High-frequency monitoring of hydrological and biogeochemical fluxes in forested catchments of southern Chile     

Cristián Frêne  Juan J. Armesto  Freddy Véliz  Fernando D. Alfaro  Kathleen C. Weathers 《水文研究》2021,35(5):e14175

The variability of rainfall-dependent streamflow at catchment scale modulates many ecosystem processes in wet temperate forests. Runoff in small mountain catchments is characterized by a quick response to rainfall pulses which affects biogeochemical fluxes to all downstream systems. In wet-temperate climates, water erosion is the most important natural factor driving downstream soil and nutrient losses from upland ecosystems. Most hydrochemical studies have focused on water flux measurements at hourly scales, along with weekly or monthly samples for water chemistry. Here, we assessed how water and element flows from broad-leaved, evergreen forested catchments in southwestern South America, are influenced by different successional stages, quantifying runoff, sediment transport and nutrient fluxes during hourly rainfall events of different intensities. Hydrograph comparisons among different successional stages indicated that forested catchments differed in their responses to high intensity rainfall, with greater runoff in areas covered by secondary forests (SF), compared to old-growth forest cover (OG) and dense scrub vegetation (CH). Further, throughfall water was greatly nutrient enriched for all forest types. Suspended sediment loads varied between successional stages. SF catchments exported 455 kg of sediments per ha, followed by OG with 91 kg/ha and CH with 14 kg/ha, corresponding to 11 rainfall events measured from December 2013 to April 2014. Total nitrogen (TN) and phosphorus (TP) concentrations in stream water also varied with rainfall intensity. In seven rainfall events sampled during the study period, CH catchments exported less nutrients (46 kg/ha TN and 7 kg/ha TP) than SF catchments (718 kg/ha TN and 107 kg/ha TP), while OG catchments exported intermediate sediment loads (201 kg/ha TN and 23 kg/ha TP). Further, we found significant effects of successional stage attributes (vegetation structure and soil physical properties) and catchment morphometry on runoff and sediment concentrations, and greater nutrients retention in OG and CH catchments. We conclude that in these southern hemisphere, broad-leaved evergreen temperate forests, hydrological processes are driven by multiple interacting phenomena, including climate, vegetation, soils, topography, and disturbance history.  相似文献   

Implementation of a coupled plastic damage distinct lattice spring model for dynamic crack propagation in geomaterials          下载免费PDF全文

Chao Jiang  Gao‐Feng Zhao 《国际地质力学数值与分析法杂志》2018,42(4):674-693

This paper studies dynamic crack propagation by employing the distinct lattice spring model (DLSM) and 3‐dimensional (3D) printing technique. A damage‐plasticity model was developed and implemented in a 2D DLSM. Applicability of the damage‐plasticity DLSM was verified against analytical elastic solutions and experimental results for crack propagation. As a physical analogy, dynamic fracturing tests were conducted on 3D printed specimens using the split Hopkinson pressure bar. The dynamic stress intensity factors were recorded, and crack paths were captured by a high‐speed camera. A parametric study was conducted to find the influences of the parameters on cracking behaviors, including initial and peak fracture toughness, crack speed, and crack patterns. Finally, selection of parameters for the damage‐plasticity model was determined through the comparison of numerical predictions and the experimentally observed cracking features.  相似文献   

Assessment of alternative adsorption models and global sensitivity analysis to characterize hexavalent chromium loss from soil to surface runoff          下载免费PDF全文

Chuan‐An Xia  Juxiu Tong  Bill X. Hu  Xiujie Wu  Alberto Guadagnini 《水文研究》2018,32(20):3140-3157

We investigate our ability to assess transfer of hexavalent chromium, Cr(VI), from the soil to surface runoff by considering the effect of coupling diverse adsorption models with a two‐layer solute transfer model. Our analyses are grounded on a set of two experiments associated with soils characterized by diverse particle size distributions. Our study is motivated by the observation that Cr(VI) is receiving much attention for the assessment of environmental risks due to its high solubility, mobility, and toxicological significance. Adsorption of Cr(VI) is considered to be at equilibrium in the mixing layer under our experimental conditions. Four adsorption models, that is, the Langmuir, Freundlich, Temkin, and linear models, constitute our set of alternative (competing) mathematical formulations. Experimental results reveal that the soil samples characterized by the finest grain sizes are associated with the highest release of Cr(VI) to runoff. We compare the relative abilities of the four models to interpret experimental results through maximum likelihood model calibration and four model identification criteria (i.e., the Akaike information criteria [AIC and AIC_C] and the Bayesian and Kashyap information criteria). Our study results enable us to rank the tested models on the basis of a set of posterior weights assigned to each of them. A classical variance‐based global sensitivity analysis is then performed to assess the relative importance of the uncertain parameters associated with each of the models considered, within subregions of the parameter space. In this context, the modelling strategy resulting from coupling the Langmuir isotherm with a two‐layer solute transfer model is then evaluated as the most skilful for the overall interpretation of both sets of experiments. Our results document that (a) the depth of the mixing layer is the most influential factor for all models tested, with the exception of the Freundlich isotherm, and (b) the total sensitivity of the adsorption parameters varies in time, with a trend to increase as time progresses for all of the models. These results suggest that adsorption has a significant effect on the uncertainty associated with the release of Cr(VI) from the soil to the surface runoff component.  相似文献   

