For a complete insight into the processes at a site, the research should include measurement techniques that quantify the impact of wind and water erosion separately and techniques that quantify their combined effect. 相似文献
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15.
Assessing desertification 总被引：8，自引：2，他引：8
It is widely recognized that desertification is a serious threat to arid and semiarid environments—which cover 40% of the global land surface and are populated by approximately 1 billion humans. Given the potential relevance of this problem, it is surprising that there is no consensus on the proper way to assess the desertification status of a piece of land. During the last 70 years, conflicting definitions have produced both different assessment methodologies and divergent estimates. Contrary to conceptual issues on desertification, assessment methodologies have not been reviewed comprehensively. Here, we critically review the most common methodologies to assess desertification, and describe their principal consequences on scientific and social arenas.We show that desertification assessment has shifted from simple appraisals of the interannual movement of desert boundaries to complex multivariate field surveys, to practical methodologies based on indicators of ecosystem functioning, such as rain use efficiency. Although often regarded as an evidence of stagnation and failure, these methodologies reflect the progress that desertification ecology has experienced. Future challenges for properly assessing desertification are (1) the lack of reference situations against which actual desertification could be compared, and (2) the difficulties that appear when desertification operates through structural rather than functional ecosystem changes.The coexistence of conflicting definitions and divergent estimates negatively affects societal perception, leading to scepticism and, ultimately, to a delay of eventual solutions. Societies must recognize the progress desertification ecology has made, leave behind concepts that no longer represent current knowledge, grasp the opportunity to better assess the extent and intensity of the problem, and, for the time being, realize that assessing desertification is an unsolved issue. 相似文献
16.
Fiddling on a different planet? 总被引：3，自引：0，他引：3
David J. Unwin 《Geoforum》2005,36(6):681-684
The recent commentaries in this journal by both [Hamnett, C., 2003. Contemporary human geography: fiddling while Rome burns, Geoforum 34, 1–3] and [Johnston, R., Hepple, L., Hoare, A., Jones, K., Plummer, P., 2003. Contemporary fiddling in human geography while Rome burns: has quantitative analysis been largely abandoned—and should it be? Geoforum 34, 157–161] do not recognise the phenomenal success of GIS in exporting a version of academic geography to the world at large. The note documents this success and explores possible implications for the discipline should it chose to engage with both the geographic information industry and the science that supports it. 相似文献
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In this paper, progressive methods for assessing drought severity from diverse points of view were conceived. To select a fundamental drought index, the performances of the Effective Drought Index (EDI) and 1-, 3-, 6-, 9-, 12-, and 24-month Standardized Precipitation Indices (SPIs) were compared for drought monitoring data accumulated over 200-year period from 1807 to 2006 for Seoul, Korea. The results confirmed that the EDI was more efficient than the SPIs in assessing both short and long-term droughts.We then proposed the following methods for modifying and supplementing the EDI: (1) CEDI, a corrected EDI that considers the rapid runoff of water resources after heavy rainfall; (2) AEDI, an accumulated EDI that considers the drought severity and duration of individual drought events; and (3) YAEDI, a year-accumulated negative EDI representing annual drought severity. In addition to these indices, to more accurately measure and diagnose droughts, we proposed the utilization of (4) the Available Water Resources Index (AWRI), an existing index that expresses the actual amount of available water.Using the improved methods above, we assessed and summarized important droughts that have occurred in Seoul over the 200 years from 1807 to 2006. 相似文献
18.
针对昆布素检测技术的难点,利用昆布素与苯胺蓝能特异性结合的特点,采用荧光分光光度计建立了昆布素含量的荧光快速检测方法。实验结果表明:NaOH浓度对昆布素立体结构影响较大,在昆布素解旋过程中加入70μL 3 mol/L的NaOH能使昆布素-苯胺蓝荧光复合物具有最大的荧光信号;通过三维荧光扫描,确定昆布素-苯胺蓝荧光复合物的最佳激发和发射波长分别为398 nm和502 nm,在此条件下昆布素-苯胺蓝荧光复合物浓度与其荧光值正相关(R2=0.999 4);方法学分析表明:该测定方法具有较高的精密度(RSD为2.52%)和稳定性(RSD为2.09%),检测范围为20~80 mg/L。基于所建立的昆布素含量快速检测方法,本文设计了有关提取温度、提取时间、pH以及乙醇浓度四个因素三个水平的正交试验对海带中昆布素的提取条件作了初步优化,结果表明:海带中昆布素的最佳提取条件是:置于稀盐酸(pH为1)溶液中于25℃下提取4 h,90%乙醇沉淀。 相似文献
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隐伏矿体三维成矿定量预测是以多元地学大数据为基础的矿产预测新技术与方法。本文基于隐伏矿体三维成矿定量预测的实际需要及相关方法步骤,采用集成二次开发的方式,设计实现了一套可在三维环境下基于大数据开展定量化成矿预测工作的软件系统。本文阐述了系统的总体架构及开发方式,并对系统中各个功能模块的设计及实现过程进行详细阐述。系统融合了当前三维成矿定量预测研究的最新方法及成果,内含数据库管理、三维地球物理正演、三维空间分析以及三维预测评价等功能模块,能够对多元地学大数据进行集成和分析预测。为了验证系统的适用性和有效性,该系统被应用于长江中下游成矿带钟姑矿田三维成矿定量预测研究,相关成果表明系统的建立不但能够深化和发展三维成矿预测理论,也为新时期基于大数据的隐伏矿体找矿勘探工作提供了新方法及有力工具。 相似文献
20.
Quantitative Calculation of Groundwater Vulnerability Assessment Based on Quantification Theory III 
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下载免费PDF全文 There are a lot of key qualitative variables in factors affecting groundwater vulnerability. The processing of qualitative variables of the existing superimposed index method generally relies on experience, so the results are normally subjective. Quantitative theory can handle qualitative variables quantitatively, achieve the unity of quantitative and qualitative indicators, highlight the decisive role of the main factors and reflect the actual situation more objectively. We took Yulin City as the research area to verify the feasibility and applicability of quantitative theory III, which is used for the quantitative evaluation of groundwater vulnerability. The results show that it has obvious advantage in the screening of indicators and the groundwater vulnerability partition, so it can be used as a quantitative calculation method of groundwater vulnerability assessment 相似文献