A simple model accounting for the uptake,transport, and deposition of wind‐eroded mineral particles in the hyperarid coastal Atacama Desert of northern Chile     

Stephane C. Alfaro  Valentina Flores‐Aqueveque  Gilles Foret  Sandrine Caquineau  Gabriel Vargas  Jose A. Rutllant 《地球表面变化过程与地形》2011,36(7):923-932

As previously observed in marine sediments collected downwind of African or South American continental sources, recent studies of sediment cores collected at the bottom of Mejillones Bay in north Chile (23°S) show a laminated structure in which the amount of particles of aeolian origin and their size create significant differences between the layers. This suggests inter‐annual to inter‐decadal variations in the strength of the local southerly winds responsible for (1) the erosion of the adjacent hyperarid surface of the Mejillones Pampa, and (2) the subsequent transport of the eroded particles towards the bay. A simple model accounting for the vertical uptake, transport, and deposition of the particles initially set into motion by wind at the surface of the pampa is proposed. This model, which could be adapted to other locations, assumes that the initial rate of (vertical) uptake is proportional to the (horizontal) saltation flux quantified by means of White's equation, that particles are lifted to a height (H), increasing with the magnitude of turbulence, and that sedimentation progressively removes the coarsest particles from the air column as it moves towards the bay. In this model, the proportionality constant (A) linking the vertical flux of particles with the horizontal flux, and the injection height (H) control the magnitude and size distribution of the deposition flux in the bay. Their values are determined using the wind speed measured over the pampa and the size distribution of particles collected in sediment traps deployed in the bay as constraints. After calibration, the model is used to assess the sensitivity of the deposition flux to the wind intensity variations. The possibility of performing such quantitative studies is necessary for interpreting precisely the variability of the aeolian material in the sediment cores collected at the bottom of Mejillones Bay. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Forest–savanna–morichal dynamics in relation to fire and human occupation in the southern Gran Sabana (SE Venezuela) during the last millennia     

Encarni Montoya  Valentí Rull  Nathan D. Stansell  Mark B. Abbott  Sandra Nogué  Broxton W. Bird  Wilmer A. Díaz 《Quaternary Research》2011,76(3):335-344

The southern Gran Sabana (SE Venezuela) holds a particular type of neotropical savanna characterized by the local occurrence of morichales (Mauritia palm swamps), in a climate apparently more suitable for rain forests. We present a paleoecological analysis of the last millennia of Lake Chonita (4°39′N–61°0′W, 884 m elevation), based on biological and physico-chemical proxies. Savannas dominated the region during the last millennia, but a significant vegetation replacement occurred in recent times. The site was covered by a treeless savanna with nearby rainforests from 3640 to 2180 cal yr BP. Water levels were higher than today until about 2800 cal yr BP. Forests retreated since about 2180 cal yr BP onwards, likely influenced by a higher fire incidence that facilitated a dramatic expansion of morichales. The simultaneous appearance of charcoal particles and Mauritia pollen around 2000 cal yr BP supports the potential pyrophilous nature of this palm and the importance of fire for its recent expansion. The whole picture suggests human settlements similar to today – in which fire is an essential element – since around 2000 yr ago. Therefore, present-day southern Gran Sabana landscapes seem to have been the result of the synergy between biogeographical, climatic and anthropogenic factors, mostly fire.  相似文献   

Seed germination of Southern Chihuahuan Desert plants in response to elevated temperatures     

R.M. Pérez-SánchezE. Jurado  L. Chapa-VargasJ. Flores 《Journal of Arid Environments》2011,75(10):978-980

High temperature is one of the main factors that prevent germination, through premature aging of the embryo. The high temperatures reached in the soil of arid environments can affect seed survival and plant establishment. In this study we tested whether seed exposure to high temperature (40 °C and 70 °C) affected germination of eight species common to the Southern Chihuahuan Desert, and used for fodder, firewood and timber, fiber, edible flowers, fruits and stems. The responses to heat varied between species. Two of the tested species were not affected by heat exposure; for two other species germination was higher, and for the remaining four, germination was lower. There was also a delay of germination after heat exposure. Seeds of three species germinated >1 d slower after exposure to high temperatures. These results could help establish management programs for these Chihuahuan desert species under a climate change scenario.  相似文献   

Study of Metal Distribution in Raw and Screened Swine Manure   总被引：1，自引：0，他引：1  

Ricardo Luís Radis Steinmetz  Airton Kunz  Valderi Luiz Dressler  Érico Marlon de Moraes Flores  Ayrton Figueiredo Martins 《洁净——土壤、空气、水》2009,37(3):239-244