A multi‐method approach to dating the burial and skeleton of Kiacatoo Man,New South Wales,Australia     

Timothy Pietsch  Justine Kemp  Colin Pardoe  Rainer Grün  Jon Olley  Rachel Wood 《第四纪科学杂志》2019,34(8):662-673

Kiacatoo Man, a large, rugged Aboriginal adult buried in the Lachlan riverine plains of southeastern Australia, was discovered in 2011. Laser‐ablation uranium series analysis on bone yielded a minimum age for the burial of 27.4 ± 0.4 ka (2σ). Single‐grain, optically stimulated luminescence ages on quartz sediment in which the grave had been dug gave a weighted mean age of 26.4 ± 1.5 ka (1σ). Luminescence samples from the grave infill and from sediment beneath the grave exhibit overdispersed dose distributions consistent with bioturbation or other disturbance, which has obscured the burial signal. The overlap between the minimum (U‐series) and maximum (luminescence) ages places the burial between 27.0 and 29.4 ka (2σ). Luminescence ages obtained from the channel belt of between 28 ± 2 and 25 ± 3 ka indicate that fluvial sedimentation was occurring before the Last Glacial Maximum, which is consistent with the broader geomorphic setting. Together, these results are internally and regionally consistent, and indicate that Kiacatoo Man was one of the more ancient individuals so far identified in Australia. His remains are important to our understanding of patterns of biological variation and other processes that have shaped people in the Murray‐Darling Basin through time. Copyright © 2019 John Wiley & Sons, Ltd.  相似文献   

Small hypervelocity particles captured in aerogel collectors: Location,extraction, handling and storage     

Andrew J. Westphal  Christopher Snead  Janet Borg  Eric Quirico  Pierre‐Ivan Raynal  Michael E. Zolensky  Gianluca Ferrini  Luigi Colangeli  Pasquale Palumbo 《Meteoritics & planetary science》2002,37(6):855-865

Abstract— It has now been about a decade since the first demonstrations that hypervelocity particles could be captured, partially intact, in aerogel collectors. But the initial promise of a bonanza of partially‐intact extraterrestrial particles, collected in space, has yet to materialize. One of the difficulties that investigators have encountered is that the location, extraction, handling and analysis of very small (10 μm and less) grains, which constitute the vast majority of the captured particles, is challenging and burdensome. Furthermore, current extraction techniques tend to be destructive over large areas of the collectors. Here we describe our efforts to alleviate some of these difficulties. We have learned how to rapidly and efficiently locate captured particles in aerogel collectors, using an automated microscopic scanning system originally developed for experimental nuclear astrophysics. We have learned how to precisely excavate small access tunnels and trenches using an automated micromanipulator and glass microneedles as tools. These excavations are only destructive to the collector in a very small area—this feature may be particularly important for excavations in the precious Stardust collectors. Using actuatable silicon microtweezers, we have learned how to extract and store “naked” particles—essentially free of aerogel—as small as 3 μm in size. We have also developed a technique for extracting particles, along with their terminal tracks, still embedded in small cubical aerogel blocks. We have developed a novel method for storing very small particles in etched nuclear tracks. We have applied these techniques to the extraction and storage of grains captured in aerogel collectors (Particle Impact Experiment, Orbital Debris Collector Experiment, Comet‐99) in low Earth orbit.  相似文献   

The monopole moment of the three-point correlation function of the two-degree Field Galaxy Redshift Survey     

Jun Pan  István Szapudi 《Monthly notices of the Royal Astronomical Society》2005,362(4):1363-1370

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Consolidation of double‐layered ground with vertical drains     

