Differences in preferential flow with antecedent moisture conditions and soil texture: Implications for subsurface P transport

Preferential flowpaths transport phosphorus (P) to agricultural tile drains. However, if and to what extent this may vary with soil texture, moisture conditions, and P placement is poorly understood. This study investigated (a) interactions between soil texture, antecedent moisture conditions, and the relative contributions of matrix and preferential flow and (b) associated P distributions through the soil profile when fertilizers were applied to the surface or subsurface. Brilliant blue dye was used to stain subsurface flowpaths in clay and silt loam plots during simulated rainfall events under wet and dry conditions. Fertilizer P was applied to the surface or via subsurface placement to plots of different soil texture and moisture condition. Photographs of dye stains were analysed to classify the flow patterns as matrix dominated or macropore dominated, and soils within plots were analysed for their water‐extractable P (WEP) content. Preferential flow occurred under all soil texture and moisture conditions. Dye penetrated deeper into clay soils via macropores and had lower interaction with the soil matrix, compared with silt loam soil. Moisture conditions influenced preferential flowpaths in clay, with dry clay having deeper infiltration (92 ± 7.6 cm) and less dye–matrix interaction than wet clay (77 ± 4.7 cm). Depth of staining did not differ between wet (56 ± 7.2 cm) and dry (50 ± 6.6 cm) silt loam, nor did dominant flowpaths. WEP distribution in the top 10 cm of the soil profile differed with fertilizer placement, but no differences in soil WEP were observed at depth. These results demonstrate that large rainfall events following drought conditions in clay soil may be prone to rapid P transport to tile drains due to increased preferential flow, whereas flow in silt loams is less affected by antecedent moisture. Subsurface placement of fertilizer may minimize the risk of subsurface P transport, particularily in clay.     

南极无冰区古海蚀龛石英颗粒表面结构特征及其环境意义

石英砂表面结构特征组合能指示沉积物的搬运历史和沉积环境。利用电镜扫描方法分析了南极法尔兹半岛上海蚀成因的古海蚀龛沉积物中的石英砂表面结构特征组合。结果表明，在所有的石英砂表面上均表现出冰川和水流共同作用的结构特征组合，龛中沉积物是冰水沉积环境下的产物，在沉积过程中，沉积物先经过较薄的冰川搬运，后经历了不同能量的流水改造作用，但冰川和流水的搬运距离有限。上述研究结果表明，南极法尔兹半岛上的冰盖解体并退出长城站区的时间应早于4600aBP。     

Controls of mineral reactions in high-grade garnet–wollastonite–scapolite-bearing calcsilicate rocks: an example from Anakapalle, Eastern Ghats, India

ABSTRACT A suite of garnet-wollastonite-scapolite-bearing calcsilicate granulites from the Eastern Ghats has been investigated to document the controls of mineral reactions during the metamorphic evolution of the deep continental crust. The rocks studied show heterogeneity in modal mineralogy and phase compositions in millimetre-sized domains. Textural relations, and the compositional plots of the phases, established that the clinopyroxene exerts a strong influence on the formation and composition of garnet in the complex natural system. P-T estimates using the vapour-independent equilibria involving garnet define a near isobaric cooling path from c. 850C at c. 5.5–5.2 kbar. The deduced trajectory tallies well with the terminal segment of the overall retrograde P-T path construed from the associated rocks using well-calibrated thermobarometers. The ubiquitous occurrence of wollastonite and scapolite in the main calcsilicate body suggests low a_CO2 during peak metamorphic condition. Fluid compositions constrained from mineral-fluid equilibria of the garnet-bearing assemblages show domainal variations as a function of the compositions of the solid phases, e.g. garnet and clinopyroxene. A quantitative log/_CO2-log/_O2 diagram has been constructed to depict the stability of the different calcsilicate assemblages as functions of the compositions and the behaviour of these fugitive species. The results of the mineral-fluid equilibria and the quantitative fluid/rock ratio calculations, in conjunction with the topological constraints, imply vapour-deficient meta-morphism in the rocks studied. It is argued that f_O2 during peak metamorphism was monitored by the ambient f_O2. Subsequently, during retrogression, different domains evolved independently, whereas the fluid composition was controlled by the mineral-fluid equilibria.     

