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Influence of root characteristics and soil variables on the uprooting mechanics of Avena sativa and Medicago sativa seedlings 
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下载免费PDF全文 Katharina Edmaier Benoît Crouzy Roland Ennos Paolo Burlando Paolo Perona 《地球表面变化过程与地形》2014,39(10):1354-1364
The success of seedlings and rejuvenated woody debris growing on river bedforms depends on the resistance to uprooting by flow provided by their simple root architecture. Avena sativa and Medicago sativa seedlings were used in flume experiments as prototypes for juvenile riparian plants. Very little is known about the magnitude of root anchoring forces and the role of secondary roots of such simple root systems. We performed 1550 vertical uprooting experiments on Avena sativa and Medicago sativa seedlings grown in quartz sand. Seedlings were pulled up by direct traction using a wheel driven by a computer‐controlled motor and the force was recorded. Roots were scanned and architectural parameters (root length and number of roots) determined. Uprooting force and work (the integral of the applied force times the distance over which it is applied) were then related to root architecture and soil variables. Resistance to uprooting increased with decreasing sediment size and sediment moisture content. The initial response of the root–soil system to uprooting showed linear elastic behaviour with modulus increasing with plant age. While the maximum uprooting force was found to increase linearly with total root length and be mainly dependent on the length of the main root, uprooting work followed a power law and has to be related to the whole root system. Thus, for the young plants we considered, secondary roots are responsible for the ability to withstand environmental disturbances in terms of duration rather than magnitude. This distinction between primary and secondary roots can be of crucial importance for seedlings of riparian species germinating on river bars and islands where inundation is a main cause of mortality. Beyond clarifying the biomechanical role of soil and root variables, the uprooting statistics obtained are useful in interpreting and designing ecomorphodynamic flume experiments. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
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Soil production and hillslope transport in mid‐latitudes during the last glacial–interglacial cycle: a combined data and modelling approach in northern Ardennes 下载免费PDF全文
下载免费PDF全文 The relative efficiency of various hillslope processes through Quaternary glacial–interglacial cycles in the mid‐latitudes is not yet well constrained. Based on a unique set of topographic and soil thickness data in the Ardennes (Belgium), we combine the new CLICHE model of climate‐dependent hillslope evolution with an inversion algorithm in order to get deeper insight into the ways and timing of hillslope dynamics under one such climatic cycle. We simulate the evolution of a synthetic hill reproducing the slope, curvature, and contributing area distributions of the hillslopes of a ~ 2500 km2 real area under a simple two‐stage 120‐kyr‐long climatic scenario with linear transitions between cold and warm stages. The inversion method samples a misfit function in the model parameter space, based on estimates of the fit of topographic derivative distributions in classes of soil thickness and of the relative frequencies of the predicted soil thickness classes. Though the inversion results show remarkable convergence patterns for most parameters, no unique solution emerges. We obtain five clusters of good fits, whose centroids are taken as acceptable model solutions. Based on the predicted time series of average denudation rate and soil thickness, plus snapshots of the soil distribution at characteristic times, we discuss these solutions and, comparing them with independent data not involved in the misfit function, we identify the most realistic scenario. Beyond providing first‐order estimates of several parameters that compare well with published data, our results show that denudation rates increase dramatically for a short time at both warm–cold and cold–warm transitions, when the mean annual temperature passes through the [0, ?5 °C] range. We also point to the overwhelming importance of solifluction in shaping hillslopes and transporting soil, and the role of depth‐dependent creep (including frost creep) throughout the climatic cycle, whereas the contributions of simple creep and overland flow are minor. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
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Ngwa Caroline N. Shu Bless N. Mbassa Benoît J. Aka Festus T. Wokwenmendam Pauline N. 《Mineralogy and Petrology》2020,114(1):57-70
Mineralogy and Petrology - We report olivine chemistry in basaltic rocks from the Mt. Cameroon Volcanic area, which is used as a proxy to understand mantle and early igneous processes along the... 相似文献
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Smail Slimani Nicolas Massei Johanna Mesquita Danièle Valdés Matthieu Fournier Benoît Laignel Jean-Paul Dupont 《Hydrogeology Journal》2009,17(8):1823-1832