The growth of industrial swine production over the last few years has led to a growth in concern over effluents generated by the activity. Several elements, mainly toxic metals, can be present in swine wastewater and can have a serious environmental impact. It is important, therefore, to know the metal concentration before the discharge of wastewater. In this work the temporal metal distribution in swine manure and its potential reduction using coarse (2 mm) and fine (<0.45 μm) liquid‐solid separation techniques were investigated. In order to do this, different swine manure sample preparation methods for Al, Ba, Cd, Co, Cr, Cu, Fe, Mg, Mn, Ni, Pb, Sr and Zn determination by Inductively Coupled Plasma Optical Emission Spectrometry (ICP OES) were tested. The acid mixtures used to digest the manure sample significantly affected the metal recovery. Good analyte recoveries were observed with nitric acid/hydrogen peroxide mixtures or nitric acid/perchloric acid mixtures. Sulfuric acid/hydrogen peroxide mixtures produced inconsistent results and poor recoveries, mainly for Ba and Pb. It was observed that metal concentrations in swine manure varied greatly with time, up to one order of magnitude, due to changes in swine production such as feed and animal numbers. Metals concentrations observed in the raw wastewater exceeded Brazilian limits for discharge into water bodies and recommendations for agricultural use. Results obtained from the liquid‐solid separation study showed that metals in the raw swine manure were not removed with coarse screening. However, the major fraction of metals were removed by filtration (0.45 μm), with the exception of Na, K and Sr. Thus, the use of liquid‐solid separation techniques that capture the fine solid fractions (and associated metals) from raw manure can have a favorable impact on the environment and contribute to swine production wastewater treatment.  相似文献   

TPH and PAH concentrations in the subsoil of polyduct segments, oil pipeline pumping stations, and right-of-way pipelines from Central Mexico     

Rosario Iturbe  Alejandrina Castro  Guillermina Perez  Carlos Flores  Luis G. Torres 《Environmental Geology》2008,55(8):1785-1795

For the year 1996, 366 incidents related with clandestine poaching of oil-products were reported in Mexico, 159 in 1997, and 240 in 1998. For the year 2003 (the most recently reported figure), there were 136 events. Petroleos Mexicanos (PEMEX), very concerned with the environmental agenda, has developed programs oriented to diminish contamination levels in all of its oil facilities. This work was aimed at characterizing zones around polyduct segments, pipelines, pumping stations, and right-of-way pipelines located in the center of Mexico. The TPH contaminated sites were, in decreasing order, polyduct km 39 + 150 > polyduct km 25 + 020 > Zoquital > Tepetitlan > Catalina > Venta Prieta > Ceiba. Most of the sampled points showed the presence of more than one of the 16 PAHs considered by USEPA as priority pollutants. Except point TEPE 2A, where no PAHs were detected, all the sampled points showed values from low to medium concentrations; however, values found at the sites did not exceed the limits according to the Mexican or the American legislation. The place with the largest contaminated area corresponded to the polyduct km 39 + 150, with 130 m² and 260 m³ to be treated. The least contaminated area was that around the JUAN 4 point at Juandho station, with 20 m² and 22 m³ of contaminated soil. The total area to be treated is about 230 m² and 497 m³.  相似文献   

Comparison of streamflow recession between plantations and native forests in small catchments in Central-Southern Chile     

Francisco Balocchi  Neftali Flores  José Luis Arumí  Andrés Iroumé  Don A. White  Richard P. Silberstein  Pablo Ramírez de Arellano 《水文研究》2021,35(6):e14182

In central Chile, many communities rely on water obtained from small catchments in the coastal mountains. Water security for these communities is most vulnerable during the summer dry season and, from 2010 to 2017, rainfall during the dry season was between 20% and 40% below the long-term average. The rate of decrease in stream flow after a rainfall event is a good measure of the risk of flow decreasing below a critical threshold. This risk of low flow can be quantified using a recession coefficient (α) that is the slope of an exponential decay function relating flow to time since rainfall. A mathematical model was used to estimate the recession coefficient (α) for 142 rainstorm events (64 in summer; 78 in winter) in eight monitored catchments between 2008 and 2017. These catchments all have a similar geology and extend from 35 to 39 degrees of latitude south in the coastal range of south-central Chile. A hierarchical cluster analysis was used to test for differences between the mean value of α for different regions and forest types in winter and summer. The value of α did not differ (p < 0.05) between catchments in winter. Some differences were observed during summer and these were attributed to morphological differences between catchments and, in the northernmost catchments, the effect of land cover (native forest and plantation). Moreover, α for catchments with native forest was similar to those with pine plantations, although there was no difference (p < 0.05) between these and Eucalyptus plantations. The recession constant is a well-established method for understanding the effect of climate and disturbance on low flows and baseflows and can enhance local and regional analyses of hydrological processes. Understanding the recession of flow after rainfall in small headwater catchments, especially during summer, is vital for water resources management in areas where the establishment of plantations has occurred in a drying climate.  相似文献   