人工神经网络信息融合及其在机场识别中的应用研究

以机场识别为研究对象,以两种改进的BP网络作为算法工具,以TM影像作为原始数据,在特征级信息融合技术框架下进行机场识别研究。首先对可用于机场识别的特征进行分析,提出使用光谱特征、纹理特征和几何形状特征这三个特征的7维矢量作为BP网络的输入,并对BP网络的训练、测试和识别三个过程进行了详细的讨论。     

一种用于版权保护的混合域数字图像水印算法

提出一种用于版权保护的混合域数字图像水印算法。该算法具有以下特点:①根据宿主图像自身局部特性,实现基于图像内容的自适应块分割;②充分利用人眼视觉感知特性,实现嵌入位置的自适应确定及水印信息的自适应嵌入;③数字水印的提取不需要原始载体图像。实验结果表明该混合域自适应图像水印算法不仅具有较好的透明性,而且对诸如叠加噪声、JPEG压缩、平滑滤波、几何剪切、图像增强、马赛克效果等攻击均具有较好的鲁棒性。     

三维城市模型中建筑小品的建模方法

提出了一种基于CAD工具的小品建模工艺流程,着重介绍了建模的思路、技术方法和需要注意的关键问题。     

遥感影像分类的一种二叉决策树自动生成方法

提出了一种决策树自动生成的方法,介绍了其阈值确定方法、数据结构、决策树生成流程,给出了一个自动生成的实例,并与人工生成的决策树进行了比较。     

基于改进 GLCM 的侧扫声纳影像分类研究

提出一种基于改进GLCM的算法IGLCM用于侧扫声纳影像的分类,IGLCM反映像素与其邻域像素的灰阶联合分布,全面描述像素与其邻域像素所在区域的纹理特征。利用GLCM和IGLCM分别提取4种纹理特征,应用支持向量机对侧扫声纳海底底质进行分类。研究结果表明,IGLCM分类精度优于GLCM,更适合侧扫声纳分类。     

结合纹理信息和支持向量机的金钟藤信息提取

为了寻找快速准确、方便调查病态性入侵植物金钟藤分布的方法和技术,该文以海南省定安县为研究区,结合光谱信息与纹理信息,运用支持向量机的分类方法,提取该地区金钟藤信息,并将分类的结果与最大似然法、单源数据(B3波段图像)的支持向量机分类结果进行定性与定量的比较分析。结果表明:基于比值植被指数、B3波段为纹理信息源的支持向量机方法有利于金钟藤信息的提取;通过结合纹理信息和支持向量机的方法,实现了分类精度的提高。     

Benefits of design modifications to the Birkbeck bedload sampler illustrated by flash‐floods in an ephemeral gravel‐bed channel

The benefits of three simple modifications to the design of a Birkbeck bedload slot‐sampling system that has been continuously operating in Nahal Eshtemoa, Israel, since the early 1990s are demonstrated. The modifications include the deployment of a removable slot cover which delays the accumulation of sediment, so allowing sampling at late stages of a flood and, in conjunction with other samplers, extending the period of sampling during a flood wave; inclusion of a slot the size of which is adjustable so that that the probability of sampling the largest clast sizes in transit as bedload can be increased post‐installation, once knowledge is gained about the bedload grain‐size distribution; and a sampler side‐wall door that allows stratification and textural changes within the accumulated bedload to be identified, so promoting intelligent sampling of the deposit for grain‐size determination. Results from seven flash‐floods are presented and discussed, with recommendations for bedload monitoring, particularly in rivers where sediment flux is high and dynamic sediment records are inevitably short because of instrumental limitations. Copyright © 2006 John Wiley & Sons, Ltd.