The temporal variability of water-level fluctuations in the chalk aquifer of Upper Normandy, France is constrained by natural climate fluctuations and is closely linked to the regional geological patterns. The chalk plateaus are covered with 5–50 m thick semi-permeable surficial formations; the thickness of the underlying chalk aquifer varies from 50 to 300 m. The relationship among climate oscillations, piezometric levels, and geologic structure were investigated by correlation, Fourier spectral, and continuous wavelet analyses of selected piezometric time-series data. Analysis focused on two piezometers located on the uplifted side of a major fault and two piezometers on the downthrown side. After generalization to other piezometers in the region, it was deduced that, in the downthrown compartments, a substantial aquifer and surficial formations thickness would imply a strong attenuation of annual variability, while multi-year variability is clearly expressed. Conversely, in the uplifted compartments, a thin layer of surficial formations and small thickness of the chalk authorizes strong variations on the annual mode with respect to the contribution of long-term climatic oscillations (multi-year variability). The results then demonstrated—and proposed a spatial determination of—the differential influence of geological patterns on the filtering of climate-induced oscillations in piezometric variability. 相似文献
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The solar activity can be quantified by solar modulation parameter Φ that affects the heliospheric magnetic field. This activity influences the intensity of the galactic cosmic ray (GCR) particle flux within the solar system, and consequently, the differential primary particle spectra depend on the solar modulation parameter Φ (MeV). The modulation parameter Φ shows spatial and temporal variations (Leya and Masarik 2009). Some of the solar activity variations are cyclic and result in measurable effects as for example the 11‐year solar cycle. Variations in solar activity only induce small effects on the production of long‐lived cosmogenic radionuclides. This is due to the fact that activities measured in meteorites usually correspond to saturation values and represent long‐term average values. Long‐lived radionuclides often require millions of years of irradiation by GCR to reach saturation and therefore activity cycles average out. In contrast, one can expect strongly pronounced variations for saturation values caused by primary flux intensity variations, if short‐lived radionuclides with half‐lives ranging from days to a few years are investigated. Short‐lived cosmogenic nuclides were the subject of many experimental and theoretical investigations (e.g., Evans et al. 1982; Spergel et al. 1986; Neumann et al. 1997; Komura et al. 2002; Laubenstein et al. 2012). The aim of this work is to develop formulae for calculating production rates of radionuclides with short half‐life, taking into account temporal variations in the primary cosmic ray intensity. The developed formulae were applied to the Kosice and Chelyabinsk meteorites. The results for the Ko?ice meteorite were already published (Povinec et al. 2015). Here, we give a full explanation of underlying model. 相似文献
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Conditions for the arrest of a vertical propagating dyke 总被引：1，自引：0，他引：1
Magma ascent towards the Earth’s surface occurs through dyke propagation in the vast majority of cases. We investigate two
purely mechanical effects unrelated to cooling or solidification that lead to the arrest of propagation, so that no eruption
occurs. The first is that the input of magma from the source is not maintained continuously, such that a fixed volume of magma
is released. Laboratory experiments show that, in this case, the dyke stops at a finite distance from the source. This behaviour
is specific to the fracturing process in 3-D. We derive a relationship for the minimum magma volume required for an eruption
as a function of magma buoyancy and source depth. When large magma volumes are available, eruption may also be prevented by
a thick low density layer in the upper crust. Numerical studies of dyke propagation show that the dyke continues to rise even
though it is negatively buoyant. Magma accumulates in a swollen nose region at the interface between the low density layer
and the dense basement. Magma overpressure is largest at this interface and increases with increasing penetration into the
upper layer. It may become large enough to induce horizontal fractures in the dyke walls and lateral intrusion of a sill,
which prevents eruption. This requires that the thickness of the low density layer exceeds a threshold value that depends
on the density contrast between magma and host rock. If the magma volume is smaller than a threshold value, neither sill intrusion
nor eruption are possible and magma gets stored in a horizontal blade-shaped dyke straddling the interface. Scaling laws for
variations of ascent rate and for the minimum magma volume allow diagnosis of a failed eruption. 相似文献
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