Xiao‐Wu Tang  Katsutada Onitsuka 《国际地质力学数值与分析法杂志》2001,25(14):1449-1465

Vertical drains are usually installed in subsoil consisting of several layers. Due to the complex nature of the problem, over the past decades, the consolidation properties of multi‐layered ground with vertical drains have been analysed mainly by numerical methods. An analytical solution for consolidation of double‐layered ground with vertical drains under quasi‐equal strain condition is presented in this paper. The main steps for the computation procedure are listed. The convergence of the series solution is discussed. The comparisons between the results obtained by the present analytical method and the existing numerical solutions are described by figures. The orthogonal relation for the system of double‐layered ground with vertical drains is proven. Finally, some consolidation properties of double‐layered ground with vertical drains are analysed. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

Non‐equilibrium concepts lead to a unified explanation of the formation of chondrules and chondrites     

Milton BLANDER  Arthur D. PELTON  In‐Ho JUNG  Richard WEBER 《Meteoritics & planetary science》2004,39(12):1897-1910

Abstract— Calculations of the formation of seven types of chondrules in Semarkona from a gas of solar composition were performed with the FACT computer program to predict the chemistries of oxides (including silicates), developed by the authors and their colleagues. The constrained equilibrium theory was used in the calculations with two nucleation constraints suggested by nucleation theory. The first constraint was the blocking of Fe and other metal gaseous atoms from condensing to form solids or liquids because of very high surface free energies and high surface tensions of the solid and liquid metals, respectively. The second constraint was the blocking of the condensation of solids and the formation of metastable liquid oxides (including silicates) well below their liquidus temperatures. Our laboratory experiments suggested subcooling of type IIA chondrule compositions of 400 degrees or more below the liquidus temperature. The blocking of iron leads to a supersaturation of Fe atoms, so that the partial pressure of Fe (p_Fe) is larger than the partial pressure at equilibrium (p_Fe(eq)). The supersaturation ratio S = p_Fe/p_Fe(eq) becomes larger than 1 and increases rapidly with a decrease in temperature. This drives the reaction Fe + H₂O ? H₂ + FeO to the right. With S = 100, the activity of FeO in the liquid droplet is 100 times as large as the value at equilibrium. The FeO activities are a function of temperature and provide relative average temperatures of the crystallization of chondrules. Our calculations for the LL3.0 chondrite Semarkona and our study of some non‐equilibrium effects lead to accurate representations of the compositions of chondrules of types IA, IAB, IB, IIA, IIAB, IIB, and CC. Our concepts readily explain both the variety of FeO concentrations in the different chondrule types and the entire process of chondrule formation. Our theory is unified and could possibly explain the formation of chondrules in all chondritic meteorites as well as provide a simple explanation for the complex chemistries of chondrites, and especially for type 3 chondrites.  相似文献   

Three dimensional simulation of fluid flow in X‐ray CT images of porous media     

A. Al‐Omari  E. Masad 《国际地质力学数值与分析法杂志》2004,28(13):1327-1360

A numerical scheme is developed in order to simulate fluid flow in three dimensional (3‐D) microstructures. The governing equations for steady incompressible flow are solved using the semi‐implicit method for pressure‐linked equations (SIMPLE) finite difference scheme within a non‐staggered grid system that represents the 3‐D microstructure. This system allows solving the governing equations using only one computational cell. The numerical scheme is verified through simulating fluid flow in idealized 3‐D microstructures with known closed form solutions for permeability. The numerical factors affecting the solution in terms of convergence and accuracy are also discussed. These factors include the resolution of the analysed microstructure and the truncation criterion. Fluid flow in 2‐D X‐ray computed tomography (CT) images of real porous media microstructure is also simulated using this numerical model. These real microstructures include field cores of asphalt mixes, laboratory linear kneading compactor (LKC) specimens, and laboratory Superpave gyratory compactor (SGC) specimens. The numerical results for the permeability of the real microstructures are compared with the results from closed form solutions. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

LU Vel (GJ 375): A M3.5Ve Flare and Double-Lined Spectroscopic Binary     

D. Montes  M. C. Gálvez  M. J. Fernández-Figueroa  I. Crespo-Chacón 《Astrophysics and Space Science》2006,304(1-4):367-369

High resolution echelle spectroscopic observations taken with the FEROS spectrograph at the 2.2 m telescope ESO confirm the binary nature of the flare M3.5V star LU Vel (GJ 375, RE J0958-462) previously reported by Christian and Mathioudakis (2002). Emission of similar intensity from both components is detected in the Balmer, Na i D₁&D₂, He i D₃, Ca ii H&K, and Ca ii IRT lines. We have determined precise radial velocities by cross correlation with radial velocity standard stars, which have allowed us to obtain for the first time the orbital solution of the system. The binary consists of two near-equal M3.5V components with an orbital period shorter than 2 days. We have analyzed the behaviour of the chromospheric activity indicators (variability and possible flares). In addition, we have determined its rotational velocity and kinematics.  相似文献