Physical Conditions in Regions of Line Formation of Solar Type Stars     

L. H. Rodrigues-Merino  O. Cardona  A. Flores 《Astrophysics》2015,58(3):406-419

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Geology and paleomagnetism of El Potrero pluton, Baja California: Understanding criteria for timing of deformation and evidence of pluton tilt during batholith growth     

Gabriel Chvez Cabello  Roberto Molina Garza  Luis Delgado Argote  Rubn Contreras Flores  Elisa Ramírez  Amabel Ortega Rivera  Harald Bhnel  James Lee 《Tectonophysics》2006,424(1-2):1-17

The 102 Ma El Potrero pluton, in the western foothills of Sierra San Pedro Mártir, in north-central Baja California, was emplaced during a long period of contractional deformation bracketed between 132 and 85 Ma that affected this segment of the Peninsular Ranges Batholith. The pluton records regional and emplacement related deformation manifested by: (1) a solid-state fabric developed on its eastern contact, which is produced by eastward lateral pluton expansion; (2) cleavage triple point zones in the host-rock NW and SE of the pluton; (3) subhorizontal ductile shear zones indicative of top-to-the-east transport; (4) magmatic and tectonic foliations parallel to regional structural trends and regional shear zones; (5) variable axial ratios of microgranitoid enclaves close to pluton–wall rock contacts; (6) evidence of brittle-emplacement mechanisms in the western border of the pluton, which contrast with features indicating mainly ductile mechanisms toward the east; and, (7) markedly discordant paleomagnetic directions that suggest emplacement in an active tectonic setting. The overall mean for 9 accepted paleomagnetic sites is Dec = 34.6°, I = 25.7° (k = 88.3, α₉₅ = 5.5°), and is deviated  35° with respect to the reference cratonic direction. This magnetization is interpreted to indicate a combination of tilt due to initial drag during vertical diapiric ascent (or westward lateral-oblique expansion) of the adjacent San Pedro Mártir pluton and later rotation ( 15°) by Rosarito Fault activity in the southwest; this rotation may have occurred as eastward contraction acted to fill the space emptied by the ascending San Pedro Mártir pluton. The Rosarito fault may have tilted several plutons in the area (Sierra San Pedro Mártir, El Potrero, San José, and Encinosa). Magnetic susceptibility fabrics for 13 sites reflect mostly emplacement-related stress and regional stress. Paleomagnetic data and structural observations lead us to interpret the El Potrero pluton as a syntectonic pluton, emplaced within a regional shear zone delimited by the Main Mártir Thrust and the younger Rosarito Fault.  相似文献   

Geologic and geomorphic controls of coal development in some Tertiary Rocky Mountain basins, USA     

Romeo M. Flores 《International Journal of Coal Geology》1993,23(1-4)

Previous investigations have not well defined the controls on the development of minable coals in fluvial environments. This study was undertaken to provide a clearer understanding of these controls, particularly in of the lower Tertiary coal-bearing deposits of the Raton and Powder River basins in the Rocky Mountain region of the United States. In this region, large amounts of coals accumulated in swamps formed in the flow-through fluvial systems that infilled these intermontane basins. Extrabasinal and intrabasinal tectonism partly controlled the stratigraphic and facies distributions of minable coal deposits. The regional accumulation of coals was favored by the rapid basin subsidence coupled with minimal uplift of the source area. During these events, coals developed in swamps associated with anastomosed and meandering fluvial systems and alluvial fans. The extensive and high rate of sediment input from these fluvial systems promoted the formation of ombrotrophic, raised swamps, which produced low ash and anomalously thick coals. The petrology and palynology of these coals, and the paleobotany of the associated sediments, suggest that ombrotrophic, raised swamps were common in the Powder River Basin, where the climate during the early Tertiary was paratropical. The paleoecology of these swamps is identical to that of the modern ombrotrophic, raised swamps of the Baram and Mahakam Rivers of Borneo.  相似文献   

Spatial pattern of photospheric granules in a sunspot neighborhood     

Ernesto R. Rodríguez Flores  Rafael Gmez Díaz  Ramn E. Rodríguez Taboada 《Journal of Atmospheric and Solar》2005,67(17-18):1728

Based on high-resolution (0.3 arcsec) observations, we studied the behavior of solar granulation in the neighborhood of a sunspot. The bright granules’ spatial distribution and the granules’ surface density as a function of distance from the center of the sunspot umbra were determined.Bright granules distribute delimiting cells of dimensions in the mesogranular scale. The mean diameter of these cells does not show significant variation with the variation of the magnetic field of the sunspot. The granules’ surface density does not show significant variation with distance to the sunspot umbra. Both results point to a very weak, if any, influence of the sunspot magnetic field at distances greater than 20 arcsec.  相似文献