A demonstration of the importance of bedload transport for fluvial bedrock erosion and knickpoint propagation

We provide field evidence for the role of bedload in driving fluvial incision and knickpoint propagation. Using aerial photographs, field surveys, and hydrological data, we constrain the incision history of a bedrock gorge 1200 m long and up to 20 m deep cut by Da'an River in western Taiwan. This reach of the river experienced 10 m of uplift during the 1999 Chi‐Chi earthquake. For five years following the earthquake, bedload was prevented from entering the uplift zone, the knickpoint was static and little incision took place. Bedload transport across the uplift zone resumed in 2004, initiating extremely rapid incision, with 620 m of knickpoint propagation and up to 20 m of downcutting by 2008. This change highlights the relative inefficiency of suspended sediment and the dominant role of bedload as a tool for fluvial erosion and knickpoint propagation. Once bedload tools became available, knickpoint propagation was influenced by geological structure, lithology, and drainage organization. In particular, a change in dip of the sandstone beds at the site caused a decrease of knickpoint propagation velocity. Copyright © 2012 John Wiley & Sons, Ltd.     

Mobility and potential bioavailability of traffic-derived trace metals in a ‘wet–dry’ tropical region,Northern Australia

The aqueous mobility and potential bioavailability of metals and metalloids in road runoff in a ‘wet–dry’ tropical location were assessed by analysing metal and metalloid concentrations in particulate, total dissolved and labile dissolved phases in runoff waters. Road-derived Al, Cu, Pb, Sb and Zn concentrations were substantially elevated in runoff when compared to receiving creek waters. Median dissolved concentrations in road runoff exceeded those in creek waters by up to an order of magnitude. Leaching experiments of road sediments confirmed that several metals and metalloids were released in high concentrations from road sediments. Labile Zn and Cu concentrations measured by diffusion gradients in thin films (DGT) showed that almost all dissolved Zn and up to half of dissolved Cu in runoff waters and in road sediment leachate were potentially bioavailable. Comparisons of dissolved metal concentrations in receiving waters affected by road runoff with ecosystem guideline levels, indicated a risk of reaching toxic levels of Cu and Zn in the receiving waters in the absence of adequate treatment or dilution. Low dilution rates of road runoff are likely to occur during late ‘dry’ season/early ‘wet’ season storms which have the potential to produce high metal concentrations derived from long periods of accumulation of road sediment at a time when creek flow rates are at their annual minimum.     

A method to reduce the temperature influence on measurements with thermoelectric pyranometers

Summary It is shown that the current of a pyranometer can be made independent of temperature by connecting a resistor of appropriate characteristics in series with the pyranometer. The temperature coefficient of the pyranometer with respect to the electromotive force should be made equal to the temperature coefficient of the resistance of the circuit. A resistor with a semilinear temperature characteristic and a negative temperature coefficient can be constructed by connecting a N.T.C. (Negative Temperature Coefficient) resistor in parallel with a resistor of constant resistance. A complete calculation is carried out for a case where the pyranometer is a Moll-Gorczynski solarimeter and the instrument indicating the current is a potentiometer. It turns out that the temperature influence on the radiation measurement can be almost eliminated.

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Zusammenfassung Es wird gezeigt, daß der Strom eines Pyranometers durch Einbau eines Resistors von geeigneter Charakteristik in Serie mit dem Pyranometer temperaturunabhängig gemacht werden kann. Zu diesem Zweck ist der Temperaturkoeffizient des Pyranometers in bezug auf die elektromotorische Kraft dem Temperaturkoeffizienten des Widerstandes des Stromkreises gleich zu machen. Ein Resistor mit einer semilinearen Temperaturcharakteristik und einem negativen Temperaturkoeffizienten kann durch Verbindung eines resistors mit negativen Temperaturkoeffizienten (N. T. C.) parallel zu einem Resistor von konstantem Widerstand konstruiert werden. Es wird eine vollständige Berechnung für den Fall der Kombination eines Solarimeters Moll-Gorczynski mit einem Potentiometer durchgeführt. Dabei ergibt sich, daß der Temperatureinfluß auf die Strahlungsmessung nahezu eliminiert werden kann.

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Résumé L'auteur démontre que le courant issu d'une pyranomètre peut être rendu indépendant des influences de la température en introduisant dans le circuit une thermistance appropriée placée en série. Le coefficient thermique du pyranomètre—compte tenu de la force électromotrice—doit être égal au coefficient thermique de la résistance du circuit. On peut construire une thermistance avec une caractéristique semi-linéaire de température et un coefficient thermique négatif en connectant en parallèle une résistance N. T. C. (Negative Temperature Coefficient) et une résistance constante. L'auteur présente un calcul complet pour le cas où le pyranomètre est un solarimètre Moll-Gorczynski et l'instrument de mesure un potentiomètre. Il en résulte que l'influence de la tempature sur la mesure du rayonnement peut presque être éliminée.

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With 4 Figures     

阿尔金山东段地质热年代学与构造演化

文中综合分析了青藏高原北缘阿尔金山东段地质热年代学和构造体系演化。阿尔金山东段从太古宙陆核发育而来,经历了元古宙稳定地台和新元古代大陆裂解阶段,形成了早古生代阿尔金洋和沟 弧 盆构造体系,发育了奥陶纪早期的板块俯冲、碰撞造山作用和奥陶纪-志留纪之交的岛弧岩浆活动(峰期年龄为443 Ma)。石炭纪洋盆闭合之后,该地区进入陆内构造发育阶段。其中,占主导地位的是以拉配泉断裂为代表的中生代伸展构造和新生代阿尔金断裂系的左行走滑断裂活动,它们分别控制了中生代两期热冷却事件和新生代地块快速抬升 冷却事件。地质热年代学年龄数据为阿尔金山东段不同时期形成的不同地块勾画了不同的热冷却历史,由此可区分不同时期不同构造事件对区域热冷却历史的影响。